fix(auth): harden OIDC flow, token validation, session, and bearer handling

- replay entry covers exp + clock-skew window; callback GET-only (RFC 6749)
- callback rate-limit returns 429 + Retry-After; panic-recovery sets no-store
- cross-chunk integrity for chunked tokens; bounded chunked-token read scan
- HTTPError classification so 5xx/429 token-endpoint responses retry
- redaction of token/code/state in logs; per-source external auth gate

auth_flow.go

@@ -1,6 +1,7 @@
 package traefikoidc
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"strings"
@@ -14,6 +15,16 @@ func (t *TraefikOidc) validateRedirectCount(session *SessionData, rw http.Respon
 	if redirectCount >= maxRedirects {
 		t.logger.Errorf("Maximum redirect limit (%d) exceeded, possible redirect loop detected", maxRedirects)
 		session.ResetRedirectCount()
+		// Persist the reset so the NEXT request starts at 0 and can
+		// attempt auth again. Without Save, the reset only touched the
+		// in-memory session value (dirty flag set but never flushed): the
+		// cookie still carried the old count, so every subsequent
+		// request re-observed redirect_count==max and the user was
+		// hard-locked on 508 for the whole session with no recovery
+		// (R123).
+		if err := session.Save(req, rw); err != nil {
+			t.logger.Errorf("Failed to save session after redirect reset: %v", err)
+		}
 		t.sendErrorResponse(rw, req, "Authentication failed: Too many redirects", http.StatusLoopDetected)
 		return fmt.Errorf("redirect limit exceeded")
 	}
@@ -68,9 +79,34 @@ func (t *TraefikOidc) prepareSessionForAuthentication(session *SessionData, csrf
 //   - req: The HTTP request initiating authentication.
 //   - session: The session data to prepare for authentication.
 //   - redirectURL: The pre-calculated callback URL (redirect_uri) for this middleware instance.
+//
+// rateLimitPerSourceAuth applies the (optional) per-external-source auth
+// throttle at an OIDC gate. Returns true if the request was already
+// answered with 429 and the caller must return. No-op when the limiter is
+// disabled (PerSourceLoginRateLimit <= 0) or the source is internal.
+func (t *TraefikOidc) rateLimitPerSourceAuth(rw http.ResponseWriter, req *http.Request) bool {
+	if t.perSourceLimiter == nil {
+		return false
+	}
+	if t.perSourceLimiter.allow(req) {
+		return false
+	}
+	rw.Header().Set("Retry-After", "1")
+	t.sendErrorResponse(rw, req, "Too many authentication attempts, please try again shortly", http.StatusTooManyRequests)
+	return true
+}
+
 func (t *TraefikOidc) defaultInitiateAuthentication(rw http.ResponseWriter, req *http.Request, session *SessionData, redirectURL string) {
 	t.logger.Debugf("Initiating new OIDC authentication flow for request: %s", req.URL.RequestURI())
 
+	// Per-external-source throttle on login initiation: a single host
+	// flooding the route with auth starts shouldn't be able to spin up an
+	// unbounded number of IdP round-trips or wear the shared token-origin
+	// bucket down for everyone (R185).
+	if t.rateLimitPerSourceAuth(rw, req) {
+		return
+	}
+
 	// Check and handle redirect limits
 	if err := t.validateRedirectCount(session, rw, req); err != nil {
 		return
@@ -97,9 +133,42 @@ func (t *TraefikOidc) defaultInitiateAuthentication(rw http.ResponseWriter, req
 		return
 	}
 
+	// Build the provider authorize URL BEFORE mutating the session. A URL-
+	// build failure must not clear a valid existing session, and must not
+	// emit an empty-Location redirect (browsers reload the current page,
+	// re-entering this flow and bumping the redirect count until the hard
+	// 508). Fail closed with an explicit status instead (R142).
+	authURL := t.buildAuthURL(redirectURL, csrfToken, nonce, codeChallenge)
+	if authURL == "" {
+		t.logger.Errorf("Failed to build provider authorize URL; aborting login flow")
+		http.Error(rw, "Failed to build provider authorize URL", http.StatusInternalServerError)
+		return
+	}
+
+	// When dynamic client registration is enabled but has not yet produced a
+	// client_id (registration pending or failed), forging an authorize URL
+	// with client_id="" would send the user to the provider on a broken
+	// flow. Fail with a clear status instead of redirecting. This guard
+	// must run BEFORE prepareSessionForAuthentication re-seeds the session:
+	// re-seeding (and the save that follows) would otherwise mutate and
+	// persist the session even though we are about to answer 503 with no
+	// redirect — discarding any existing session state for no reason (R163).
+	// Snapshot clientID under metadataMu: DCR rewrites it at runtime (R137).
+	clientID, _, _, _, _ := t.clientCredentials()
+	if t.dcrConfig != nil && t.dcrConfig.Enabled && clientID == "" {
+		t.logger.Errorf("OIDC dynamic client registration has not produced a client_id; refusing to redirect to provider")
+		http.Error(rw, "Identity provider registration pending", http.StatusServiceUnavailable)
+		return
+	}
+
 	// Clear existing session data and set new authentication state
 	t.prepareSessionForAuthentication(session, csrfToken, nonce, codeVerifier, req.URL.RequestURI())
 
+	// Persist the redirect_uri so the callback reuses the exact value sent
+	// to the IdP, instead of rebuilding it from the (client-affectable)
+	// callback request's X-Forwarded-Host (R136).
+	session.SetRedirectURL(redirectURL)
+
 	session.MarkDirty()
 
 	if err := session.Save(req, rw); err != nil {
@@ -111,20 +180,13 @@ func (t *TraefikOidc) defaultInitiateAuthentication(rw http.ResponseWriter, req
 	t.logger.Debugf("Session saved before redirect. CSRF: %s, Nonce: %s",
 		csrfToken, nonce)
 
-	authURL := t.buildAuthURL(redirectURL, csrfToken, nonce, codeChallenge)
-
-	// When dynamic client registration is enabled but has not yet produced a
-	// client_id (registration pending or failed), forging an authorize URL
-	// with client_id="" would send the user to the provider on a broken
-	// flow. Fail with a clear status instead of redirecting.
-	if t.dcrConfig != nil && t.dcrConfig.Enabled && t.clientID == "" {
-		t.logger.Errorf("OIDC dynamic client registration has not produced a client_id; refusing to redirect to provider")
-		http.Error(rw, "Identity provider registration pending", http.StatusServiceUnavailable)
-		return
-	}
-
 	t.logger.Debugf("Redirecting user to OIDC provider: %s", authURL)
 
+	// 302s into the IdP must not be heuristically cacheable (RFC 7234):
+	// a stale, cached redirect could replay the pre-re-authentication URL.
+	// Every other auth response sets no-store; these redirects were missed
+	// (R147).
+	rw.Header().Set("Cache-Control", "no-store")
 	http.Redirect(rw, req, authURL, http.StatusFound)
 }
 
@@ -135,7 +197,31 @@ func (t *TraefikOidc) defaultInitiateAuthentication(rw http.ResponseWriter, req
 //   - rw: The HTTP response writer.
 //   - req: The callback request containing authorization code and state.
 //   - redirectURL: The fully qualified callback URL (used in the token exchange request).
+//
+// clearOneTimeAuthState clears the one-time CSRF/nonce/PKCE-verifier after a
+// callback that consumed the authorization code but then failed, and persists
+// the cleared state. Without it the failed session stays in a pending-auth
+// state and a retried callback would re-exchange a fresh code before failing
+// again. Mirrors the cleanup on the exchange-failure / empty-access-token
+// paths (R134).
+func (t *TraefikOidc) clearOneTimeAuthState(session *SessionData, req *http.Request, rw http.ResponseWriter) {
+	session.SetCSRF("")
+	session.SetNonce("")
+	session.SetCodeVerifier("")
+	if saveErr := session.Save(req, rw); saveErr != nil {
+		t.logger.Errorf("Failed to save session after callback failure: %v", saveErr)
+	}
+}
+
 func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request, redirectURL string) {
+	// Per-external-source throttle on the authorization-code callback: this
+	// is where the one-time code exchange (server round-trip + token
+	// cache write) happens, so a single source can't brute-force
+	// repeated code exchanges or drown the shared limiter (R185).
+	if t.rateLimitPerSourceAuth(rw, req) {
+		return
+	}
+
 	session, err := t.sessionManager.GetSession(req)
 	if err != nil {
 		t.logger.Errorf("Session error during callback: %v", err)
@@ -144,15 +230,28 @@ func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request,
 	}
 	defer session.returnToPoolSafely()
 
-	t.logger.Debugf("Handling callback, URL: %s", req.URL.String())
+	t.logger.Debugf("Handling callback, URL: %s", redactCallbackURL(req.URL.String()))
 
 	if req.URL.Query().Get("error") != "" {
 		errorDescription := req.URL.Query().Get("error_description")
 		if errorDescription == "" {
 			errorDescription = req.URL.Query().Get("error")
 		}
-		t.logger.Errorf("Authentication error from provider during callback: %s - %s", req.URL.Query().Get("error"), errorDescription)
-		t.sendErrorResponse(rw, req, fmt.Sprintf("Authentication error from provider: %s", errorDescription), http.StatusBadRequest)
+		// error / error_description are attacker-controlled query params.
+		// Sanitize before logging and before echoing back to the client:
+		// an embedded newline would inject a forged line into (especially
+		// structured) logs, and unbounded length would bloat the log and
+		// the error response (R145).
+		sanitizeErr := func(s string) string {
+			s = strings.NewReplacer("\n", " ", "\r", " ").Replace(s)
+			const maxErrLen = 512
+			if len(s) > maxErrLen {
+				s = s[:maxErrLen]
+			}
+			return s
+		}
+		t.logger.Errorf("Authentication error from provider during callback: %s - %s", sanitizeErr(req.URL.Query().Get("error")), sanitizeErr(errorDescription))
+		t.sendErrorResponse(rw, req, fmt.Sprintf("Authentication error from provider: %s", sanitizeErr(errorDescription)), http.StatusBadRequest)
 		return
 	}
 
@@ -166,7 +265,7 @@ func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request,
 	csrfToken := session.GetCSRF()
 	if csrfToken == "" {
 		t.logger.Errorf("CSRF token missing in session during callback. Authenticated: %v, Request URL: %s",
-			session.GetAuthenticated(), req.URL.String())
+			session.GetAuthenticated(), redactCallbackURL(req.URL.String()))
 
 		cookie, err := req.Cookie("_oidc_raczylo_m")
 		if err != nil {
@@ -199,6 +298,13 @@ func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request,
 		return
 	}
 
+	// Use the redirect_uri persisted at initiate time (must match what was
+	// sent to the IdP's authorize endpoint). Fall back to the rebuilt one
+	// only for pre-existing sessions that predate R136 (R136).
+	if stored := session.GetRedirectURL(); stored != "" {
+		redirectURL = stored
+	}
+
 	tokenResponse, err := t.tokenExchanger.ExchangeCodeForToken(req.Context(), "authorization_code", code, redirectURL, codeVerifier)
 	if err != nil {
 		t.logger.Errorf("Failed to exchange code for token during callback: %v", err)
@@ -207,30 +313,29 @@ func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request,
 		// may still be unconsumed at the provider, so a replayed callback
 		// must re-authenticate rather than revalidate a stale
 		// state/nonce/code_verifier. Mirrors the cleanup on success.
-		session.SetCSRF("")
-		session.SetNonce("")
-		session.SetCodeVerifier("")
-		if saveErr := session.Save(req, rw); saveErr != nil {
-			t.logger.Errorf("Failed to save session after callback exchange failure: %v", saveErr)
-		}
+		t.clearOneTimeAuthState(session, req, rw)
 		t.sendErrorResponse(rw, req, "Authentication failed: Could not exchange code for token", http.StatusInternalServerError)
 		return
 	}
 
 	if tokenResponse.AccessToken == "" {
 		t.logger.Errorf("Token endpoint returned no access token during callback")
-		session.SetCSRF("")
-		session.SetNonce("")
-		session.SetCodeVerifier("")
-		if saveErr := session.Save(req, rw); saveErr != nil {
-			t.logger.Errorf("Failed to save session after empty access token: %v", saveErr)
-		}
+		t.clearOneTimeAuthState(session, req, rw)
 		t.sendErrorResponse(rw, req, "Authentication failed: Token endpoint returned no access token", http.StatusInternalServerError)
 		return
 	}
 
 	if err = t.verifyToken(tokenResponse.IDToken); err != nil {
 		t.logger.Errorf("Failed to verify id_token during callback: %v", err)
+		t.clearOneTimeAuthState(session, req, rw)
+		if errors.Is(err, ErrRateLimitExceeded) {
+			// Rate-limit exhaustion must be a 429 + Retry-After, not a
+			// generic 500: a single source's burst currently degrades
+			// every user's callback to "server error" (R179).
+			rw.Header().Set("Retry-After", "1")
+			t.sendErrorResponse(rw, req, "Authentication failed: Too many requests, please retry", http.StatusTooManyRequests)
+			return
+		}
 		t.sendErrorResponse(rw, req, "Authentication failed: Could not verify ID token", http.StatusInternalServerError)
 		return
 	}
@@ -238,6 +343,7 @@ func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request,
 	claims, err := t.extractClaimsFunc(tokenResponse.IDToken)
 	if err != nil {
 		t.logger.Errorf("Failed to extract claims during callback: %v", err)
+		t.clearOneTimeAuthState(session, req, rw)
 		t.sendErrorResponse(rw, req, "Authentication failed: Could not extract claims from token", http.StatusInternalServerError)
 		return
 	}
@@ -245,41 +351,57 @@ func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request,
 	nonceClaim, ok := claims["nonce"].(string)
 	if !ok || nonceClaim == "" {
 		t.logger.Error("Nonce claim missing in id_token during callback")
-		t.sendErrorResponse(rw, req, "Authentication failed: Nonce missing in token", http.StatusInternalServerError)
+		t.clearOneTimeAuthState(session, req, rw)
+		t.sendErrorResponse(rw, req, "Authentication failed: Nonce missing in token", http.StatusBadRequest)
 		return
 	}
 
 	sessionNonce := session.GetNonce()
 	if sessionNonce == "" {
 		t.logger.Error("Nonce not found in session during callback")
-		t.sendErrorResponse(rw, req, "Authentication failed: Nonce missing in session", http.StatusInternalServerError)
+		t.clearOneTimeAuthState(session, req, rw)
+		t.sendErrorResponse(rw, req, "Authentication failed: Nonce missing in session", http.StatusBadRequest)
 		return
 	}
 
 	if !constantTimeStringCompare(nonceClaim, sessionNonce) {
 		t.logger.Error("Nonce claim does not match session nonce during callback")
-		t.sendErrorResponse(rw, req, "Authentication failed: Nonce mismatch", http.StatusInternalServerError)
+		t.clearOneTimeAuthState(session, req, rw)
+		t.sendErrorResponse(rw, req, "Authentication failed: Nonce mismatch", http.StatusBadRequest)
 		return
 	}
 
 	// Extract user identifier from the configured claim (defaults to "email" for backward compatibility)
-	userIdentifier, _ := claims[t.userIdentifierClaim].(string)
+	userIdentifier, _ := claimScalarString(claims[t.userIdentifierClaim])
 	if userIdentifier == "" {
 		// Try "sub" as fallback since it's required by OIDC spec
 		if t.userIdentifierClaim != "sub" {
-			userIdentifier, _ = claims["sub"].(string)
+			userIdentifier, _ = claimScalarString(claims["sub"])
 		}
 		if userIdentifier == "" {
 			t.logger.Errorf("User identifier claim '%s' missing or empty in token during callback", t.userIdentifierClaim)
+			t.clearOneTimeAuthState(session, req, rw)
 			t.sendErrorResponse(rw, req, "Authentication failed: User identifier missing in token", http.StatusInternalServerError)
 			return
 		}
 		t.logger.Debugf("Configured claim '%s' not found, using 'sub' claim as fallback", t.userIdentifierClaim)
 	}
 
+	// Validate user authorization. When the identity is an email, require the
+	// IdP not to have explicitly flagged it as unverified — an unverified
+	// address must not satisfy an email/domain allowlist (see
+	// emailIdentityPermitted).
+	if !emailIdentityPermitted(userIdentifier, claims) {
+		t.logger.Errorf("User email not verified during callback, rejecting email-based authorization: %s", userIdentifier)
+		t.clearOneTimeAuthState(session, req, rw)
+		t.sendErrorResponse(rw, req, "Authentication failed: Email not verified", http.StatusForbidden)
+		return
+	}
+
 	// Validate user authorization
 	if !t.isAllowedUser(userIdentifier) {
 		t.logger.Errorf("User not authorized during callback: %s", userIdentifier)
+		t.clearOneTimeAuthState(session, req, rw)
 		t.sendErrorResponse(rw, req, "Authentication failed: User not authorized", http.StatusForbidden)
 		return
 	}
@@ -316,6 +438,8 @@ func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request,
 	}
 
 	t.logger.Debugf("Callback successful, redirecting to %s", redirectPath)
+	// no-store so the post-auth redirect isn't cached and replayed (R147).
+	rw.Header().Set("Cache-Control", "no-store")
 	http.Redirect(rw, req, redirectPath, http.StatusFound)
 }
 

bearer_auth.go

@@ -29,6 +29,7 @@ import (
 	"encoding/base64"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -93,6 +94,10 @@ const (
 type bearerError struct {
 	kind   bearerErrorKind
 	reason string
+	// retryAfter carries the actual remaining penalty when known (e.g. the
+	// per-IP penalty box), so writeBearerError emits the true value instead
+	// of the full configured penalty.
+	retryAfter time.Duration
 }
 
 func (e *bearerError) Error() string { return e.reason }
@@ -110,6 +115,32 @@ type joseHeader struct {
 	Typ string `json:"typ"`
 }
 
+// joseHeaderWellFormed reports whether token is structurally a JWT: exactly
+// two dot-separated segments whose header decodes as a JSON JOSE header.
+// It intentionally applies NO alg/kid policy (unlike parseBearerJOSEHeader)
+// so the JWT-vs-opaque routing gate classifies purely on structure: a
+// structurally-valid JWT with a disallowed alg stays on the JWT path
+// (where local policy rejects it), while an opaque token whose two dots
+// are coincidental falls through to opaque introspection (R166).
+func joseHeaderWellFormed(token string) bool {
+	dot := strings.IndexByte(token, '.')
+	if dot <= 0 {
+		return false
+	}
+	if strings.Count(token[dot+1:], ".") != 1 {
+		return false
+	}
+	raw, err := base64.RawURLEncoding.DecodeString(token[:dot])
+	if err != nil {
+		raw, err = base64.URLEncoding.DecodeString(token[:dot])
+		if err != nil {
+			return false
+		}
+	}
+	var hdr joseHeader
+	return json.Unmarshal(raw, &hdr) == nil
+}
+
 // parseBearerJOSEHeader decodes the first JWT segment for early alg/kid pinning.
 // Does not touch the payload or signature — those are the verifier's job.
 // Returns nil on success; *bearerError on rejection so the handler can map
@@ -153,19 +184,22 @@ func parseBearerJOSEHeader(token string) *bearerError {
 // header value, or "" if the rune is acceptable. Shared core of the bearer-path
 // identifier sanitizer and the cookie-path header claim sanitizer: rejects
 // control chars (CRLF/header injection), Unicode bidi-override runes (RTL
-// spoofing of admin UI / SIEM), and the delimiters , ; = (a comma in a group
-// name would inject extra entries into a comma-joined header).
+// spoofing of admin UI / SIEM), and the delimiters , ; = plus the bracketing
+// characters " { } — each of these in a group name / identifier would break a
+// downstream comma-joined list or a naive CSV/JSON-style parser consuming the
+// header (a comma would inject extra entries into a comma-joined header).
 func headerClaimRuneReason(r rune) string {
 	if reason := headerInjectionRuneReason(r); reason != "" {
 		return reason
 	}
-	// The , ; = delimiters are only unsafe for values placed into delimited or
-	// list contexts (a comma-joined header, or an identifier downstreams may
-	// split). They are valid in arbitrary single header values, so this stricter
-	// check is used for the cookie-path identifier and the group/role list, NOT
-	// for free-form templated header output (see headerValueReason).
-	if r == ',' || r == ';' || r == '=' {
-		return "delimiter character"
+	// The , ; = delimiters and the " { } bracketing chars are only unsafe for
+	// values placed into delimited or list contexts (a comma-joined header, or
+	// an identifier downstreams may split). They are valid in arbitrary single
+	// header values, so this stricter check is used for the cookie-path
+	// identifier and the group/role list, NOT for free-form templated header
+	// output (see headerValueReason).
+	if r == ',' || r == ';' || r == '=' || r == '"' || r == '{' || r == '}' {
+		return "delimiter or bracketing character"
 	}
 	return ""
 }
@@ -270,11 +304,12 @@ func resolveBearerIdentifier(claims map[string]interface{}, claimName string) (s
 	if !ok {
 		return "", newBearerError(bearerErrInvalidIdentifier, fmt.Sprintf("missing claim %q", claimName))
 	}
-	str, ok := raw.(string)
-	if !ok {
-		return "", newBearerError(bearerErrInvalidIdentifier, fmt.Sprintf("claim %q not a string", claimName))
+	// Accept scalar numbers (e.g. a numeric sub) by stringifying them,
+	// so a numeric identifier claim doesn't 401 a valid principal.
+	if s, isScalar := claimScalarString(raw); isScalar {
+		return s, nil
 	}
-	return str, nil
+	return "", newBearerError(bearerErrInvalidIdentifier, fmt.Sprintf("claim %q is not a scalar string or number", claimName))
 }
 
 // enforceMultiAudienceAzp implements the spec hardening: when aud is a
@@ -358,6 +393,10 @@ type bearerFailureEntry struct {
 	count          int
 }
 
+// defaultBearerEntrySweepThreshold is the map size above which recordFailure
+// sweeps stale entries, bounding memory under a flood of distinct source IPs.
+const defaultBearerEntrySweepThreshold = 1024
+
 func newBearerFailureTracker(threshold int, window, penalty time.Duration) *bearerFailureTracker {
 	if threshold <= 0 {
 		threshold = 20
@@ -404,6 +443,18 @@ func (b *bearerFailureTracker) recordFailure(ip string) {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 	now := time.Now()
+	// Bound per-IP map growth (R117): entries for source IPs that fail once
+	// and never return were never removed. Sweep stale entries (no active
+	// penalty box, too old to matter) once the map grows past a nominal
+	// size, keeping steady-state memory bounded.
+	if len(b.entries) > defaultBearerEntrySweepThreshold {
+		cutoff := now.Add(-(b.window + b.penalty))
+		for k, e := range b.entries {
+			if e.penaltyUntil.Before(cutoff) {
+				delete(b.entries, k)
+			}
+		}
+	}
 	e, ok := b.entries[ip]
 	if !ok || now.Sub(e.firstFailureAt) > b.window {
 		e = &bearerFailureEntry{firstFailureAt: now}
@@ -520,7 +571,10 @@ func (t *TraefikOidc) writeBearerError(rw http.ResponseWriter, req *http.Request
 	case bearerErrThrottled:
 		status = http.StatusTooManyRequests
 		body = "Too Many Requests"
-		retryAfter = t.bearerFailurePenalty
+		retryAfter = err.retryAfter
+		if retryAfter <= 0 {
+			retryAfter = t.bearerFailurePenalty
+		}
 	case bearerErrIntrospectionUnavailable:
 		status = http.StatusServiceUnavailable
 		body = "Service Unavailable"
@@ -535,6 +589,10 @@ func (t *TraefikOidc) writeBearerError(rw http.ResponseWriter, req *http.Request
 	if retryAfter > 0 {
 		rw.Header().Set("Retry-After", fmt.Sprintf("%d", int(retryAfter.Seconds())))
 	}
+	// Auth-rejection responses must never be cached (R101 contract): a
+	// cached 429/401 could be replayed to a client well after the
+	// penalty box expired or the session recovered.
+	rw.Header().Set("Cache-Control", "no-store")
 	rw.Header().Set("Content-Type", "text/plain; charset=utf-8")
 	rw.WriteHeader(status)
 	_, _ = rw.Write([]byte(body)) // Safe to ignore: best-effort error body write
@@ -553,12 +611,11 @@ func (t *TraefikOidc) handleBearerRequest(rw http.ResponseWriter, req *http.Requ
 	ip := clientIPForBearer(req)
 
 	if blocked, retryAfter := t.bearerFailureTracker.blocked(ip); blocked {
+		// Carry the actual remaining penalty (diverges from the configured
+		// default on clock-skew, partial-window expiry) so writeBearerError
+		// emits the true Retry-After rather than the full penalty.
 		throttled := newBearerError(bearerErrThrottled, "ip in penalty box")
-		// Preserve the actual retry-after even if it diverged from the
-		// configured default (clock-skew, partial-window expiry).
-		if retryAfter > 0 {
-			rw.Header().Set("Retry-After", fmt.Sprintf("%d", int(retryAfter.Seconds())))
-		}
+		throttled.retryAfter = retryAfter
 		t.writeBearerError(rw, req, throttled)
 		return
 	}
@@ -574,12 +631,51 @@ func (t *TraefikOidc) handleBearerRequest(rw http.ResponseWriter, req *http.Requ
 		t.writeBearerError(rw, req, newBearerError(bearerErrInvalidToken, "token exceeds max length"))
 		return
 	}
-	if strings.Count(token, ".") != 2 {
+	// Determine whether this is genuinely a JWT. RFC 7662 token
+	// introspection covers opaque access tokens; when the operator
+	// requires live introspection (requireTokenIntrospection, whose
+	// documented purpose is exactly opaque-token support via
+	// client_secret_basic), introspect the opaque token on the bearer
+	// path instead of rejecting it — the session path already does
+	// (validateOpaqueToken). Previously the JWT-shape gate ran before
+	// the introspection branch, so every opaque token got a 401 even
+	// with introspection on (R159).
+	//
+	// A token is only treated as a JWT when it has exactly two dots AND
+	// its header actually parses as a JOSE header. Dot count alone is
+	// insufficient: an opaque token that coincidentally contains exactly
+	// two dots used to be routed onto the JWT path and rejected even
+	// under requireTokenIntrospection (header parse would fail) — it must
+	// instead be introspected like any other opaque token (R166).
+	isJWT := joseHeaderWellFormed(token)
+	if !isJWT {
+		if t.requireTokenIntrospection {
+			p, bErr := t.buildPrincipalFromOpaqueIntrospection(token)
+			if bErr != nil {
+				if bErr.kind != bearerErrIntrospectionUnavailable {
+					t.bearerFailureTracker.recordFailure(ip)
+				}
+				t.writeBearerError(rw, req, bErr)
+				return
+			}
+			t.bearerFailureTracker.recordSuccess(ip)
+			if t.logger != nil {
+				t.logger.Debugf("bearer auth success (introspected opaque): identifier_hash=%s path=%s",
+					hashIdentifierForLog(p.Identifier), req.URL.Path)
+			}
+			t.forwardAuthorized(rw, req, p)
+			return
+		}
 		t.bearerFailureTracker.recordFailure(ip)
-		t.writeBearerError(rw, req, newBearerError(bearerErrInvalidToken, "token is not a 3-segment JWT"))
+		t.writeBearerError(rw, req, newBearerError(bearerErrInvalidToken, "token is not a valid JWT"))
 		return
 	}
 
+	// Structurally a JWT: enforce the alg/kid policy EARLY (before the
+	// cached fast-path in buildPrincipalFromBearerToken can short-circuit
+	// on a prior positive verdict). Without this pin an alg=none or
+	// oversized-kid token that had been cached as verified would sail
+	// through without re-checking.
 	if bErr := parseBearerJOSEHeader(token); bErr != nil {
 		t.bearerFailureTracker.recordFailure(ip)
 		t.writeBearerError(rw, req, bErr)
@@ -588,7 +684,13 @@ func (t *TraefikOidc) handleBearerRequest(rw http.ResponseWriter, req *http.Requ
 
 	p, bErr := t.buildPrincipalFromBearerToken(token)
 	if bErr != nil {
-		t.bearerFailureTracker.recordFailure(ip)
+		// Count only authentication failures (401/403) toward the per-IP
+		// throttle. An introspection outage (503) is infrastructure, not a
+		// client failure; recording it would trip a 429 penalty that a
+		// single success can't clear even after the endpoint recovers.
+		if bErr.kind != bearerErrIntrospectionUnavailable {
+			t.bearerFailureTracker.recordFailure(ip)
+		}
 		t.writeBearerError(rw, req, bErr)
 		return
 	}
@@ -629,7 +731,9 @@ func (t *TraefikOidc) buildPrincipalFromBearerToken(token string) (*principal, *
 		return nil, newBearerError(bearerErrInvalidToken, "token_use=id rejected")
 	}
 
-	if bErr := enforceMultiAudienceAzp(claims, t.clientID); bErr != nil {
+	// Snapshot clientID under metadataMu: DCR rewrites it at runtime (R137).
+	clientID, _, _, _, _ := t.clientCredentials()
+	if bErr := enforceMultiAudienceAzp(claims, clientID); bErr != nil {
 		return nil, bErr
 	}
 	if bErr := enforceIatAge(claims, t.maxTokenAge); bErr != nil {
@@ -642,6 +746,25 @@ func (t *TraefikOidc) buildPrincipalFromBearerToken(token string) (*principal, *
 		}
 	}
 
+	// Honor IdP-initiated (backchannel/front-channel) logout. The cookie
+	// path re-checks sessionInvalidationCache on every request; the bearer
+	// path previously did not, so a still-cryptographically-valid access
+	// token for a logged-out subject kept returning 200 (and, with
+	// requireTokenIntrospection, a cached positive verdict extended the
+	// stale window). Reject here, mirroring the cookie path: use the
+	// token's iat as its creation time so a token issued before the
+	// logout is invalidated, while a legitimately freshly-issued token
+	// (iat after logout) still passes (R146).
+	subjectForInvalidation, _ := claims["sub"].(string)
+	sidForInvalidation, _ := claims["sid"].(string)
+	createdAt := time.Now()
+	if iat, ok := claims["iat"].(float64); ok {
+		createdAt = time.Unix(int64(iat), 0)
+	}
+	if t.isSessionInvalidated(sidForInvalidation, subjectForInvalidation, createdAt) {
+		return nil, newBearerError(bearerErrInvalidToken, "session has been invalidated (logout)")
+	}
+
 	rawIdentifier, bErr := resolveBearerIdentifier(claims, t.bearerIdentifierClaim)
 	if bErr != nil {
 		return nil, bErr
@@ -652,7 +775,7 @@ func (t *TraefikOidc) buildPrincipalFromBearerToken(token string) (*principal, *
 	}
 
 	subject, _ := claims["sub"].(string)
-	clientID, _ := claims["azp"].(string)
+	clientID, _ = claims["azp"].(string)
 	if clientID == "" {
 		clientID, _ = claims["client_id"].(string)
 	}
@@ -667,6 +790,62 @@ func (t *TraefikOidc) buildPrincipalFromBearerToken(token string) (*principal, *
 	}, nil
 }
 
+// buildPrincipalFromOpaqueIntrospection authenticates a bearer access
+// token that has no JWT shape by live RFC 7662 introspection, and builds
+// a principal whose identifier is the introspected subject. It mirrors
+// introspectOnBearerPath's classification (active, token_type, expiry,
+// audience) and binds the compliant subject. Only used on the bearer
+// path when requireTokenIntrospection is enabled (R159).
+func (t *TraefikOidc) buildPrincipalFromOpaqueIntrospection(token string) (*principal, *bearerError) {
+	resp, err := t.introspectToken(token)
+	if err != nil {
+		var httpErr *HTTPError
+		if errors.As(err, &httpErr) && httpErr.StatusCode >= 400 && httpErr.StatusCode < 500 {
+			return nil, newBearerError(bearerErrTokenInactive, fmt.Sprintf("introspection reports token inactive (HTTP %d)", httpErr.StatusCode))
+		}
+		return nil, newBearerError(bearerErrIntrospectionUnavailable, "introspection failed: "+err.Error())
+	}
+	if !resp.Active {
+		return nil, newBearerError(bearerErrTokenInactive, "introspection reports token inactive")
+	}
+	// Mirror introspectOnBearerPath (R149): reject a definite non-access
+	// token_type (e.g. refresh_token); accept "access_token" and "Bearer".
+	if resp.TokenType != "" && resp.TokenType != "access_token" && resp.TokenType != "Bearer" {
+		return nil, newBearerError(bearerErrTokenInactive, "introspection token_type is not a bearer access token")
+	}
+	if resp.Exp > 0 && time.Now().After(time.Unix(resp.Exp, 0)) {
+		return nil, newBearerError(bearerErrTokenInactive, "introspection reports token expired")
+	}
+	// Audience gate when a distinct API audience is configured.
+	clientID, _, _, audience, _ := t.clientCredentials()
+	if audience != "" && audience != clientID {
+		if resp.Aud == nil || verifyAudience(resp.Aud, audience) != nil {
+			return nil, newBearerError(bearerErrTokenInactive, "introspection audience mismatch")
+		}
+	}
+	id := resp.Sub
+	if id == "" {
+		id = resp.Username
+	}
+	if id == "" {
+		return nil, newBearerError(bearerErrInvalidToken, "introspection response has no subject or username")
+	}
+	claims := map[string]interface{}{}
+	if resp.Sub != "" {
+		claims["sub"] = resp.Sub
+	}
+	if resp.Username != "" {
+		claims["username"] = resp.Username
+	}
+	return &principal{
+		Claims:      claims,
+		Identifier:  id,
+		Subject:     resp.Sub,
+		AccessToken: token,
+		Source:      sourceBearer,
+	}, nil
+}
+
 // introspectOnBearerPath calls the existing RFC 7662 introspector when the
 // operator demands real-time revocation. Distinguishes "token revoked" (401)
 // from "endpoint unavailable" (503) so transient infra failures don't look
@@ -674,10 +853,55 @@ func (t *TraefikOidc) buildPrincipalFromBearerToken(token string) (*principal, *
 func (t *TraefikOidc) introspectOnBearerPath(token string) *bearerError {
 	resp, err := t.introspectToken(token)
 	if err != nil {
+		// A definitive 4xx from the introspection endpoint (e.g. 401 for
+		// an unknown/revoked token) is a credential failure, not an infra
+		// outage — don't downgrade it to "unavailable" (R156).
+		var httpErr *HTTPError
+		if errors.As(err, &httpErr) && httpErr.StatusCode >= 400 && httpErr.StatusCode < 500 {
+			return newBearerError(bearerErrTokenInactive, fmt.Sprintf("introspection reports token inactive (HTTP %d)", httpErr.StatusCode))
+		}
 		return newBearerError(bearerErrIntrospectionUnavailable, "introspection failed: "+err.Error())
 	}
 	if !resp.Active {
 		return newBearerError(bearerErrTokenInactive, "introspection reports token inactive")
 	}
+	// Mirror the session path (validateOpaqueToken): an opaque-or-any
+	// token whose RFC 7662 token_type classifies it as a refresh token
+	// must not be honored as a bearer access token (R149). Only reject on
+	// a definite non-access match; compliant providers may omit it. RFC
+	// 7662's token_type is the RFC 6749 token type, whose value for an
+	// access token is "Bearer" (RFC 6750) — accept both spellings
+	// providers use (R156).
+	if resp.TokenType != "" && resp.TokenType != "access_token" && resp.TokenType != "Bearer" {
+		return newBearerError(bearerErrTokenInactive, "introspection token_type is not a bearer access token")
+	}
+	// Mirror the session path (validateOpaqueToken): an active but
+	// already-expired result must not pass. The positive-only cache is
+	// capped by time-until-exp when Exp is present, but a provider
+	// returning active=1 past exp would otherwise let the token pass on
+	// the bearer path while the identical token is rejected on the
+	// session path.
+	if resp.Exp > 0 {
+		expTime := time.Unix(resp.Exp, 0)
+		if time.Now().After(expTime) {
+			return newBearerError(bearerErrTokenInactive, "introspection reports token expired")
+		}
+	}
+	// Mirror the session path (validateOpaqueToken): when a distinct API
+	// audience is configured (audience != clientID), the introspection
+	// response MUST carry a matching audience. Fail closed on a missing or
+	// mismatched aud, otherwise a token minted for a different audience
+	// would pass the bearer path while the identical token is rejected on
+	// the session path. aud may be a single string or an array (RFC 7662).
+	// (R143)
+	clientID, _, _, audience, _ := t.clientCredentials()
+	if audience != "" && audience != clientID {
+		if resp.Aud == nil {
+			return newBearerError(bearerErrTokenInactive, "introspection reports no audience")
+		}
+		if err := verifyAudience(resp.Aud, audience); err != nil {
+			return newBearerError(bearerErrTokenInactive, "introspection audience mismatch")
+		}
+	}
 	return nil
 }

client_assertion.go

@@ -95,9 +95,18 @@ func NewClientAssertionSigner(pemBytes []byte, alg, kid string) (*ClientAssertio
 func validateAlgKeyMatch(alg string, key crypto.PrivateKey) error {
 	switch alg[0] {
 	case 'R', 'P': // RS* or PS*
-		if _, ok := key.(*rsa.PrivateKey); !ok {
+		rsaKey, ok := key.(*rsa.PrivateKey)
+		if !ok {
 			return fmt.Errorf("alg %q requires an RSA key, got %T", alg, key)
 		}
+		// RFC 7518 §3.3: RS*/PS* MUST use a key of 2048 bits or larger.
+		// A smaller key signs locally but conformant IdPs (Entra, Okta,
+		// Keycloak) reject it, so every exchange/refresh/revocation fails
+		// invalid_client at runtime — better to fail at construction
+		// (R135).
+		if rsaKey.N.BitLen() < 2048 {
+			return fmt.Errorf("alg %q requires an RSA key of at least 2048 bits, got %d", alg, rsaKey.N.BitLen())
+		}
 	case 'E': // ES*
 		ecKey, ok := key.(*ecdsa.PrivateKey)
 		if !ok {
@@ -142,6 +151,14 @@ func (s *ClientAssertionSigner) Sign(audience, clientID string) (string, error)
 
 	now := nowFn()
 
+	// RFC 7523 §3: aud must be the token (or introspection/revocation)
+	// endpoint URL. An empty audience yields a client_assertion with
+	// "aud":"" that the IdP will reject, so fail fast with a clear
+	// error rather than minting a useless token (R150).
+	if audience == "" {
+		return "", fmt.Errorf("client assertion audience must not be empty")
+	}
+
 	// 16 random bytes as lowercase hex for jti uniqueness.
 	jtiBytes := make([]byte, 16)
 	if _, err := io.ReadFull(rander, jtiBytes); err != nil {
@@ -312,6 +329,3 @@ func buildClientAssertionSignerFromConfig(config *Config) (*ClientAssertionSigne
 
 	return NewClientAssertionSigner(pemBytes, alg, config.ClientAssertionKeyID)
 }
-
-
-

helpers.go

@@ -107,10 +107,13 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, code
 	data := url.Values{
 		"grant_type": {grantType},
 	}
+	// Snapshot client credentials under metadataMu: DCR rewrites clientID/
+	// clientSecret/audience at runtime (R137).
+	clientID, clientSecret, clientAuthMethod, _, clientAssertion := t.clientCredentials()
 	// client_id is sent in the body for every method except client_secret_basic,
 	// where it is carried in the Authorization header per RFC 6749 §2.3.1.
-	if t.clientAuthMethod != "client_secret_basic" || t.clientAssertion != nil {
-		data.Set("client_id", t.clientID)
+	if clientAuthMethod != "client_secret_basic" || clientAssertion != nil {
+		data.Set("client_id", clientID)
 	}
 
 	if grantType == "authorization_code" {
@@ -148,17 +151,17 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, code
 	t.metadataMu.RUnlock()
 
 	useBasicAuth := false
-	if t.clientAssertion != nil {
-		assertion, err := t.clientAssertion.Sign(tokenURL, t.clientID)
+	if clientAssertion != nil {
+		assertion, err := clientAssertion.Sign(tokenURL, clientID)
 		if err != nil {
 			return nil, fmt.Errorf("failed to sign client assertion: %w", err)
 		}
 		data.Set("client_assertion_type", "urn:ietf:params:oauth:client-assertion-type:jwt-bearer")
 		data.Set("client_assertion", assertion)
-	} else if t.clientAuthMethod == "client_secret_basic" {
+	} else if clientAuthMethod == "client_secret_basic" {
 		useBasicAuth = true
 	} else {
-		data.Set("client_secret", t.clientSecret)
+		data.Set("client_secret", clientSecret)
 	}
 
 	req, err := http.NewRequestWithContext(ctx, "POST", tokenURL, strings.NewReader(data.Encode())) //nolint:gosec // tokenURL is the operator-trusted discovery endpoint (metadataMu)
@@ -167,7 +170,7 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, code
 	}
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 	if useBasicAuth {
-		setOAuthBasicAuth(req, t.clientID, t.clientSecret)
+		setOAuthBasicAuth(req, clientID, clientSecret)
 	}
 
 	resp, err := client.Do(req) //nolint:gosec // req above targets the trusted tokenURL
@@ -182,7 +185,14 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, code
 	if resp.StatusCode != http.StatusOK {
 		limitReader := io.LimitReader(resp.Body, 1024*10)
 		bodyBytes, _ := io.ReadAll(limitReader) // Safe to ignore: reading error body for diagnostics
-		return nil, fmt.Errorf("token endpoint returned status %d: %s", resp.StatusCode, string(bodyBytes))
+		// Return a *HTTPError so the retry executor's isRetryableError can
+		// classify transient 5xx/429 responses and actually retry (R118).
+		// A plain error here made the 5xx/429 retry branch dead in
+		// production — every token-endpoint status was treated as permanent.
+		return nil, &HTTPError{
+			StatusCode: resp.StatusCode,
+			Message:    fmt.Sprintf("token endpoint returned status %d: %s", resp.StatusCode, string(bodyBytes)),
+		}
 	}
 
 	var tokenResponse TokenResponse
@@ -192,6 +202,16 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, code
 		return nil, fmt.Errorf("failed to decode token response: %w", err)
 	}
 
+	// RFC 6749 §5.1: a token response MUST include an access_token. A 200
+	// that omitted it is a protocol violation, not a success — treat it as an
+	// error here so no caller authenticates with a blank token (R158).
+	// Previously this seam returned success with an empty access_token and
+	// each caller had to re-check "AccessToken == \"\"", which several
+	// paths missed.
+	if tokenResponse.AccessToken == "" {
+		return nil, fmt.Errorf("token endpoint returned 200 without an access_token (RFC 6749 §5.1)")
+	}
+
 	return &tokenResponse, nil
 }
 
@@ -204,6 +224,17 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, code
 // Returns:
 //   - *TokenResponse: New token set from the authorization server
 //   - An error if the refresh operation fails
+//
+// redactToken returns a short, stable hash of a token credential suitable for
+// debug logging without leaking the credential itself (R138).
+func redactToken(token string) string {
+	if token == "" {
+		return "(empty)"
+	}
+	sum := sha256.Sum256([]byte(token))
+	return fmt.Sprintf("%x", sum[:4])
+}
+
 func (t *TraefikOidc) getNewTokenWithRefreshToken(refreshToken string) (*TokenResponse, error) {
 	ctx := context.Background()
 
@@ -218,7 +249,8 @@ func (t *TraefikOidc) getNewTokenWithRefreshToken(refreshToken string) (*TokenRe
 		return nil, fmt.Errorf("failed to refresh token: %w", err)
 	}
 
-	t.logger.Debugf("Token response: %+v", tokenResponse)
+	t.logger.Debugf("Refresh token response: token_type=%s expires_in=%d access_token=%s",
+		tokenResponse.TokenType, tokenResponse.ExpiresIn, redactToken(tokenResponse.AccessToken))
 	return tokenResponse, nil
 }
 
@@ -399,6 +431,20 @@ func (t *TraefikOidc) handleLogout(rw http.ResponseWriter, req *http.Request) {
 		}
 	}
 
+	// Best-effort provider-side revocation (single logout): the local
+	// blacklist only stops reuse in-process, but a token captured before
+	// logout (e.g. a bearer-mode access token or the refresh token) stays
+	// valid at the IdP and a captured refresh token could keep minting new
+	// tokens. Revoke both access and refresh tokens at the provider when a
+	// revocation endpoint is available; ignore errors (the endpoint may be
+	// absent or the provider already cleaned up on the end-session call).
+	if accessToken != "" {
+		_ = t.RevokeTokenWithProvider(accessToken, "access_token")
+	}
+	if refreshToken != "" {
+		_ = t.RevokeTokenWithProvider(refreshToken, "refresh_token")
+	}
+
 	postLogoutRedirectURI := t.postLogoutRedirectURI
 	// localRedirect is used when there is no provider end-session endpoint and
 	// the plugin redirects the browser itself. It must never be an absolute URL
@@ -437,10 +483,15 @@ func (t *TraefikOidc) handleLogout(rw http.ResponseWriter, req *http.Request) {
 			http.Error(rw, "Logout error", http.StatusInternalServerError)
 			return
 		}
+		// Logout redirects must never be cached: a heuristic-caching proxy
+		// replaying the 302 would re-trigger logout for an already
+		// logged-out session (R147 cache-directive contract).
+		rw.Header().Set("Cache-Control", "no-store")
 		http.Redirect(rw, req, logoutURL, http.StatusFound)
 		return
 	}
 
+	rw.Header().Set("Cache-Control", "no-store")
 	http.Redirect(rw, req, localRedirect, http.StatusFound)
 }
 

jwt.go

@@ -26,8 +26,6 @@ var (
 	replayCache CacheInterface
 	// shardedReplayCache is the new high-performance sharded cache for replay detection
 	shardedReplayCache *ShardedCache
-	// replayCacheOnce ensures the replay cache is initialized only once
-	replayCacheOnce sync.Once
 	// replayCacheCleanupWG waits for cleanup goroutine to finish
 	replayCacheCleanupWG sync.WaitGroup
 	// replayCacheCancel cancels the cleanup context
@@ -39,21 +37,23 @@ var (
 // initReplayCache initializes the JWT replay protection cache with bounded size.
 // Uses a sharded cache design with 64 shards for reduced lock contention under high load.
 // The cache is bounded to 10,000 entries to prevent unbounded memory growth.
-// This function uses sync.Once to ensure thread-safe single initialization.
+// Lazy creation is guarded entirely by replayCacheMu (a plain sync.Once would
+// not re-arm after cleanup resets it, and the previous Once re-assignment raced
+// with init under -race). cleanupReplayCache nil's the fields under the same
+// lock, so this either creates anew (after a cleanup) or is a cheap no-op.
 func initReplayCache() {
-	replayCacheOnce.Do(func() {
-		// Hold mutex during initialization to synchronize with cleanup goroutine
-		replayCacheMu.Lock()
-		defer replayCacheMu.Unlock()
+	replayCacheMu.Lock()
+	defer replayCacheMu.Unlock()
 
-		// Create sharded cache with 64 shards for reduced contention
+	if shardedReplayCache == nil {
+		// Create sharded cache with 64 shards for reduced lock contention
 		// Under 500 req/sec, this reduces lock contention by ~64x compared to single mutex
 		shardedReplayCache = NewShardedCache(64, 10000)
 
 		// Also initialize legacy cache for backward compatibility
 		replayCache = NewCache()
 		replayCache.SetMaxSize(10000)
-	})
+	}
 }
 
 // cleanupReplayCache performs graceful shutdown of the replay cache system.
@@ -61,17 +61,12 @@ func initReplayCache() {
 // and properly closes the cache to ensure proper cleanup during shutdown.
 func cleanupReplayCache() {
 	replayCacheCleanupMu.Lock()
-	shouldWait := replayCacheCancel != nil
 	if replayCacheCancel != nil {
 		replayCacheCancel()
 		replayCacheCancel = nil
 	}
 	replayCacheCleanupMu.Unlock()
-
-	// Only wait if there was a cleanup routine running
-	if shouldWait {
-		replayCacheCleanupWG.Wait()
-	}
+	replayCacheCleanupWG.Wait()
 
 	replayCacheMu.Lock()
 	defer replayCacheMu.Unlock()
@@ -87,8 +82,16 @@ func cleanupReplayCache() {
 		replayCache.Close()
 		replayCache = nil
 	}
+}
 
-	replayCacheOnce = sync.Once{}
+// replayCacheKey namespaces a JTI by its issuer before it is stored in the
+// process-global replay cache. JTI uniqueness is guaranteed only within a
+// single issuer's namespace; many Traefik routers share this one global
+// cache across different OIDC providers, so a bare jti would let two
+// providers' legitimately-colliding JTIs map to the same entry (false
+// replay) and silently overwrite each other (R142).
+func replayCacheKey(issuer, jti string) string {
+	return issuer + "\x00" + jti
 }
 
 // getReplayCacheStats returns statistics about the replay cache state.
@@ -96,9 +99,14 @@ func cleanupReplayCache() {
 //   - size: Current number of entries in the cache
 //   - maxSize: Maximum allowed entries (10,000)
 func getReplayCacheStats() (size int, maxSize int) {
-	// Use sharded cache if available (no mutex needed due to internal sharding)
-	if shardedReplayCache != nil {
-		return shardedReplayCache.Size(), 10000
+	// Use sharded cache if available (no mutex needed due to internal sharding).
+	// Guard the singleton read because cleanupReplayCache nils it under the
+	// write lock.
+	replayCacheMu.RLock()
+	sc := shardedReplayCache
+	replayCacheMu.RUnlock()
+	if sc != nil {
+		return sc.Size(), 10000
 	}
 
 	// Fall back to legacy cache
@@ -281,13 +289,12 @@ func parseJWT(tokenString string) (*JWT, error) {
 		return nil, fmt.Errorf("invalid JWT format: failed to decode signature: %v", err)
 	}
 
-	// Reuse the signature buffer if it's large enough, otherwise allocate
-	if cap(jwtBuf.Signature) >= n {
-		jwt.Signature = jwtBuf.Signature[:n:n] // Use slice trick to prevent aliasing
-	} else {
-		jwt.Signature = make([]byte, n)
-		copy(jwt.Signature, jwtBuf.Signature[:n])
-	}
+	// Copy the signature out of the pooled buffer. Borrowing it with
+	// [:(n):(n)] still shares the backing array, which the pool recycles
+	// and truncates on the next GetJWTBuffer — mutating this caller's
+	// slice after the fact (R156).
+	jwt.Signature = make([]byte, n)
+	copy(jwt.Signature, jwtBuf.Signature[:n])
 
 	return jwt, nil
 }
@@ -342,12 +349,13 @@ func (j *JWT) Verify(issuerURL, expectedAudience string, skipReplayCheck ...bool
 		return err
 	}
 
-	iat, ok := claims["iat"].(float64)
-	if !ok {
-		return fmt.Errorf("missing or invalid 'iat' claim")
-	}
-	if err := verifyIssuedAt(iat); err != nil {
-		return err
+	// iat is OPTIONAL per RFC 7519 §4.1.6; only validate when present.
+	// Hard-requiring it here also rejected otherwise-valid access and
+	// logout tokens whose provider omits iat.
+	if iat, ok := claims["iat"].(float64); ok {
+		if err := verifyIssuedAt(iat); err != nil {
+			return err
+		}
 	}
 
 	if nbf, ok := claims["nbf"].(float64); ok {
@@ -371,6 +379,12 @@ func (j *JWT) Verify(issuerURL, expectedAudience string, skipReplayCheck ...bool
 			expTime = time.Now().Add(10 * time.Minute)
 		}
 		duration := time.Until(expTime)
+		// A token is accepted until exp + ClockSkewToleranceFuture (see
+		// verifyExpiration), so the replay entry must live that long too —
+		// otherwise in the (exp, exp+skew] window the entry has expired
+		// and been swept and the same token is re-accepted as fresh
+		// (R179).
+		duration += ClockSkewToleranceFuture
 		if duration <= 0 {
 			// Expired token: no replay window worth recording, so nothing to do.
 			goto replayDone
@@ -386,18 +400,26 @@ func (j *JWT) Verify(issuerURL, expectedAudience string, skipReplayCheck ...bool
 		replayCacheMu.RLock()
 		sc := shardedReplayCache
 		if sc != nil {
-			if !sc.SetIfAbsent(jtiValue, true, duration) {
+			if !sc.SetIfAbsent(replayCacheKey(issuerURL, jtiValue), true, duration) {
 				replayCacheMu.RUnlock()
 				return fmt.Errorf("token replay detected (jti: %s)", jtiValue)
 			}
 			replayCacheMu.RUnlock()
 		} else {
-			// Fall back to legacy cache (should rarely happen). Hold the
-			// mutex across the get+set so the record is atomic there too.
+			// Fall back to legacy cache (should rarely happen). Release the
+			// read lock before taking the write lock: RWMutex is not
+			// reentrant, so Lock() here while still holding RLock()
+			// self-deadlocks (R156). Guard the cache for nil — it is
+			// cleared alongside shardedReplayCache by cleanupReplayCache.
+			replayCacheMu.RUnlock()
 			replayCacheMu.Lock()
-			_, exists := replayCache.Get(jtiValue)
-			if !exists && replayCache != nil {
-				replayCache.Set(jtiValue, true, duration)
+			rk := replayCacheKey(issuerURL, jtiValue)
+			exists := false
+			if replayCache != nil {
+				_, exists = replayCache.Get(rk)
+				if !exists {
+					replayCache.Set(rk, true, duration)
+				}
 			}
 			replayCacheMu.Unlock()
 			if exists {

logout.go

@@ -100,7 +100,10 @@ func (t *TraefikOidc) handleBackchannelLogout(rw http.ResponseWriter, req *http.
 	t.logger.Infof("Backchannel logout: successfully invalidated session (sid=%s, sub=%s)",
 		claims.SessionID, claims.Subject)
 
-	// Return 200 OK with empty body per spec
+	// Return 200 OK with empty body per spec; mark it non-cacheable so a
+	// proxy cannot replay a stale logout acknowledgement (R147 contract).
+	rw.Header().Set("Cache-Control", "no-store")
+	rw.Header().Set("Content-Type", "text/plain; charset=utf-8")
 	rw.WriteHeader(http.StatusOK)
 }
 
@@ -291,18 +294,27 @@ func (t *TraefikOidc) validateLogoutToken(tokenString string) (*LogoutTokenClaim
 
 // validateLogoutTokenAudience checks if the logout token audience contains our client_id
 func (t *TraefikOidc) validateLogoutTokenAudience(aud interface{}) bool {
+	// t.clientID is mutated at runtime by the DCR path
+	// (performDynamicClientRegistration, under metadataMu). Read it under
+	// the same lock as every other credential field (issuer, jwksURL) so a
+	// backchannel-logout token validated concurrent with client re-issuance
+	// does not race the write.
+	t.metadataMu.RLock()
+	clientID := t.clientID
+	t.metadataMu.RUnlock()
+
 	switch v := aud.(type) {
 	case string:
-		return v == t.clientID
+		return v == clientID
 	case []interface{}:
 		for _, a := range v {
-			if s, ok := a.(string); ok && s == t.clientID {
+			if s, ok := a.(string); ok && s == clientID {
 				return true
 			}
 		}
 	case []string:
 		for _, a := range v {
-			if a == t.clientID {
+			if a == clientID {
 				return true
 			}
 		}
@@ -342,6 +354,17 @@ func (t *TraefikOidc) verifyLogoutTokenSignature(jwt *JWT, tokenString string) e
 	}
 
 	if err := verifySignatureWithKey(tokenString, pubKey, alg); err != nil {
+		// The signature failed against the (possibly stale) cached key. The
+		// provider may have rotated its signing keys in place, reusing the
+		// same kid (R109): refresh the JWKS once and retry before failing.
+		// Without this a logout token signed with an in-place-rotated key is
+		// rejected for up to the JWKS cache TTL, leaving the user's session
+		// alive after the IdP logged them out (R130).
+		if freshKey, ferr := t.jwkCache.getPublicKeyFresh(context.Background(), jwksURL, kid, t.httpClient); ferr == nil {
+			if verr := verifySignatureWithKey(tokenString, freshKey, alg); verr == nil {
+				return nil
+			}
+		}
 		return fmt.Errorf("signature verification failed: %w", err)
 	}
 
@@ -402,6 +425,29 @@ func (t *TraefikOidc) invalidateSession(sid, sub string) error {
 //
 // Returns:
 //   - true if the session has been invalidated, false otherwise
+//
+// sessionInvalidationTime extracts the invalidation timestamp from a cache
+// value regardless of backend storage semantics. The in-memory cache returns
+// the raw int64 we stored; serializing backends (e.g. Redis) JSON round-trip
+// numbers, so Get yields a float64. Accepting both keeps backchannel/front-
+// channel logout functional in multi-instance (distributed) deployments;
+// previously the strict int64 assertion silently returned false there.
+func sessionInvalidationTime(val interface{}) (int64, bool) {
+	switch v := val.(type) {
+	case int64:
+		return v, true
+	case float64:
+		return int64(v), true
+	case json.Number:
+		n, err := v.Int64()
+		if err != nil {
+			return 0, false
+		}
+		return n, true
+	}
+	return 0, false
+}
+
 func (t *TraefikOidc) isSessionInvalidated(sid, sub string, sessionCreatedAt time.Time) bool {
 	if t.sessionInvalidationCache == nil {
 		return false
@@ -414,7 +460,7 @@ func (t *TraefikOidc) isSessionInvalidated(sid, sub string, sessionCreatedAt tim
 	if sid != "" {
 		key := t.buildSessionInvalidationKey("sid", sid)
 		if val, found := t.sessionInvalidationCache.Get(key); found {
-			if invalidatedAt, ok := val.(int64); ok {
+			if invalidatedAt, ok := sessionInvalidationTime(val); ok {
 				// Session was invalidated at or after it was created
 				invalidationTime := time.Unix(invalidatedAt, 0)
 				if !invalidationTime.Before(sessionCreatedAtSec) {
@@ -429,7 +475,7 @@ func (t *TraefikOidc) isSessionInvalidated(sid, sub string, sessionCreatedAt tim
 	if sub != "" {
 		key := t.buildSessionInvalidationKey("sub", sub)
 		if val, found := t.sessionInvalidationCache.Get(key); found {
-			if invalidatedAt, ok := val.(int64); ok {
+			if invalidatedAt, ok := sessionInvalidationTime(val); ok {
 				// Sessions for this subject created at or before invalidation are invalid
 				invalidationTime := time.Unix(invalidatedAt, 0)
 				if !invalidationTime.Before(sessionCreatedAtSec) {
@@ -448,6 +494,25 @@ func (t *TraefikOidc) buildSessionInvalidationKey(keyType, value string) string
 	return fmt.Sprintf("session_invalidation:%s:%s", keyType, value)
 }
 
+// sessionCreatedAtForInvalidation returns the session creation time to use
+// for the backchannel/front-channel logout invalidation check. It prefers
+// the ID token's iat claim; when iat is absent, it falls back to the
+// session's own created_at (recorded at login) rather than time.Now().
+// Using time.Now() here meant a session whose ID token lacks iat was
+// always treated as created "now" (after any logout), so invalidation
+// never matched and IdP-initiated logout silently had no effect (R98).
+func (t *TraefikOidc) sessionCreatedAtForInvalidation(idToken string, session *SessionData) time.Time {
+	if jwt, err := parseJWT(idToken); err == nil {
+		if iat, ok := jwt.Claims["iat"].(float64); ok {
+			return time.Unix(int64(iat), 0)
+		}
+	}
+	if ca := session.getCreatedAtUnsafe(); ca > 0 {
+		return time.Unix(ca, 0)
+	}
+	return time.Time{} // zero: treated as invalidated -> safe re-auth
+}
+
 // extractSessionInfo extracts sid and sub from an ID token for session tracking
 func (t *TraefikOidc) extractSessionInfo(idToken string) (sid, sub string, createdAt time.Time) {
 	if idToken == "" {

metadata_cache.go

@@ -147,11 +147,13 @@ func (mc *MetadataCache) GetProviderMetadata(ctx context.Context, providerURL st
 	}
 
 	// Require the core endpoints. An incomplete discovery document (missing
-	// authorization_endpoint / token_endpoint) would otherwise be accepted,
-	// cached, and adopted as the working auth/token URL, failing at runtime
-	// (wrong authorize redirect, token-exchange failure) instead of at startup.
-	if metadata.AuthURL == "" || metadata.TokenURL == "" {
-		return nil, fmt.Errorf("discovery document missing required endpoints (authorization_endpoint or token_endpoint)")
+	// authorization_endpoint / token_endpoint / jwks_uri) would otherwise be
+	// accepted, cached, and adopted as the working auth/token/JWKS URL, failing
+	// at runtime (wrong authorize redirect, token-exchange failure, or signature
+	// verification failure — jwksURL has no non-discovery source) instead of at
+	// startup.
+	if metadata.AuthURL == "" || metadata.TokenURL == "" || metadata.JWKSURL == "" {
+		return nil, fmt.Errorf("discovery document missing required endpoints (authorization_endpoint, token_endpoint or jwks_uri)")
 	}
 
 	// Pin the advertised issuer to the configured provider host. The issuer is

middleware.go

@@ -4,9 +4,12 @@
 package traefikoidc
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
+	"net"
 	"net/http"
+	"regexp"
 	"runtime/debug"
 	"strings"
 	"sync/atomic"
@@ -15,6 +18,45 @@ import (
 	"github.com/lukaszraczylo/traefikoidc/internal/utils"
 )
 
+// trackingWriter wraps an http.ResponseWriter so the deferred panic handler
+// can tell whether a response was already committed. WriteHeader is
+// idempotent so calling it again after commit is a no-op, but a later
+// Write appends to the committed body - so writing "Internal Server
+// Error" after a handler has already produced a valid 200 (or a 302
+// redirect) corrupts the response. Flush/Hijack are forwarded so
+// downstream SSE and WebSocket handlers keep working through the wrapper.
+type trackingWriter struct {
+	http.ResponseWriter
+	wroteHeader bool
+}
+
+func (w *trackingWriter) WriteHeader(code int) {
+	w.wroteHeader = true
+	w.ResponseWriter.WriteHeader(code)
+}
+
+func (w *trackingWriter) Write(b []byte) (int, error) {
+	w.wroteHeader = true
+	return w.ResponseWriter.Write(b)
+}
+
+func (w *trackingWriter) Flush() {
+	w.wroteHeader = true
+	if f, ok := w.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
+}
+
+func (w *trackingWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	w.wroteHeader = true
+	if h, ok := w.ResponseWriter.(http.Hijacker); ok {
+		return h.Hijack()
+	}
+	return nil, nil, http.ErrNotSupported
+}
+
+func (w *trackingWriter) Unwrap() http.ResponseWriter { return w.ResponseWriter }
+
 // bypassReason describes why a request is being forwarded without OIDC auth.
 // It is only used for logging and to decide whether extra side-effects
 // (propagating the user header from an existing session) should run.
@@ -22,6 +64,7 @@ const (
 	bypassReasonExcluded  = "excluded-url"
 	bypassReasonSSE       = "sse"
 	bypassReasonWebSocket = "websocket"
+	bypassReasonOptions   = "options"
 )
 
 // isWebSocketUpgrade reports whether req is a WebSocket upgrade handshake
@@ -54,6 +97,14 @@ func (t *TraefikOidc) shouldBypassAuth(req *http.Request) (bool, string) {
 	if t.determineExcludedURL(req.URL.Path) {
 		return true, bypassReasonExcluded
 	}
+	// CORS preflights carry no session cookie and must reach the backend so
+	// it can answer with Access-Control-Allow-*. Otherwise the 401 here
+	// (with no ACAO headers, since the security applier only runs on the
+	// authenticated path) makes the browser block the cross-origin
+	// request entirely and the real request never proceeds (R124).
+	if req.Method == http.MethodOptions {
+		return true, bypassReasonOptions
+	}
 	if strings.Contains(req.Header.Get("Accept"), "text/event-stream") {
 		return true, bypassReasonSSE
 	}
@@ -80,6 +131,29 @@ func (t *TraefikOidc) shouldBypassAuth(req *http.Request) (bool, string) {
 // The second return value (0 when forwarding) is the HTTP status to send
 // when the request is rejected, letting the caller distinguish a 401
 // (unauthenticated) from a 403 (authenticated but not permitted).
+// identityHeaders are the headers this middleware owns upstream. It
+// unconditionally strips any inbound values with these names before
+// forwarding — both on authenticated and bypassed requests — so forged
+// values (e.g. X-Forwarded-User: admin on a public path) can never
+// reach the backend and be trusted for downstream authorization.
+var identityHeaders = []string{
+	"X-Forwarded-User",
+	"X-User-Groups",
+	"X-User-Roles",
+	"X-Auth-Request-User",
+	"X-Auth-Request-Redirect",
+	"X-Auth-Request-Token",
+}
+
+// stripIdentityHeaders removes any inbound identity headers from req. The
+// middleware re-injects its own authoritative values afterwards where
+// appropriate. See identityHeaders.
+func stripIdentityHeaders(req *http.Request) {
+	for _, h := range identityHeaders {
+		req.Header.Del(h)
+	}
+}
+
 func (t *TraefikOidc) applyBypassUserHeaders(req *http.Request, reason string) (bool, int) {
 	if t.sessionManager == nil {
 		return false, http.StatusUnauthorized
@@ -115,14 +189,25 @@ func (t *TraefikOidc) applyBypassUserHeaders(req *http.Request, reason string) (
 	// Enforce the allowedRolesAndGroups gate, mirroring forwardAuthorized:
 	// an authenticated user without any permitted role/group must not reach
 	// the SSE/WebSocket backend just by using the streaming bypass. Claims
-	// come from the session's ID token, same source the normal path uses.
+	// come from the session's ID token by preference, falling back to the
+	// access token when there is no ID token — the same source selection the
+	// main authorization path (processAuthorizedRequest) uses. Without the
+	// fallback, opaque-ID-token providers (groups only in the access token)
+	// were granted on normal requests but 403'd on the streaming bypass
+	// (R118).
 	if len(t.allowedRolesAndGroups) > 0 {
-		idClaims, claimsErr := session.GetIDTokenClaims(t.extractClaimsFunc)
-		if claimsErr != nil || idClaims == nil {
+		var groupClaims map[string]interface{}
+		var claimsErr error
+		if idToken := session.GetIDToken(); idToken != "" {
+			groupClaims, claimsErr = session.GetIDTokenClaims(t.extractClaimsFunc)
+		} else if accessToken := session.GetAccessToken(); accessToken != "" {
+			groupClaims, claimsErr = t.extractClaimsFunc(accessToken)
+		}
+		if claimsErr != nil || groupClaims == nil {
 			t.logger.Debugf("%s bypass: cannot read claims for role check (err=%v): %s", reason, claimsErr, userIdentifier)
 			return false, http.StatusForbidden
 		}
-		groups, roles, extErr := t.extractGroupsAndRolesFromClaims(idClaims)
+		groups, roles, extErr := t.extractGroupsAndRolesFromClaims(groupClaims)
 		if extErr != nil {
 			t.logger.Debugf("%s bypass: role extraction failed for %s: %v", reason, userIdentifier, extErr)
 			return false, http.StatusForbidden
@@ -140,6 +225,17 @@ func (t *TraefikOidc) applyBypassUserHeaders(req *http.Request, reason string) (
 		}
 	}
 
+	// This middleware fully owns the identity headers it injects upstream, even
+	// on the SSE/WebSocket bypass path. Unconditionally remove inbound values
+	// for the same names first: a client can forge X-User-Groups /
+	// X-Auth-Request-User etc. on a bypassed request, and since this path
+	// only sets X-Forwarded-User / X-Auth-Request-User (never groups/roles),
+	// forged group/role headers would otherwise survive to the backend,
+	// which commonly trusts them for downstream authorization. Must precede
+	// the sanitize gate so even the drop-on-unsafe early return has already
+	// cleared forged values (R100).
+	stripIdentityHeaders(req)
+
 	// Sanitize the claim-derived identifier before it is injected as a
 	// header, matching forwardAuthorized (which uses safeIdentifier). The
 	// value originates from an IdP-controlled claim and can contain CRLF
@@ -172,20 +268,82 @@ func (t *TraefikOidc) applyBypassUserHeaders(req *http.Request, reason string) (
 // Parameters:
 //   - rw: The HTTP response writer.
 //   - req: The incoming HTTP request.
+//
+// shouldSkipGraceRefresh reports whether a proactive refresh can be skipped for
+// this request. The token forwarded downstream (forwardAuthorized) is the
+// ACCESS token, and needsRefresh (validateStandardTokensRS -> validateTokenExpiryRS)
+// is derived from the ACCESS token's expiry whenever it is a verifiable JWT.
+// Basing the skip decision on the (possibly longer-lived) ID token's exp would
+// forward a stale access token whenever the ID token is still fresh. Base it on
+// the access token's expiry, falling back to the ID token only when the access
+// token is opaque and unparseable (worst case: refresh when a skip might have
+// been possible — the safe direction).
+func (t *TraefikOidc) shouldSkipGraceRefresh(session *SessionData) bool {
+	return skipRefreshForTokens(session.GetAccessToken(), session.GetIDToken(), t.refreshGracePeriod)
+}
+
+// skipRefreshForTokens reports whether a proactive refresh can be skipped given
+// the session's access and ID tokens.
+func skipRefreshForTokens(accessToken, idToken string, grace time.Duration) bool {
+	graceToken := accessToken
+	graceJWT, graceErr := parseJWT(graceToken)
+	if graceErr != nil || graceJWT == nil {
+		graceToken = idToken
+		graceJWT, graceErr = parseJWT(graceToken)
+	}
+	if graceJWT == nil || graceErr != nil {
+		return false
+	}
+	expClaim, ok := graceJWT.Claims["exp"].(float64)
+	if !ok {
+		return false
+	}
+	expTimeObj := time.Unix(int64(expClaim), 0)
+	return !expTimeObj.Before(time.Now().Add(grace))
+}
+
 func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	// Track whether a response has been committed so the panic handler can
+	// avoid appending an error body to an already-emitted valid response.
+	tw := &trackingWriter{ResponseWriter: rw}
+	rw = tw
 	// Recover from any panic in the handler chain (session decode, token
 	// validation, header injection, authorize-url build) so a bug answers a
 	// single clean 500 (and logs a stack) instead of escaping to net/http,
-	// which closes/truncates the connection. WriteHeader is idempotent, so
-	// this is safe even if a handler already wrote headers; Write appends.
+	// which closes/truncates the connection. If the response was already
+	// committed by a handler (200 + body or a redirect), WriteHeader is an
+	// idempotent no-op and appending the body would corrupt a valid
+	// response, so only write when nothing has been sent yet.
 	defer func() {
 		if r := recover(); r != nil {
 			t.logger.Errorf("OIDC handler panic recovered: %v\n%s", r, debug.Stack())
-			rw.WriteHeader(http.StatusInternalServerError)
-			_, _ = rw.Write([]byte("Internal Server Error"))
+			if !tw.wroteHeader {
+				// A panic-induced 500 must not be cached (consistent with
+				// every other auth-failure response, R101/R172).
+				rw.Header().Set("Cache-Control", "no-store")
+				rw.WriteHeader(http.StatusInternalServerError)
+				_, _ = rw.Write([]byte("Internal Server Error"))
+			}
 		}
 	}()
 
+	// Apply security headers to EVERY response this middleware authors
+	// (redirects, error pages, bypass forwards, and authenticated
+	// forwards), not just the forwardAuthorized tail. Previously they only
+	// reached successfully-authenticated forwarding, so the initial
+	// 302-to-IdP, /health, /metrics, error pages and SSE/WS responses
+	// carried no Strict-Transport-Security / framing / MIME sniffing
+	// protections (R132).
+	if t.securityHeadersApplier != nil {
+		t.securityHeadersApplier(rw, req)
+	} else {
+		// Fallback to basic security headers
+		rw.Header().Set("X-Frame-Options", "DENY")
+		rw.Header().Set("X-Content-Type-Options", "nosniff")
+		rw.Header().Set("X-XSS-Protection", "1; mode=block")
+		rw.Header().Set("Referrer-Policy", "strict-origin-when-cross-origin")
+	}
+
 	// Log request entry for debugging routing issues
 	t.logger.Debugf("Incoming request: %s %s", req.Method, req.URL.Path)
 
@@ -241,12 +399,20 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		// public endpoint logs via downstream services that don't expect it.
 		// Excluded URLs are explicitly public; bearer is an artifact of the
 		// API auth flow that doesn't belong on them.
-		if t.enableBearerAuth {
+		// Also honor stripAuthorizationHeader (default true) so a raw
+		// client-supplied Authorization header is not forwarded verbatim on
+		// the SSE/WebSocket/excluded bypass — the same leak R144 closed for
+		// the normal path was left open on the streaming bypass (R151).
+		if t.enableBearerAuth || t.stripAuthorizationHeader {
 			req.Header.Del("Authorization")
 		}
 		switch reason {
 		case bypassReasonExcluded:
 			// Operator-declared excluded URLs forward unconditionally.
+			// These are public paths; still strip any client-forged
+			// identity headers so X-Forwarded-User / X-User-Groups etc.
+			// on a public endpoint can't be trusted downstream (R102).
+			stripIdentityHeaders(req)
 			t.next.ServeHTTP(rw, req)
 		case bypassReasonSSE, bypassReasonWebSocket:
 			// Skip the OIDC redirect dance (clients can't follow it
@@ -263,6 +429,11 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 				return
 			}
 			t.next.ServeHTTP(rw, req)
+		case bypassReasonOptions:
+			// CORS preflight: forward unconditionally (no session needed)
+			// so the backend can answer with CORS headers.
+			stripIdentityHeaders(req)
+			t.next.ServeHTTP(rw, req)
 		default:
 			t.next.ServeHTTP(rw, req)
 		}
@@ -351,14 +522,31 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		cleanReq := req.Clone(req.Context())
 		session, _ = t.sessionManager.GetSession(cleanReq) // Safe to ignore: error already logged, proceeding with new session
 		if session != nil {
-			defer session.returnToPoolSafely()
 			if clearErr := session.Clear(cleanReq, rw); clearErr != nil {
 				t.logger.Errorf("Error clearing potentially corrupted session: %v", clearErr)
 			}
-		} else {
-			t.logger.Error("Critical session error: Failed to get even a new session.")
-			t.sendErrorResponse(rw, req, "Critical session error", http.StatusInternalServerError)
-			return
+			// Clear() returns the session to the object pool, so discard the
+			// pointer — reusing it would be a use-after-return, since a
+			// concurrent GetSession may already own the pooled object
+			// (cross-request session bleed / data race). Obtain a fresh
+			// owned session in the shared block below. (R108)
+			session = nil
+		}
+		if session == nil {
+			// Session cookie is expired (past sessionMaxAge): a fresh
+			// GetSession still re-reads the same expired cookie and returns
+			// nil, so obtain a clean session and let the shared block below
+			// re-initiate authentication rather than returning 500 —
+			// otherwise every request past the session max age is a 500
+			// with no way to recover (R97).
+			session = t.sessionManager.newSession(cleanReq)
+			if session == nil {
+				t.logger.Error("Critical session error: Failed to get even a new session.")
+				t.sendErrorResponse(rw, req, "Critical session error", http.StatusInternalServerError)
+				return
+			}
+			defer session.returnToPoolSafely()
+			t.logger.Infof("Session expired or unreadable; re-initiating authentication")
 		}
 		// Sub-resource requests (script/image/fetch/serviceWorker) must not
 		// trigger an OIDC redirect from this path either: they would overwrite
@@ -398,6 +586,19 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	t.logger.Debugf("Checking callback URL match: request_path=%q, configured_callback=%q", req.URL.Path, t.redirURLPath)
 	if req.URL.Path == t.redirURLPath {
 		t.logger.Debugf("Callback URL matched, processing OIDC callback (redirect_url=%s)", redirectURL)
+		// The authorization-code response is delivered to the redirect
+		// endpoint via HTTP GET (RFC 6749 §3.1.2): handleCallback reads
+		// code/state/error only from the query string (form_post is not
+		// supported - a POST would see an empty query and fail with "No
+		// authorization code" anyway). Reject other methods with 405 so a
+		// HEAD/non-GET probe doesn't consume the one-time state and code
+		// and emit a 302 (R181).
+		if req.Method != http.MethodGet {
+			t.logger.Debugf("Callback requested with method %s (want GET); returning 405", req.Method)
+			rw.Header().Set("Cache-Control", "no-store")
+			rw.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
 		t.handleCallback(rw, req, redirectURL)
 		return
 	}
@@ -466,25 +667,17 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	}
 
 	if shouldAttemptRefresh {
-		idToken := session.GetIDToken()
-		if idToken != "" {
-			jwt, err := parseJWT(idToken)
-			if err == nil {
-				claims := jwt.Claims
-				if expClaim, ok := claims["exp"].(float64); ok {
-					expTime := int64(expClaim)
-					expTimeObj := time.Unix(expTime, 0)
-					refreshThreshold := time.Now().Add(t.refreshGracePeriod)
-
-					if !expTimeObj.Before(refreshThreshold) {
-						t.logger.Debug("Token is valid and outside grace period, skipping refresh")
-						t.processAuthorizedRequest(rw, req, session, redirectURL)
-						return
-					}
-				} else {
-					t.logger.Debug("Could not extract 'exp' claim for grace period check, proceeding with refresh")
-				}
-			}
+		// Only skip the proactive refresh when the session is genuinely
+		// authenticated. skipRefreshForTokens only parseJWT's the access
+		// token and reads the raw exp claim — it does not verify the
+		// signature or identity, so gating on the authenticated flag keeps
+		// an unauthenticated session (or one that failed verification for a
+		// non-expiry reason) from being bare-forwarded past the allowlist
+		// gate (R142).
+		if authenticated && t.shouldSkipGraceRefresh(session) {
+			t.logger.Debug("Token is valid and outside grace period, skipping refresh")
+			t.processAuthorizedRequest(rw, req, session, redirectURL)
+			return
 		}
 
 		if needsRefresh && authenticated {
@@ -574,7 +767,8 @@ func (t *TraefikOidc) processAuthorizedRequestRS(rw http.ResponseWriter, req *ht
 	idToken := rs.idToken
 	if t.enableBackchannelLogout || t.enableFrontchannelLogout {
 		if idToken != "" {
-			sid, sub, createdAt := t.extractSessionInfo(idToken)
+			sid, sub, _ := t.extractSessionInfo(idToken)
+			createdAt := t.sessionCreatedAtForInvalidation(idToken, session)
 			if t.isSessionInvalidated(sid, sub, createdAt) {
 				t.logger.Infof("Session for user %s has been invalidated via IdP-initiated logout", userIdentifier)
 				if err := session.Clear(req, rw); err != nil {
@@ -666,7 +860,8 @@ func (t *TraefikOidc) processAuthorizedRequest(rw http.ResponseWriter, req *http
 	if t.enableBackchannelLogout || t.enableFrontchannelLogout {
 		idToken := session.GetIDToken()
 		if idToken != "" {
-			sid, sub, createdAt := t.extractSessionInfo(idToken)
+			sid, sub, _ := t.extractSessionInfo(idToken)
+			createdAt := t.sessionCreatedAtForInvalidation(idToken, session)
 			if t.isSessionInvalidated(sid, sub, createdAt) {
 				t.logger.Infof("Session for user %s has been invalidated via IdP-initiated logout", userIdentifier)
 				// Clear the session and redirect to login
@@ -788,6 +983,18 @@ const headerTemplateMaxLen = 8192
 // optional claim the provider does not emit does not leak "<no value>".
 const noValueSentinel = "<no value>"
 
+// noValueTokenRe matches "<no value>" only as a whole token (bounded by
+// non-alphanumerics or string end), so a legitimate claim value that
+// happens to contain the substring survives the strip instead of being
+// corrupted (R103).
+var noValueTokenRe = regexp.MustCompile(`(^|[^0-9A-Za-z])` + regexp.QuoteMeta(noValueSentinel) + `([^0-9A-Za-z]|$)`)
+
+// stripNoValueSentinels removes text/template's missing-key placeholder
+// only when it appears as a whole token.
+func stripNoValueSentinels(s string) string {
+	return noValueTokenRe.ReplaceAllString(s, "${1}${2}")
+}
+
 // headerClaimMaxLen returns the maximum accepted length for a claim-derived
 // header value (principal identifier, group, role). Reuses the operator-
 // configured identifier cap (default 256) so a single setting governs both
@@ -820,7 +1027,46 @@ func (t *TraefikOidc) sanitizeHeaderClaimList(values []string, headerName string
 	return safe
 }
 
+// joinBoundedClaimHeader joins sanitized claim values with commas, bounding
+// the TOTAL length to headerTemplateMaxLen. A provider can return an
+// unbounded number of groups/roles; joining them all into a single header
+// would let an oversized value reach a downstream proxy that rejects or
+// truncates over-long headers (431), even though each value already passed
+// the per-value cap. Accumulates as many leading values as fit, so a
+// well-formed list is unaffected; an empty result means nothing fit and the
+// caller should drop the header (fail-closed).
+func joinBoundedClaimHeader(values []string) string {
+	if len(values) == 0 {
+		return ""
+	}
+	var b strings.Builder
+	for _, v := range values {
+		sep := 0
+		if b.Len() > 0 {
+			sep = 1 // leading comma
+		}
+		if b.Len()+sep+len(v) > headerTemplateMaxLen {
+			break
+		}
+		if sep > 0 {
+			b.WriteByte(',')
+		}
+		b.WriteString(v)
+	}
+	return b.String()
+}
+
 func (t *TraefikOidc) forwardAuthorized(rw http.ResponseWriter, req *http.Request, p *principal) {
+	// This middleware fully owns the identity headers it injects upstream.
+	// Unconditionally remove any inbound values with the same names first:
+	// a request could carry a forged X-User-Groups / X-Auth-Request-User
+	// etc. that, if the middleware computes no value for one of them
+	// (e.g. an authenticated user with no groups, an absent ID token, a
+	// a header-template skip), would otherwise survive through to the
+	// backend and be trusted for downstream authorization. Clearing here —
+	// before any conditional Set — makes the values we emit authoritative.
+	stripIdentityHeaders(req)
+
 	var (
 		groups, roles []string
 		extractErr    error
@@ -844,11 +1090,24 @@ func (t *TraefikOidc) forwardAuthorized(rw http.ResponseWriter, req *http.Reques
 			// header injection and an embedded comma would inject extra
 			// entries into the comma-joined header. Fail closed: drop any
 			// value that does not pass.
-			if safeGroups := t.sanitizeHeaderClaimList(groups, "X-User-Groups"); len(safeGroups) > 0 {
-				req.Header.Set("X-User-Groups", strings.Join(safeGroups, ","))
-			}
-			if safeRoles := t.sanitizeHeaderClaimList(roles, "X-User-Roles"); len(safeRoles) > 0 {
-				req.Header.Set("X-User-Roles", strings.Join(safeRoles, ","))
+			// X-User-Groups / X-User-Roles are the largest variably-sized
+			// forward headers; gate them behind minimalHeaders like the
+			// X-Auth-Request-* family so group-heavy users don't still trip
+			// HTTP 431 on the backend (the failure minimalHeaders exists to
+			// prevent, #64). Identity (X-Forwarded-User) stays
+			// unconditional; the allowedRolesAndGroups gate below still
+			// evaluates groups regardless of emission.
+			if !t.minimalHeaders {
+				if safeGroups := t.sanitizeHeaderClaimList(groups, "X-User-Groups"); len(safeGroups) > 0 {
+					if gh := joinBoundedClaimHeader(safeGroups); gh != "" {
+						req.Header.Set("X-User-Groups", gh)
+					}
+				}
+				if safeRoles := t.sanitizeHeaderClaimList(roles, "X-User-Roles"); len(safeRoles) > 0 {
+					if rh := joinBoundedClaimHeader(safeRoles); rh != "" {
+						req.Header.Set("X-User-Roles", rh)
+					}
+				}
 			}
 		}
 	}
@@ -902,17 +1161,29 @@ func (t *TraefikOidc) forwardAuthorized(rw http.ResponseWriter, req *http.Reques
 			t.logger.Debugf("Dropping X-Auth-Request-User header: identifier failed claim sanitization")
 		}
 		if p.IDToken != "" {
-			req.Header.Set("X-Auth-Request-Token", p.IDToken)
+			// Bound the raw ID token to the same header budget as rendered
+			// template values so a large token can't push this (and every
+			// other header on the request) past nginx/traefik 431 limits.
+			idTokenHeader := p.IDToken
+			if len(idTokenHeader) > headerTemplateMaxLen {
+				idTokenHeader = idTokenHeader[:headerTemplateMaxLen]
+			}
+			req.Header.Set("X-Auth-Request-Token", idTokenHeader)
 		}
 	}
 
-	// Bearer source: strip the raw inbound Authorization header to keep the
-	// token out of downstream service logs (off-by-config for operators who
-	// chain services that each re-verify the bearer). Stripped here, before
-	// header-template application, so an operator-supplied Authorization
-	// template (e.g. "Authorization: Bearer {{.AccessToken}}") can re-supply
-	// the downstream value rather than being immediately deleted.
-	if p.Source == sourceBearer && t.stripAuthorizationHeader {
+	// Strip the raw inbound Authorization header for BOTH auth paths when
+	// configured. The bearer path already stripped it; the cookie/session
+	// path forwarded a client-supplied Authorization verbatim, letting a
+	// session user present an arbitrary (and possibly more privileged)
+	// bearer that a downstream verifier might trust over X-Forwarded-User,
+	// or leaking a raw token into downstream logs. Kept out of downstream
+	// logs and make X-Forwarded-User / X-Auth-Request-Token the
+	// authoritative identity signal. Stripped here, before header-template
+	// application, so an operator-supplied Authorization template (e.g.
+	// "Authorization: Bearer {{.AccessToken}}") can re-supply the
+	// downstream value rather than being immediately deleted.
+	if t.stripAuthorizationHeader {
 		req.Header.Del("Authorization")
 	}
 
@@ -942,7 +1213,7 @@ func (t *TraefikOidc) forwardAuthorized(rw http.ResponseWriter, req *http.Reques
 			// optional claim the provider did not emit (e.g. email) does not
 			// leak "<no value>" into the downstream header.
 			if strings.Contains(headerValue, noValueSentinel) {
-				headerValue = strings.ReplaceAll(headerValue, noValueSentinel, "")
+				headerValue = stripNoValueSentinels(headerValue)
 			}
 			// Skip an empty render: Setting "" would clobber an identity
 			// header (X-Forwarded-User / X-Auth-Request-*) already injected
@@ -970,17 +1241,6 @@ func (t *TraefikOidc) forwardAuthorized(rw http.ResponseWriter, req *http.Reques
 		}
 	}
 
-	// Apply security headers if configured
-	if t.securityHeadersApplier != nil {
-		t.securityHeadersApplier(rw, req)
-	} else {
-		// Fallback to basic security headers
-		rw.Header().Set("X-Frame-Options", "DENY")
-		rw.Header().Set("X-Content-Type-Options", "nosniff")
-		rw.Header().Set("X-XSS-Protection", "1; mode=block")
-		rw.Header().Set("Referrer-Policy", "strict-origin-when-cross-origin")
-	}
-
 	// Strip OIDC session cookies before forwarding to the backend to prevent
 	// HTTP 431 "Request Header Fields Too Large" errors (GitHub issue #122).
 	if t.stripAuthCookies && t.sessionManager != nil {

profiling.go

@@ -35,6 +35,10 @@ type MemorySnapshot struct {
 	HeapProfile      []byte
 	GoroutineProfile []byte
 	RuntimeStats     runtime.MemStats
+	// Goroutines is the goroutine count (runtime.NumGoroutine()) captured at
+	// snapshot time, so leak analysis can diff a baseline against a later
+	// snapshot instead of sampling "now" twice (R118).
+	Goroutines int
 }
 
 // LeakAnalysis contains the results of memory leak detection and analysis.
@@ -118,10 +122,22 @@ func NewProfilingManager(logger *Logger) *ProfilingManager {
 // TakeSnapshot captures a comprehensive snapshot of current memory statistics.
 // Includes runtime stats, heap profile, goroutine profile, and custom metrics.
 func (pm *ProfilingManager) TakeSnapshot() (*MemorySnapshot, error) {
+	pm.mu.RLock()
+	defer pm.mu.RUnlock()
+	return pm.takeSnapshot()
+}
+
+// takeSnapshot implements TakeSnapshot assuming the caller already holds the
+// lock (either RLock for the public API, or the write Lock during
+// Start/StopProfiling). Calling the public TakeSnapshot from Start/Stop
+// while holding pm.mu.Lock() would self-deadlock (an RWMutex is not
+// recursively re-entrant on the write side) — R118.
+func (pm *ProfilingManager) takeSnapshot() (*MemorySnapshot, error) { // nolint:unparam // error return kept for the exported TakeSnapshot contract
 	var buf bytes.Buffer
 	snapshot := &MemorySnapshot{
 		Timestamp:     time.Now(),
 		CustomMetrics: make(map[string]interface{}),
+		Goroutines:    runtime.NumGoroutine(),
 	}
 
 	runtime.ReadMemStats(&snapshot.RuntimeStats)
@@ -146,13 +162,11 @@ func (pm *ProfilingManager) TakeSnapshot() (*MemorySnapshot, error) {
 		}
 	}
 
-	pm.mu.RLock()
 	for name, profiler := range pm.profilers {
 		if customStats := profiler.GetCurrentStats(); customStats != nil {
 			snapshot.CustomMetrics[name] = customStats
 		}
 	}
-	pm.mu.RUnlock()
 
 	return snapshot, nil
 }
@@ -170,7 +184,7 @@ func (pm *ProfilingManager) StartProfiling(config ProfilingConfig) error {
 	pm.isProfiling = true
 	pm.startTime = time.Now()
 
-	baseline, err := pm.TakeSnapshot()
+	baseline, err := pm.takeSnapshot() // lock already held -> use unlocked variant
 	if err != nil {
 		pm.isProfiling = false
 		return fmt.Errorf("failed to take baseline snapshot: %w", err)
@@ -190,7 +204,7 @@ func (pm *ProfilingManager) StopProfiling() (*MemorySnapshot, error) {
 		return nil, fmt.Errorf("profiling not in progress")
 	}
 
-	finalSnapshot, err := pm.TakeSnapshot()
+	finalSnapshot, err := pm.takeSnapshot() // lock already held -> use unlocked variant
 	if err != nil {
 		pm.logger.Errorf("Failed to take final snapshot: %v", err)
 	}
@@ -225,8 +239,12 @@ func (pm *ProfilingManager) AnalyzeLeaks(baseline, current *MemorySnapshot) *Lea
 	memoryIncrease := current.RuntimeStats.Alloc - baseline.RuntimeStats.Alloc
 	analysis.MemoryIncrease = memoryIncrease
 
+	// Diff against the goroutine count captured when the baseline snapshot
+	// was taken, not a live double-sample at analysis time. Sampling "now"
+	// for both values made the increase always 0 and the goroutine-leak
+	// branch permanently dead (R118).
+	baselineGoroutines := baseline.Goroutines
 	currentGoroutines := runtime.NumGoroutine()
-	baselineGoroutines := runtime.NumGoroutine()
 	goroutineIncrease := currentGoroutines - baselineGoroutines
 	analysis.GoroutineIncrease = goroutineIncrease
 

refresh_coordinator.go

@@ -183,7 +183,7 @@ func NewRefreshCoordinator(config RefreshCoordinatorConfig, logger *Logger) *Ref
 	rc := &RefreshCoordinator{
 		// inFlightRefreshes and sessionRefreshAttempts are both sync.Map;
 		// their zero values are ready to use.
-		config:        config,
+		config:   config,
 		metrics:  &RefreshMetrics{},
 		logger:   logger,
 		stopChan: make(chan struct{}),
@@ -225,10 +225,22 @@ func (rc *RefreshCoordinator) CoordinateRefresh(
 
 	// CRITICAL FIX: Atomically check for existing operation OR create new one
 	// This prevents the race where multiple goroutines check, find nothing, then all create
+	//
+	// R154: increment the WaitGroup BEFORE getOrCreateOperation registers
+	// the operation. Previously the Add(1) happened only after the op was
+	// registered and published as new, so a concurrent Shutdown
+	// (close(stopChan); wg.Wait) could observe the registered op, see a
+	// zero wg count, and return before this goroutine's Add landed — the
+	// just-started refresh then ran past Shutdown unreaped. Done() is
+	// balanced once per path: by the spawned goroutine, or immediately
+	// on the join/reject paths (which spawn nothing).
+	rc.wg.Add(1)
+
 	operation, isNew, err := rc.getOrCreateOperation(ctx, sessionID, tokenHash, refreshToken)
 
 	if err != nil {
 		// Operation creation was rejected (rate limit, memory pressure, concurrent limit)
+		rc.wg.Done() // no goroutine launched
 		return nil, err
 	}
 
@@ -236,7 +248,6 @@ func (rc *RefreshCoordinator) CoordinateRefresh(
 		// We created a new operation, so we need to execute it. Track the
 		// goroutine so Shutdown waits for in-flight refreshes to finish (they
 		// are aborted promptly via rc.ctx when stopChan closes).
-		rc.wg.Add(1)
 		go func() {
 			defer rc.wg.Done()
 			rc.executeRefreshAsync(operation, sessionID, tokenHash, refreshFunc) //nolint:gosec // long-lived background refresh intentionally uses a background context
@@ -244,6 +255,7 @@ func (rc *RefreshCoordinator) CoordinateRefresh(
 	} else {
 		// Joined existing operation - this is a deduplicated request
 		atomic.AddInt64(&rc.metrics.deduplicatedRequests, 1)
+		rc.wg.Done() // joined an existing op; no goroutine tracked here
 	}
 
 	// Wait for the operation to complete
@@ -665,15 +677,20 @@ func refreshCoordinatorSessionID(token string) string {
 const refreshCoordinatorWaitTimeout = 35 * time.Second
 
 // isUnderMemoryPressure checks if the system is under memory pressure by
-// consulting the global memory monitor. Returns true when pressure reaches
-// High or Critical, at which point we refuse new refresh operations to
-// avoid aggravating an already-stressed heap.
+// consulting the global memory monitor. Returns true when the current heap
+// exceeds the coordinator's OWN configured MemoryPressureThresholdMB, at
+// which point we refuse new refresh operations to avoid aggravating an
+// already-stressed heap.
 func (rc *RefreshCoordinator) isUnderMemoryPressure() bool {
 	monitor := GetGlobalMemoryMonitor()
 	if monitor == nil {
 		return false
 	}
-	return monitor.GetMemoryPressure() >= MemoryPressureHigh
+	stats := monitor.GetCurrentStats()
+	if stats == nil || rc.config.MemoryPressureThresholdMB == 0 {
+		return false
+	}
+	return stats.HeapAllocBytes > rc.config.MemoryPressureThresholdMB*1024*1024
 }
 
 // cleanupRoutine periodically cleans up stale tracking entries

requeststate.go

@@ -32,12 +32,12 @@ type requestState struct {
 	// (Save, Clear, etc.) still have access.
 	session *SessionData
 
-	authenticated     bool
-	accessToken       string
-	idToken           string
-	refreshToken      string
-	userIdentifier    string
-	createdAtUnixSec  int64
+	authenticated    bool
+	accessToken      string
+	idToken          string
+	refreshToken     string
+	userIdentifier   string
+	createdAtUnixSec int64
 
 	// Output: scheme/host/redirect path determined at top of ServeHTTP.
 	scheme      string

scope_filter.go

@@ -38,7 +38,10 @@ func (sf *ScopeFilter) FilterSupportedScopes(requestedScopes, supportedScopes []
 	// If no supported scopes declared, return all requested (backward compatibility)
 	if len(supportedScopes) == 0 {
 		sf.logger.Debugf("ScopeFilter: Provider %s has no scopes_supported in discovery doc, using all requested scopes", providerURL)
-		return requestedScopes
+		// Return a copy so the caller can append without aliasing the
+		// slice it passed in (which would let the two views of the same
+		// backing array cross-contaminate each other).
+		return append([]string(nil), requestedScopes...)
 	}
 
 	// Build lookup map for efficient checking

session.go

@@ -140,12 +140,14 @@ type combinedSessionPayload struct {
 	X  map[string]interface{} `json:"x,omitempty"`
 	A  string                 `json:"a,omitempty"`
 	R  string                 `json:"r,omitempty"`
+	Ri int64                  `json:"ri,omitempty"` // refresh-token issued_at (unix), preserved so maxRefreshTokenAge survives combined round-trip
 	I  string                 `json:"i,omitempty"`
 	Ui string                 `json:"ui,omitempty"`
 	Cs string                 `json:"cs,omitempty"`
 	N  string                 `json:"n,omitempty"`
 	Cv string                 `json:"cv,omitempty"`
 	Ip string                 `json:"ip,omitempty"`
+	Ru string                 `json:"ru,omitempty"` // redirect_uri used at initiate; reused at callback so a per-request rebuild can't drift (R136)
 	Ca int64                  `json:"ca,omitempty"`
 	Rc int                    `json:"rc,omitempty"`
 	Au bool                   `json:"au,omitempty"`
@@ -163,6 +165,7 @@ var knownSessionKeys = map[string]bool{
 	"nonce":           true,
 	"code_verifier":   true,
 	"incoming_path":   true,
+	"redirect_url":    true,
 	"created_at":      true,
 	"redirect_count":  true,
 }
@@ -381,16 +384,6 @@ func decompressTokenInternal(compressed string) string {
 
 	limitedReader := io.LimitReader(gz, 500*1024)
 
-	if cap(readerBuf) >= 512*1024 {
-		readerBuf = readerBuf[:cap(readerBuf)]
-		n, err := limitedReader.Read(readerBuf)
-		if err != nil && err != io.EOF {
-			return compressed
-		}
-		decompressed := readerBuf[:n]
-		return string(decompressed)
-	}
-
 	decompressed, err := io.ReadAll(limitedReader)
 	if err != nil {
 		return compressed
@@ -912,6 +905,14 @@ func (sm *SessionManager) EnhanceSessionSecurity(options *sessions.Options, r *h
 		sm.logger.Debugf("Using configured cookie domain: %s", sm.cookieDomain)
 	} else if options.Domain == "" && r != nil {
 		host := r.Host
+		// Strip the port before the subdomain-bounding check below; a ported
+		// r.Host (e.g. app.example.com:8080) would otherwise fail
+		// HasSuffix(host, "."+fh) and wrongly fall back to the strict
+		// parent X-Forwarded-Host, scoping the token-bearing session cookie
+		// to every sibling subdomain.
+		if ci := strings.Index(host, ":"); ci != -1 {
+			host = host[:ci]
+		}
 
 		if forwardedHost := r.Header.Get("X-Forwarded-Host"); forwardedHost != "" {
 			// Only use the forwarded host when it is the serving host or a
@@ -1029,7 +1030,7 @@ func (sm *SessionManager) CleanupOldCookies(w http.ResponseWriter, r *http.Reque
 						Domain:   domain,
 						MaxAge:   -1,
 						HttpOnly: true,
-						Secure:   r.Header.Get("X-Forwarded-Proto") == "https" || r.TLS != nil || sm.forceHTTPS,
+						Secure:   strings.EqualFold(r.Header.Get("X-Forwarded-Proto"), "https") || r.TLS != nil || sm.forceHTTPS,
 						SameSite: http.SameSiteLaxMode,
 					}
 					http.SetCookie(w, deleteCookie)
@@ -1059,7 +1060,44 @@ func (sm *SessionManager) CleanupOldCookies(w http.ResponseWriter, r *http.Reque
 //
 // Returns:
 //   - The loaded SessionData instance.
-//   - An error if session loading or validation fails.
+//
+// newSession returns a clean, pooled session with no cookie state loaded. It
+// is used when the request's session cookie is expired: GetSession keeps
+// re-reading that same expired cookie and returns nil, so the caller needs a
+// fresh session to (re-)initiate authentication rather than erroring out.
+// Mirrors GetSession's pool/activeSessions accounting.
+func (sm *SessionManager) newSession(r *http.Request) *SessionData {
+	sessionData, _ := sm.sessionPool.Get().(*SessionData) // Safe to ignore: pool return is best-effort
+	if sessionData == nil {
+		return nil
+	}
+	sessionData.Reset() // clear any stale state from a previous pooled user
+	sessionData.request = r
+	sessionData.inUse.Store(true)
+	sessionData.dirty = false
+	atomic.AddInt64(&sm.poolHits, 1)
+	atomic.AddInt64(&sm.activeSessions, 1)
+
+	// GetSession normally populates the four legacy sub-sessions from the
+	// request; newSession runs where that read already failed (expired
+	// cookie), so initialize non-nil containers here. Downstream auth
+	// flow (SetCSRF/SetNonce/... then Save) writes through these.
+	if sessionData.mainSession == nil {
+		sessionData.mainSession, _ = sm.store.Get(r, sm.mainCookieName())
+	}
+	if sessionData.accessSession == nil {
+		sessionData.accessSession, _ = sm.store.Get(r, sm.accessTokenCookieName())
+	}
+	if sessionData.refreshSession == nil {
+		sessionData.refreshSession, _ = sm.store.Get(r, sm.refreshTokenCookieName())
+	}
+	if sessionData.idTokenSession == nil {
+		sessionData.idTokenSession, _ = sm.store.Get(r, sm.idTokenCookieName())
+	}
+	return sessionData
+}
+
+// - An error if session loading or validation fails.
 func (sm *SessionManager) GetSession(r *http.Request) (*SessionData, error) {
 	sessionData, _ := sm.sessionPool.Get().(*SessionData) // Safe to ignore: pool return is best-effort
 	atomic.AddInt64(&sm.poolHits, 1)
@@ -1230,6 +1268,7 @@ func (sm *SessionManager) loadFromCombinedCookies(r *http.Request, sessionData *
 	sessionData.mainSession.Values["nonce"] = payload.N
 	sessionData.mainSession.Values["code_verifier"] = payload.Cv
 	sessionData.mainSession.Values["incoming_path"] = payload.Ip
+	sessionData.mainSession.Values["redirect_url"] = payload.Ru
 	sessionData.mainSession.Values["created_at"] = payload.Ca
 	sessionData.mainSession.Values["redirect_count"] = payload.Rc
 
@@ -1243,6 +1282,9 @@ func (sm *SessionManager) loadFromCombinedCookies(r *http.Request, sessionData *
 
 	sessionData.refreshSession.Values["token"] = payload.R
 	sessionData.refreshSession.Values["compressed"] = false
+	if payload.Ri > 0 {
+		sessionData.refreshSession.Values["issued_at"] = payload.Ri
+	}
 
 	sessionData.idTokenSession.Values["token"] = payload.I
 	sessionData.idTokenSession.Values["compressed"] = false
@@ -1259,7 +1301,14 @@ func (sm *SessionManager) loadFromCombinedCookies(r *http.Request, sessionData *
 //   - chunks: The map (typically SessionData.accessTokenChunks or SessionData.refreshTokenChunks)
 //     to populate with the found session chunks.
 func (sm *SessionManager) getTokenChunkSessions(r *http.Request, baseName string, chunks map[int]*sessions.Session) {
-	for i := 0; ; i++ {
+	// Bound the scan at MaxChunks (50) so an oversized set of chunk
+	// cookies (attack or corruption) can't drive unbounded
+	// securecookie decrypts. Loading through index 50 still lets
+	// processChunkedToken's len(chunks) > MaxChunks check fire, so the
+	// overflow → error behavior is unchanged; indices beyond 50 would be
+	// rejected anyway (R183).
+	const maxChunkScan = 50
+	for i := 0; i <= maxChunkScan; i++ {
 		sessionName := fmt.Sprintf("%s_%d", baseName, i)
 		session, err := sm.store.Get(r, sessionName)
 		if err != nil || session.IsNew {
@@ -1305,6 +1354,12 @@ type SessionData struct {
 
 	dirty bool
 
+	// expireCookie is a one-shot flag set by Clear to force the cookies it
+	// writes to be expired (Max-Age: -1). Without it, Save rebuilds a
+	// positive MaxAge and logout leaves an empty session cookie alive for
+	// the full session lifetime instead of expiring it (R101).
+	expireCookie bool
+
 	inUse atomic.Bool
 
 	// cachedClaimsToken is the ID token string whose claims were last parsed and
@@ -1346,11 +1401,23 @@ func (sd *SessionData) MarkDirty() {
 // Returns:
 //   - An error if saving any of the session components fails.
 func (sd *SessionData) Save(r *http.Request, w http.ResponseWriter) error {
-	isSecure := r.Header.Get("X-Forwarded-Proto") == "https" || r.TLS != nil || sd.manager.forceHTTPS
+	// X-Forwarded-Proto value is compared case-insensitively: reverse proxies
+	// (nginx, Traefik) emit lowercase "https", but a client-controllable or
+	// non-canonical value like "HTTPS" must still yield a Secure cookie.
+	// Case-sensitive comparison here would silently downgrade the session
+	// cookie to transport-unsafe on such a header (R143).
+	isSecure := strings.EqualFold(r.Header.Get("X-Forwarded-Proto"), "https") || r.TLS != nil || sd.manager.forceHTTPS
 
 	options := sd.manager.getSessionOptions(isSecure)
 	options = sd.manager.EnhanceSessionSecurity(options, r)
 
+	if sd.expireCookie {
+		// Clear set this flag: the cookies written below must be expired,
+		// not re-issued with a fresh positive MaxAge.
+		options.MaxAge = -1
+		sd.expireCookie = false
+	}
+
 	// Use combined storage for new sessions
 	if sd.useCombinedStorage {
 		return sd.saveCombined(r, w, options)
@@ -1363,7 +1430,11 @@ func (sd *SessionData) Save(r *http.Request, w http.ResponseWriter) error {
 // saveCombined saves all session data in a single compressed, chunked cookie.
 // This reduces cookie count and total size through combined compression.
 func (sd *SessionData) saveCombined(r *http.Request, w http.ResponseWriter, options *sessions.Options) error {
-	// Build the combined payload
+	// Build the combined payload. All token/main fields are read under
+	// sessionMutex.RLock so a concurrent Set* (which writes under the
+	// write side) can't tear the payload mid-build (R132). The extra-map
+	// walk below already took the Read side; extend it to the field reads.
+	sd.sessionMutex.RLock()
 	payload := &combinedSessionPayload{
 		A:  sd.getAccessTokenUnsafe(),
 		R:  sd.getRefreshTokenUnsafe(),
@@ -1374,12 +1445,18 @@ func (sd *SessionData) saveCombined(r *http.Request, w http.ResponseWriter, opti
 		N:  sd.getNonceUnsafe(),
 		Cv: sd.getCodeVerifierUnsafe(),
 		Ip: sd.getIncomingPathUnsafe(),
+		Ru: sd.getRedirectURLUnsafe(),
 		Ca: sd.getCreatedAtUnsafe(),
 		Rc: sd.getRedirectCountUnsafe(),
 	}
+	// Persist the refresh token's issued_at so maxRefreshTokenAge keeps
+	// working after a combined save/load round-trip (it lives on
+	// refreshSession, which is otherwise dropped by combined storage).
+	if ra, ok := sd.refreshSession.Values["issued_at"].(int64); ok {
+		payload.Ri = ra
+	}
 
 	// Collect extra session values not handled by the standard fields
-	sd.sessionMutex.RLock()
 	if sd.mainSession != nil && len(sd.mainSession.Values) > 0 {
 		extra := make(map[string]interface{})
 		for key, val := range sd.mainSession.Values {
@@ -1404,7 +1481,11 @@ func (sd *SessionData) saveCombined(r *http.Request, w http.ResponseWriter, opti
 	compressed, err := compressCombinedPayload(payload)
 	if err != nil {
 		sd.manager.logger.Errorf("Failed to compress combined payload: %v", err)
-		// Fall back to legacy storage on compression failure
+		// Fall back to legacy storage on compression failure. Expire any
+		// pre-existing combined chunk cookies first, or GetSession
+		// (combined-first) would keep serving the stale combined payload
+		// and shadow the freshly written legacy tokens (R163).
+		sd.expireOldCombinedChunks(r, w, options, 0)
 		return sd.saveLegacy(r, w, options)
 	}
 
@@ -1413,8 +1494,15 @@ func (sd *SessionData) saveCombined(r *http.Request, w http.ResponseWriter, opti
 	// Split into chunks
 	chunks := splitCombinedIntoChunks(compressed, maxCookieSize)
 	if len(chunks) > maxCombinedChunks {
-		sd.manager.logger.Errorf("Combined session requires %d chunks, exceeds max %d", len(chunks), maxCombinedChunks)
-		return fmt.Errorf("session data too large: requires %d chunks, max is %d", len(chunks), maxCombinedChunks)
+		sd.manager.logger.Errorf("Combined session requires %d chunks, exceeds max %d; falling back to legacy storage", len(chunks), maxCombinedChunks)
+		// The legacy path supports up to 50 token chunks (~100KB), so large
+		// tokens must not drop the session entirely — persist via the
+		// legacy (per-token chunk) format instead of erroring and forcing
+		// the user to re-authenticate (R97). Expire the old combined
+		// chunks first so GetSession's combined-first read serves the
+		// fresh legacy tokens rather than the stale combined payload (R163).
+		sd.expireOldCombinedChunks(r, w, options, 0)
+		return sd.saveLegacy(r, w, options)
 	}
 
 	sd.manager.logger.Debugf("Combined session split into %d chunks", len(chunks))
@@ -1573,20 +1661,24 @@ func (sd *SessionData) expireLegacyCookies(r *http.Request, w http.ResponseWrite
 	expireLegacyMain(sd.manager.refreshTokenCookieName())
 	expireLegacyMain(sd.manager.idTokenCookieName())
 
-	// Expire legacy chunk cookies (safe to clear values, they're separate from main sessions)
-	for i := 0; i < 50; i++ { // Max legacy chunks was 50
-		accessChunk := fmt.Sprintf("%s_%d", sd.manager.accessTokenCookieName(), i)
-		refreshChunk := fmt.Sprintf("%s_%d", sd.manager.refreshTokenCookieName(), i)
-		idChunk := fmt.Sprintf("%s_%d", sd.manager.idTokenCookieName(), i)
-
-		session, err := sd.manager.store.Get(r, accessChunk)
-		if err != nil || session.IsNew {
-			break // No more chunks
+	// Expire legacy chunk cookies (safe to clear values, they're separate from main sessions).
+	// Each token type is walked to its own limit so a small, un-chunked access token
+	// does not gate refresh/id chunk expiry (R133 P2-A): previously the shared
+	// access-driven loop broke all three series at the first absent access chunk,
+	// leaving stale refresh/id legacy chunk cookies behind after combined migration.
+	expireLegacyChunkSeries := func(baseName string) {
+		for i := 0; i < 50; i++ { // Max legacy chunks was 50
+			chunk := fmt.Sprintf("%s_%d", baseName, i)
+			session, err := sd.manager.store.Get(r, chunk)
+			if err != nil || session.IsNew {
+				break // No more chunks for this token type
+			}
+			expireLegacyChunk(chunk)
 		}
-		expireLegacyChunk(accessChunk)
-		expireLegacyChunk(refreshChunk)
-		expireLegacyChunk(idChunk)
 	}
+	expireLegacyChunkSeries(sd.manager.accessTokenCookieName())
+	expireLegacyChunkSeries(sd.manager.refreshTokenCookieName())
+	expireLegacyChunkSeries(sd.manager.idTokenCookieName())
 }
 
 // clearSessionValues removes all values from a session and optionally expires it.
@@ -1667,6 +1759,7 @@ func (sd *SessionData) Clear(r *http.Request, w http.ResponseWriter) error {
 			// Return a test error without trying to save problematic data
 			err = fmt.Errorf("test error triggered by X-Test-Error header")
 		} else {
+			sd.expireCookie = true
 			err = sd.Save(r, w)
 		}
 	}
@@ -1973,19 +2066,19 @@ func (sd *SessionData) SetAccessToken(token string) {
 		return
 	}
 
-	if sd.request != nil {
-		sd.expireAccessTokenChunksEnhanced(nil)
-	}
-
-	for k := range sd.accessTokenChunks {
-		delete(sd.accessTokenChunks, k)
-	}
+	// Defer clearing the PREVIOUS access token (its HTTP chunk cookies and the
+	// in-memory chunk map) until the new token's storage is fully validated.
+	// Clearing first, then aborting on a too-large new token (>100KB after
+	// compression, or >50 chunks) would leave the previous still-valid access
+	// token nowhere — GetAccessToken returns "" and the user is forced to
+	// re-authenticate (R122). We commit the clear only once we're replacing it.
 
 	if token == "" {
 		if sd.accessSession != nil {
 			sd.accessSession.Values["token"] = ""
 			sd.accessSession.Values["compressed"] = false
 		}
+		sd.clearAccessTokenChunks()
 		return
 	}
 
@@ -2014,6 +2107,7 @@ func (sd *SessionData) SetAccessToken(token string) {
 	}
 
 	if len(compressed) <= maxCookieSize {
+		sd.clearAccessTokenChunks()
 		if sd.accessSession != nil {
 			sd.accessSession.Values["token"] = compressed
 			sd.accessSession.Values["compressed"] = (compressed != token)
@@ -2024,10 +2118,12 @@ func (sd *SessionData) SetAccessToken(token string) {
 			}
 		}
 	} else {
-		if sd.accessSession != nil {
-			sd.accessSession.Values["token"] = ""
-			sd.accessSession.Values["compressed"] = (compressed != token)
-		}
+		// WARNING: do not clear the existing token (accessSession.Values
+		// ["token"] / accessTokenChunks) until the new token's chunks are
+		// validated below. Clearing first meant an abort on any chunk
+		// failure (too many chunks, reassembly mismatch) left NO token
+		// anywhere -> GetAccessToken returned "" -> forced re-auth (data
+		// loss of the previous still-valid access token).
 
 		chunks := splitIntoChunks(compressed, maxCookieSize)
 
@@ -2042,11 +2138,23 @@ func (sd *SessionData) SetAccessToken(token string) {
 		}
 
 		testReassembled := strings.Join(chunks, "")
+		// R188 cross-chunk integrity: bind all chunks to one another so a
+		// mix of authentic-but-different chunk sets is caught at assembly
+		// (see processChunkedToken). Stored on every chunk.
+		chunkIntegrity := fmt.Sprintf("%x", sha256.Sum256([]byte(testReassembled)))
 		if testReassembled != compressed {
 			sd.manager.logger.Debug("Access token chunk reassembly test failed")
 			return
 		}
 
+		// Validation passed: now it is safe to clear the existing token
+		// before storing the new chunked one.
+		sd.clearAccessTokenChunks()
+		if sd.accessSession != nil {
+			sd.accessSession.Values["token"] = ""
+			sd.accessSession.Values["compressed"] = (compressed != token)
+		}
+
 		for i, chunkData := range chunks {
 			sessionName := fmt.Sprintf("%s_%d", sd.manager.accessTokenCookieName(), i)
 
@@ -2080,6 +2188,7 @@ func (sd *SessionData) SetAccessToken(token string) {
 			session.Values["compressed"] = (compressed != token)
 			session.Values["chunk_created_at"] = time.Now().Unix()
 			session.Values["token_total"] = len(chunks)
+			session.Values["chunk_integrity"] = chunkIntegrity
 			sd.accessTokenChunks[i] = session
 		}
 
@@ -2087,6 +2196,20 @@ func (sd *SessionData) SetAccessToken(token string) {
 	}
 }
 
+// clearAccessTokenChunks expires the current access token's HTTP chunk cookies
+// (via expireAccessTokenChunksEnhanced) and clears the in-memory access
+// token chunk map. Callers invoke it only once they are committed to
+// replacing the token, so a failed (too-large) store leaves the previous
+// valid access token intact. Called with sd.sessionMutex already held.
+func (sd *SessionData) clearAccessTokenChunks() {
+	if sd.request != nil {
+		sd.expireAccessTokenChunksEnhanced(nil)
+	}
+	for k := range sd.accessTokenChunks {
+		delete(sd.accessTokenChunks, k)
+	}
+}
+
 // GetRefreshToken retrieves the user's refresh token from session storage.
 // It handles both single-cookie storage and chunked storage for large tokens,
 // with automatic decompression if the token was compressed.
@@ -2182,15 +2305,14 @@ func (sd *SessionData) SetRefreshToken(token string) {
 	}
 	sd.dirty = true
 
-	if sd.request != nil {
-		sd.expireRefreshTokenChunksEnhanced(nil)
-	}
-
-	for k := range sd.refreshTokenChunks {
-		delete(sd.refreshTokenChunks, k)
-	}
-
 	if token == "" {
+		// Explicit clear: the caller wants the previous token gone.
+		if sd.request != nil {
+			sd.expireRefreshTokenChunksEnhanced(nil)
+		}
+		for k := range sd.refreshTokenChunks {
+			delete(sd.refreshTokenChunks, k)
+		}
 		sd.refreshSession.Values["token"] = ""
 		sd.refreshSession.Values["compressed"] = false
 		return
@@ -2207,70 +2329,98 @@ func (sd *SessionData) SetRefreshToken(token string) {
 	}
 
 	if len(compressed) <= maxCookieSize {
+		// Single-cookie layout: nothing to validate, safe to swap.
+		if sd.request != nil {
+			sd.expireRefreshTokenChunksEnhanced(nil)
+		}
+		for k := range sd.refreshTokenChunks {
+			delete(sd.refreshTokenChunks, k)
+		}
 		sd.refreshSession.Values["token"] = compressed
 		sd.refreshSession.Values["compressed"] = (compressed != token)
 		sd.refreshSession.Values["issued_at"] = time.Now().Unix()
-	} else {
-		sd.refreshSession.Values["token"] = ""
-		sd.refreshSession.Values["compressed"] = (compressed != token)
-		sd.refreshSession.Values["issued_at"] = time.Now().Unix()
-
-		chunks := splitIntoChunks(compressed, maxCookieSize)
-
-		if len(chunks) == 0 {
-			sd.manager.logger.Errorf("CRITICAL: Failed to create chunks for refresh token")
-			return
-		}
-
-		if len(chunks) > 50 {
-			sd.manager.logger.Errorf("CRITICAL: Too many chunks (%d) for refresh token - possible corruption", len(chunks))
-			return
-		}
-
-		testReassembled := strings.Join(chunks, "")
-		if testReassembled != compressed {
-			sd.manager.logger.Errorf("CRITICAL: Refresh token chunk reassembly test failed")
-			return
-		}
-
-		for i, chunkData := range chunks {
-			sessionName := fmt.Sprintf("%s_%d", sd.manager.refreshTokenCookieName(), i)
-
-			if sd.request == nil {
-				sd.manager.logger.Errorf("CRITICAL: SetRefreshToken: sd.request is nil, cannot create chunk session %s", sessionName)
-				return
-			}
-
-			if chunkData == "" {
-				sd.manager.logger.Errorf("CRITICAL: Empty refresh token chunk data at index %d", i)
-				return
-			}
-
-			if len(chunkData) > maxCookieSize {
-				sd.manager.logger.Errorf("CRITICAL: Refresh token chunk %d size %d exceeds maxCookieSize %d", i, len(chunkData), maxCookieSize)
-				return
-			}
-
-			if !validateChunkSize(chunkData) {
-				sd.manager.logger.Errorf("CRITICAL: Refresh token chunk %d will exceed browser cookie limits after encoding (raw size: %d)", i, len(chunkData))
-				return
-			}
-
-			session, err := sd.manager.store.Get(sd.request, sessionName)
-			if err != nil {
-				sd.manager.logger.Errorf("CRITICAL: Failed to get refresh token chunk session %s: %v", sessionName, err)
-				return
-			}
-
-			session.Values["token_chunk"] = chunkData
-			session.Values["compressed"] = (compressed != token)
-			session.Values["chunk_created_at"] = time.Now().Unix()
-			session.Values["token_total"] = len(chunks)
-			sd.refreshTokenChunks[i] = session
-		}
-
-		sd.manager.logger.Debugf("SUCCESS: Stored refresh token in %d chunks", len(chunks))
+		return
 	}
+
+	// Chunked layout: validate and write every new chunk BEFORE touching the
+	// previous token, so an abort (request missing, store error, size check,
+	// reassembly) leaves the still-valid prior refresh token intact (R154;
+	// extends the R95 access-token fix to the refresh token).
+	chunks := splitIntoChunks(compressed, maxCookieSize)
+
+	if len(chunks) == 0 {
+		sd.manager.logger.Errorf("CRITICAL: Failed to create chunks for refresh token")
+		return
+	}
+
+	if len(chunks) > 50 {
+		sd.manager.logger.Errorf("CRITICAL: Too many chunks (%d) for refresh token - possible corruption", len(chunks))
+		return
+	}
+
+	testReassembled := strings.Join(chunks, "")
+	// R188 cross-chunk integrity: bind all chunks to one another so a mix
+	// of authentic-but-different chunk sets is caught at assembly (see
+	// processChunkedToken). Stored on every chunk.
+	chunkIntegrity := fmt.Sprintf("%x", sha256.Sum256([]byte(testReassembled)))
+	if testReassembled != compressed {
+		sd.manager.logger.Errorf("CRITICAL: Refresh token chunk reassembly test failed")
+		return
+	}
+
+	newChunks := make(map[int]*sessions.Session, len(chunks))
+	for i, chunkData := range chunks {
+		sessionName := fmt.Sprintf("%s_%d", sd.manager.refreshTokenCookieName(), i)
+
+		if sd.request == nil {
+			sd.manager.logger.Errorf("CRITICAL: SetRefreshToken: sd.request is nil, cannot create chunk session %s", sessionName)
+			return
+		}
+
+		if chunkData == "" {
+			sd.manager.logger.Errorf("CRITICAL: Empty refresh token chunk data at index %d", i)
+			return
+		}
+
+		if len(chunkData) > maxCookieSize {
+			sd.manager.logger.Errorf("CRITICAL: Refresh token chunk %d size %d exceeds maxCookieSize %d", i, len(chunkData), maxCookieSize)
+			return
+		}
+
+		if !validateChunkSize(chunkData) {
+			sd.manager.logger.Errorf("CRITICAL: Refresh token chunk %d will exceed browser cookie limits after encoding (raw size: %d)", i, len(chunkData))
+			return
+		}
+
+		session, err := sd.manager.store.Get(sd.request, sessionName)
+		if err != nil {
+			sd.manager.logger.Errorf("CRITICAL: Failed to get refresh token chunk session %s: %v", sessionName, err)
+			return
+		}
+
+		session.Values["token_chunk"] = chunkData
+		session.Values["compressed"] = (compressed != token)
+		session.Values["chunk_created_at"] = time.Now().Unix()
+		session.Values["token_total"] = len(chunks)
+		session.Values["chunk_integrity"] = chunkIntegrity
+		newChunks[i] = session
+	}
+
+	// Every new chunk committed: now it is safe to discard the old token.
+	if sd.request != nil {
+		sd.expireRefreshTokenChunksEnhanced(nil)
+	}
+	for k := range sd.refreshTokenChunks {
+		delete(sd.refreshTokenChunks, k)
+	}
+	sd.refreshSession.Values["token"] = ""
+	sd.refreshSession.Values["compressed"] = (compressed != token)
+	sd.refreshSession.Values["issued_at"] = time.Now().Unix()
+	for i, s := range newChunks {
+		sd.refreshTokenChunks[i] = s
+	}
+
+	sd.manager.logger.Debugf("SUCCESS: Stored refresh token in %d chunks", len(chunks))
 }
 
 // GetRefreshTokenIssuedAt retrieves the timestamp when the refresh token was issued/stored.
@@ -2517,6 +2667,8 @@ func isCorruptionMarker(data string) bool {
 // Returns:
 //   - The CSRF token string, or an empty string if not set.
 func (sd *SessionData) GetCSRF() string {
+	sd.sessionMutex.RLock()
+	defer sd.sessionMutex.RUnlock()
 	csrf, _ := sd.mainSession.Values["csrf"].(string)
 	return csrf
 }
@@ -2526,6 +2678,8 @@ func (sd *SessionData) GetCSRF() string {
 // Parameters:
 //   - token: The CSRF token to store.
 func (sd *SessionData) SetCSRF(token string) {
+	sd.sessionMutex.Lock()
+	defer sd.sessionMutex.Unlock()
 	currentVal, _ := sd.mainSession.Values["csrf"].(string)
 	if currentVal != token {
 		sd.mainSession.Values["csrf"] = token
@@ -2539,6 +2693,8 @@ func (sd *SessionData) SetCSRF(token string) {
 // Returns:
 //   - The nonce string, or an empty string if not set.
 func (sd *SessionData) GetNonce() string {
+	sd.sessionMutex.RLock()
+	defer sd.sessionMutex.RUnlock()
 	nonce, _ := sd.mainSession.Values["nonce"].(string)
 	return nonce
 }
@@ -2548,6 +2704,8 @@ func (sd *SessionData) GetNonce() string {
 // Parameters:
 //   - nonce: The nonce string to store.
 func (sd *SessionData) SetNonce(nonce string) {
+	sd.sessionMutex.Lock()
+	defer sd.sessionMutex.Unlock()
 	currentVal, _ := sd.mainSession.Values["nonce"].(string)
 	if currentVal != nonce {
 		sd.mainSession.Values["nonce"] = nonce
@@ -2561,6 +2719,8 @@ func (sd *SessionData) SetNonce(nonce string) {
 // Returns:
 //   - The code verifier string, or an empty string if not set or PKCE is disabled.
 func (sd *SessionData) GetCodeVerifier() string {
+	sd.sessionMutex.RLock()
+	defer sd.sessionMutex.RUnlock()
 	codeVerifier, _ := sd.mainSession.Values["code_verifier"].(string)
 	return codeVerifier
 }
@@ -2571,6 +2731,8 @@ func (sd *SessionData) GetCodeVerifier() string {
 // Parameters:
 //   - codeVerifier: The PKCE code verifier string to store.
 func (sd *SessionData) SetCodeVerifier(codeVerifier string) {
+	sd.sessionMutex.Lock()
+	defer sd.sessionMutex.Unlock()
 	currentVal, _ := sd.mainSession.Values["code_verifier"].(string)
 	if currentVal != codeVerifier {
 		sd.mainSession.Values["code_verifier"] = codeVerifier
@@ -2612,6 +2774,8 @@ func (sd *SessionData) SetUserIdentifier(userIdentifier string) {
 // Returns:
 //   - The original request URI string, or an empty string if not set.
 func (sd *SessionData) GetIncomingPath() string {
+	sd.sessionMutex.RLock()
+	defer sd.sessionMutex.RUnlock()
 	path, _ := sd.mainSession.Values["incoming_path"].(string)
 	return path
 }
@@ -2622,6 +2786,8 @@ func (sd *SessionData) GetIncomingPath() string {
 // Parameters:
 //   - path: The original request URI string (e.g., "/protected/resource?id=123").
 func (sd *SessionData) SetIncomingPath(path string) {
+	sd.sessionMutex.Lock()
+	defer sd.sessionMutex.Unlock()
 	currentVal, _ := sd.mainSession.Values["incoming_path"].(string)
 	if currentVal != path {
 		sd.mainSession.Values["incoming_path"] = path
@@ -2629,6 +2795,35 @@ func (sd *SessionData) SetIncomingPath(path string) {
 	}
 }
 
+// GetRedirectURL retrieves the fully-qualified redirect_uri persisted when the
+// authentication flow was initiated. It is consumed at the callback (in place
+// of a per-request rebuild) so a drift in X-Forwarded-Host between the
+// initiate and callback requests cannot change the redirect_uri sent to the
+// provider (R136).
+func (sd *SessionData) GetRedirectURL() string {
+	sd.sessionMutex.RLock()
+	defer sd.sessionMutex.RUnlock()
+	ru, _ := sd.mainSession.Values["redirect_url"].(string)
+	return ru
+}
+
+// SetRedirectURL stores the redirect_uri used at initiate time (R136).
+func (sd *SessionData) SetRedirectURL(redirectURL string) {
+	sd.sessionMutex.Lock()
+	defer sd.sessionMutex.Unlock()
+	currentVal, _ := sd.mainSession.Values["redirect_url"].(string)
+	if currentVal != redirectURL {
+		sd.mainSession.Values["redirect_url"] = redirectURL
+		sd.dirty = true
+	}
+}
+
+// getRedirectURLUnsafe retrieves the redirect URL without acquiring locks.
+func (sd *SessionData) getRedirectURLUnsafe() string {
+	ru, _ := sd.mainSession.Values["redirect_url"].(string)
+	return ru
+}
+
 // GetIDToken retrieves the user's ID token from session storage.
 // The ID token contains user claims and is used for user identification
 // and authorization decisions. Handles compression and chunking automatically.
@@ -2804,14 +2999,6 @@ func (sd *SessionData) SetIDToken(token string) {
 	}
 	sd.dirty = true
 
-	if sd.request != nil {
-		sd.expireIDTokenChunksEnhanced(nil)
-	}
-
-	for k := range sd.idTokenChunks {
-		delete(sd.idTokenChunks, k)
-	}
-
 	if token == "" {
 		if sd.idTokenSession != nil {
 			sd.idTokenSession.Values["token"] = ""
@@ -2831,72 +3018,100 @@ func (sd *SessionData) SetIDToken(token string) {
 	}
 
 	if len(compressed) <= maxCookieSize {
+		// Single-cookie layout: nothing to validate, safe to swap.
+		if sd.request != nil {
+			sd.expireIDTokenChunksEnhanced(nil)
+		}
+		for k := range sd.idTokenChunks {
+			delete(sd.idTokenChunks, k)
+		}
 		if sd.idTokenSession != nil {
 			sd.idTokenSession.Values["token"] = compressed
 			sd.idTokenSession.Values["compressed"] = (compressed != token)
 		}
-	} else {
-		if sd.idTokenSession != nil {
-			sd.idTokenSession.Values["token"] = ""
-			sd.idTokenSession.Values["compressed"] = (compressed != token)
-		}
-
-		chunks := splitIntoChunks(compressed, maxCookieSize)
-
-		if len(chunks) == 0 {
-			sd.manager.logger.Errorf("CRITICAL: Failed to create chunks for ID token")
-			return
-		}
-
-		if len(chunks) > 50 {
-			sd.manager.logger.Errorf("CRITICAL: Too many chunks (%d) for ID token - possible corruption", len(chunks))
-			return
-		}
-
-		testReassembled := strings.Join(chunks, "")
-		if testReassembled != compressed {
-			sd.manager.logger.Errorf("CRITICAL: ID token chunk reassembly test failed")
-			return
-		}
-
-		for i, chunkData := range chunks {
-			sessionName := fmt.Sprintf("%s_%d", sd.manager.idTokenCookieName(), i)
-
-			if sd.request == nil {
-				sd.manager.logger.Errorf("CRITICAL: SetIDToken: sd.request is nil, cannot create chunk session %s", sessionName)
-				return
-			}
-
-			if chunkData == "" {
-				sd.manager.logger.Debug("Empty chunk data at index %d", i)
-				return
-			}
-
-			if len(chunkData) > maxCookieSize {
-				sd.manager.logger.Info("Chunk %d size %d exceeds maxCookieSize %d", i, len(chunkData), maxCookieSize)
-				return
-			}
-
-			if !validateChunkSize(chunkData) {
-				sd.manager.logger.Errorf("CRITICAL: ID token chunk %d will exceed browser cookie limits after encoding (raw size: %d)", i, len(chunkData))
-				return
-			}
-
-			session, err := sd.manager.store.Get(sd.request, sessionName)
-			if err != nil {
-				sd.manager.logger.Errorf("CRITICAL: Failed to get chunk session %s: %v", sessionName, err)
-				return
-			}
-
-			session.Values["token_chunk"] = chunkData
-			session.Values["compressed"] = (compressed != token)
-			session.Values["chunk_created_at"] = time.Now().Unix()
-			session.Values["token_total"] = len(chunks)
-			sd.idTokenChunks[i] = session
-		}
-
-		sd.manager.logger.Debugf("SUCCESS: Stored ID token in %d chunks", len(chunks))
+		return
 	}
+
+	// Chunked layout: validate and write every new chunk BEFORE touching
+	// the previous token, so an abort (request missing, store error, size
+	// check) leaves the still-valid prior ID token intact (R154; extends
+	// the R95 access-token fix to the ID token).
+	chunks := splitIntoChunks(compressed, maxCookieSize)
+
+	if len(chunks) == 0 {
+		sd.manager.logger.Errorf("CRITICAL: Failed to create chunks for ID token")
+		return
+	}
+
+	if len(chunks) > 50 {
+		sd.manager.logger.Errorf("CRITICAL: Too many chunks (%d) for ID token - possible corruption", len(chunks))
+		return
+	}
+
+	testReassembled := strings.Join(chunks, "")
+	// R188 cross-chunk integrity: bind all chunks to one another so a mix
+	// of authentic-but-different chunk sets is caught at assembly (see
+	// processChunkedToken). Stored on every chunk.
+	chunkIntegrity := fmt.Sprintf("%x", sha256.Sum256([]byte(testReassembled)))
+	if testReassembled != compressed {
+		sd.manager.logger.Errorf("CRITICAL: ID token chunk reassembly test failed")
+		return
+	}
+
+	newChunks := make(map[int]*sessions.Session, len(chunks))
+	for i, chunkData := range chunks {
+		sessionName := fmt.Sprintf("%s_%d", sd.manager.idTokenCookieName(), i)
+
+		if sd.request == nil {
+			sd.manager.logger.Errorf("CRITICAL: SetIDToken: sd.request is nil, cannot create chunk session %s", sessionName)
+			return
+		}
+
+		if chunkData == "" {
+			sd.manager.logger.Debug("Empty chunk data at index %d", i)
+			return
+		}
+
+		if len(chunkData) > maxCookieSize {
+			sd.manager.logger.Info("Chunk %d size %d exceeds maxCookieSize %d", i, len(chunkData), maxCookieSize)
+			return
+		}
+
+		if !validateChunkSize(chunkData) {
+			sd.manager.logger.Errorf("CRITICAL: ID token chunk %d will exceed browser cookie limits after encoding (raw size: %d)", i, len(chunkData))
+			return
+		}
+
+		session, err := sd.manager.store.Get(sd.request, sessionName)
+		if err != nil {
+			sd.manager.logger.Errorf("CRITICAL: Failed to get chunk session %s: %v", sessionName, err)
+			return
+		}
+
+		session.Values["token_chunk"] = chunkData
+		session.Values["compressed"] = (compressed != token)
+		session.Values["chunk_created_at"] = time.Now().Unix()
+		session.Values["token_total"] = len(chunks)
+		session.Values["chunk_integrity"] = chunkIntegrity
+		newChunks[i] = session
+	}
+
+	// Every new chunk committed: now it is safe to discard the old token.
+	if sd.request != nil {
+		sd.expireIDTokenChunksEnhanced(nil)
+	}
+	for k := range sd.idTokenChunks {
+		delete(sd.idTokenChunks, k)
+	}
+	if sd.idTokenSession != nil {
+		sd.idTokenSession.Values["token"] = ""
+		sd.idTokenSession.Values["compressed"] = (compressed != token)
+	}
+	for i, s := range newChunks {
+		sd.idTokenChunks[i] = s
+	}
+
+	sd.manager.logger.Debugf("SUCCESS: Stored ID token in %d chunks", len(chunks))
 }
 
 // GetRedirectCount returns the number of redirects in the current authentication flow.

session_chunk_manager.go

@@ -3,6 +3,7 @@ package traefikoidc
 import (
 	"bytes"
 	"context"
+	"crypto/sha256"
 	"encoding/base64"
 	"fmt"
 	"strings"
@@ -41,10 +42,14 @@ func ResetGlobalSessionCounters() {
 // Predefined configurations for each token type
 var (
 	AccessTokenConfig = TokenConfig{
-		Type:              "access",
-		MinLength:         5,
-		MaxLength:         100 * 1024,
-		MaxChunks:         25,
+		Type:      "access",
+		MinLength: 5,
+		MaxLength: 100 * 1024,
+		// Must be >= the write path's hard chunk cap (session.go Set*Token
+		// allows up to 50 chunks) so a token that was written can always be
+		// read back. A lower read limit silently made written tokens
+		// unreadable (data loss / forced re-auth) — see R95.
+		MaxChunks:         50,
 		MaxChunkSize:      maxCookieSize,
 		AllowOpaqueTokens: true,
 		RequireJWTFormat:  false,
@@ -54,7 +59,7 @@ var (
 		Type:              "refresh",
 		MinLength:         5,
 		MaxLength:         50 * 1024,
-		MaxChunks:         15,
+		MaxChunks:         50, // R95: match write-path cap (see AccessTokenConfig)
 		MaxChunkSize:      maxCookieSize,
 		AllowOpaqueTokens: true,
 		RequireJWTFormat:  false,
@@ -64,7 +69,7 @@ var (
 		Type:              "id",
 		MinLength:         5,
 		MaxLength:         75 * 1024,
-		MaxChunks:         20,
+		MaxChunks:         50, // R95: match write-path cap (see AccessTokenConfig)
 		MaxChunkSize:      maxCookieSize,
 		AllowOpaqueTokens: false,
 		RequireJWTFormat:  true,
@@ -292,9 +297,7 @@ func (cm *ChunkManager) validateToken(token string, config TokenConfig) TokenRet
 		return TokenRetrievalResult{Token: "", Error: sizeErr}
 	}
 
-	if chunkErr := cm.validateChunkingEfficiency(token, config); chunkErr != nil {
-		return TokenRetrievalResult{Token: "", Error: chunkErr}
-	}
+	cm.validateChunkingEfficiency(token, config)
 
 	if contentErr := cm.validateTokenContent(token, config); contentErr != nil {
 		return TokenRetrievalResult{Token: "", Error: contentErr}
@@ -365,12 +368,27 @@ func (cm *ChunkManager) processChunkedToken(chunks map[int]*sessions.Session, co
 	// cookie eviction, dropped Set-Cookie, attacker dropping a cookie) would
 	// reassemble a truncated prefix with no error and trust it as the token.
 	// The write path stores token_total on every chunk; check it on chunk 0.
-	if total, ok := chunks[0].Values["token_total"].(int); ok {
-		if len(chunks) != total {
-			err := fmt.Errorf("%s token chunk count mismatch: got %d, expected %d (possibly truncated)",
-				config.Type, len(chunks), total)
-			cm.logger.Errorf("Truncated %s token chunks: got %d, expected %d", config.Type, len(chunks), total)
-			return TokenRetrievalResult{Token: "", Error: err}
+	// Guard against a sparse set missing index 0 (the assembly loop below
+	// reports the missing chunk; don't nil-deref here) (R148).
+	if first, has0 := chunks[0]; has0 && first != nil {
+		if total, ok := first.Values["token_total"].(int); ok {
+			if len(chunks) > total {
+				// Stale higher-index chunks left behind when a token was
+				// rewritten with fewer chunks (Set*Token writes 0..n-1 but does
+				// not clear cookies above n). token_total is the authoritative
+				// count; drop the excess rather than failing — which forced a
+				// re-auth and discarded the still-valid new token (R129).
+				n := len(chunks)
+				for i := total; i < n; i++ {
+					delete(chunks, i)
+				}
+			}
+			if len(chunks) < total {
+				err := fmt.Errorf("%s token chunk count mismatch: got %d, expected %d (possibly truncated)",
+					config.Type, len(chunks), total)
+				cm.logger.Errorf("Truncated %s token chunks: got %d, expected %d", config.Type, len(chunks), total)
+				return TokenRetrievalResult{Token: "", Error: err}
+			}
 		}
 	}
 
@@ -423,6 +441,27 @@ func (cm *ChunkManager) processChunkedToken(chunks map[int]*sessions.Session, co
 
 	reassembledToken := strings.Join(tokenParts, "")
 
+	// Cross-chunk integrity: chunk 0 (and every chunk, on new writes)
+	// carries a SHA-256 of the assembled chunk string. Each chunk is
+	// already individually authenticated by its own securecookie MAC, so
+	// forgery is impossible; this binds the chunks to ONE another, so an
+	// authentic-but-mixed set (a stale chunk from an earlier session
+	// combined with chunks from the current one, when counts still match)
+	// is detected here instead of assembling a wrong token that would only
+	// surface as a downstream JWT-validation failure. Absent (old
+	// sessions written before this) → verification is skipped, keeping
+	// backward compatibility (R188).
+	if first, has0 := chunks[0]; has0 && first != nil {
+		if want, ok := first.Values["chunk_integrity"].(string); ok && want != "" {
+			got := fmt.Sprintf("%x", sha256.Sum256([]byte(reassembledToken)))
+			if got != want {
+				err := fmt.Errorf("%s token chunk integrity mismatch: chunks appear to belong to different sessions", config.Type)
+				cm.logger.Error("Token chunk integrity mismatch for %s: chunks belong to different sessions", config.Type)
+				return TokenRetrievalResult{Token: "", Error: err}
+			}
+		}
+	}
+
 	compressed, _ := chunks[0].Values["compressed"].(bool)
 
 	if compressed {
@@ -601,7 +640,7 @@ func (cm *ChunkManager) validateTokenSize(token string, config TokenConfig) erro
 	}
 
 	if config.AllowOpaqueTokens && !strings.Contains(token, ".") {
-		if tokenLen > 8*1024 {
+		if tokenLen > config.MaxLength {
 			err := fmt.Errorf("%s opaque token unusually large (%d bytes)", config.Type, tokenLen)
 			return err
 		}
@@ -610,34 +649,23 @@ func (cm *ChunkManager) validateTokenSize(token string, config TokenConfig) erro
 	return nil
 }
 
-// validateChunkingEfficiency ensures that chunking is used appropriately.
-// It calculates expected chunk counts and warns about potential inefficiencies
-// in token storage strategies.
-// Parameters:
-//   - token: The token to analyze for chunking efficiency.
-//   - config: Token configuration with chunking limits.
-//
-// Returns:
-//   - An error if chunking requirements would be violated, nil if acceptable.
-func (cm *ChunkManager) validateChunkingEfficiency(token string, config TokenConfig) error {
+// validateChunkingEfficiency warns about potential inefficiencies in token
+// storage strategies based on the token's length. It is advisory only: the
+// actual chunk budget is enforced at write time on the stored (compressed)
+// representation (session.go), and the read path size-bounds tokens via
+// validateTokenSize. It must NOT hard-reject on the read path, which sees
+// the *decompressed* token: a large access token legitimately stored
+// compressed (e.g. decompressing to > MaxChunks*MaxChunkSize bytes) would
+// otherwise be permanently rejected on every read, forcing re-auth while
+// the valid token sits in the browser (R104).
+func (cm *ChunkManager) validateChunkingEfficiency(token string, config TokenConfig) {
 	tokenLen := len(token)
 
-	if tokenLen <= config.MaxChunkSize && tokenLen <= maxCookieSize {
-	}
-
 	expectedChunks := (tokenLen + config.MaxChunkSize - 1) / config.MaxChunkSize
-	if expectedChunks > config.MaxChunks {
-		err := fmt.Errorf("%s token would require %d chunks (max: %d)",
-			config.Type, expectedChunks, config.MaxChunks)
-		return err
-	}
-
 	if expectedChunks > 10 && tokenLen < 50*1024 {
 		cm.logger.Info("%s token requires many chunks (%d) for size (%d bytes) - consider token optimization",
 			config.Type, expectedChunks, tokenLen)
 	}
-
-	return nil
 }
 
 // validateTokenContent performs comprehensive token content validation.

token_introspection.go

@@ -79,8 +79,16 @@ func (t *TraefikOidc) introspectToken(token string) (*IntrospectionResponse, err
 	req.Header.Set("Accept", "application/json")
 
 	// Authenticate using client credentials (per RFC 7662 Section 2.1)
-	// The introspection endpoint requires authentication
-	req.SetBasicAuth(t.clientID, t.clientSecret)
+	// The introspection endpoint requires authentication.
+	// Snapshot clientID/clientSecret under metadataMu: DCR rewrites them at
+	// runtime (R137).
+	clientID, clientSecret, _, _, _ := t.clientCredentials()
+	// RFC 7662 §2.1 authenticates the introspection call exactly like the
+	// token and revocation endpoints: form-urlencode client_id and
+	// client_secret individually before base64 (RFC 6749 §2.3.1), so the
+	// three outbound auth paths send identical wire credentials for secrets
+	// containing reserved characters (see setOAuthBasicAuth).
+	setOAuthBasicAuth(req, clientID, clientSecret)
 
 	// Send request with circuit breaker if available
 	var resp *http.Response
@@ -114,11 +122,19 @@ func (t *TraefikOidc) introspectToken(token string) (*IntrospectionResponse, err
 		}
 	}()
 
-	// Check HTTP status
+	// Check HTTP status. Return a typed *HTTPError so callers can
+	// distinguish a definite client-side rejection (4xx: the presented
+	// token is unknown/revoked -> treat like active=false) from a
+	// transient provider failure (5xx / other), instead of substring-
+	// matching the message and misclassifying a revoked token as a
+	// transient error that falls through to ID-token-only auth (R156).
 	if resp.StatusCode != http.StatusOK {
 		limitReader := io.LimitReader(resp.Body, 1024*10)
 		body, _ := io.ReadAll(limitReader) // Safe to ignore: reading error body for diagnostics
-		return nil, fmt.Errorf("introspection endpoint returned status %d: %s", resp.StatusCode, string(body))
+		return nil, &HTTPError{
+			StatusCode: resp.StatusCode,
+			Message:    fmt.Sprintf("introspection endpoint returned status %d: %s", resp.StatusCode, string(body)),
+		}
 	}
 
 	// Parse response per RFC 7662 Section 2.2
@@ -127,8 +143,14 @@ func (t *TraefikOidc) introspectToken(token string) (*IntrospectionResponse, err
 		return nil, fmt.Errorf("failed to decode introspection response: %w", err)
 	}
 
-	// Cache the result
-	if t.introspectionCache != nil {
+	// Cache the result. Only positive (active) results are cached so a
+	// revoked token's negative entry cannot poison the cache for its full TTL
+	// Cache the result. Only positive (active) results are cached so a
+	// revoked token's negative entry cannot poison the cache for its full TTL
+	// and keep rejecting a re-issued token with the same string (R104).
+	// Inactive results are re-introspected on each request, letting a
+	// re-issued valid token pass immediately.
+	if t.introspectionCache != nil && introspectionResp.Active {
 		// Cache for a short duration or until token expiry (whichever is shorter)
 		cacheDuration := 5 * time.Minute
 		// When introspection is REQUIRED, operators expect near-real-time
@@ -160,6 +182,9 @@ func (t *TraefikOidc) introspectToken(token string) (*IntrospectionResponse, err
 // Returns:
 //   - error: Validation error if token is invalid, nil if valid
 func (t *TraefikOidc) validateOpaqueToken(token string) error {
+	// Snapshot clientID/audience under metadataMu: DCR rewrites them at
+	// runtime (R137).
+	clientID, _, _, audience, _ := t.clientCredentials()
 	// Check if opaque tokens are allowed
 	if !t.allowOpaqueTokens {
 		return fmt.Errorf("opaque tokens are not enabled (set allowOpaqueTokens to true)")
@@ -190,6 +215,19 @@ func (t *TraefikOidc) validateOpaqueToken(token string) error {
 		return fmt.Errorf("token is not active (revoked or expired)")
 	}
 
+	// An opaque token has no JWT header to classify it, so token_type is
+	// the only discriminator between an access token and a refresh token.
+	// An opaque refresh token introspected (or otherwise) as
+	// active=true, token_type=refresh_token must not be honored as a
+	// bearer access token (R149). RFC 7662's token_type is the RFC 6749
+	// token type, whose value for an access token is "Bearer" (RFC 6750)
+	// — accept both spellings providers use (R156). Per RFC 7662
+	// token_type may be omitted by compliant providers, so only reject on
+	// a definite non-access match.
+	if resp.TokenType != "" && resp.TokenType != "access_token" && resp.TokenType != "Bearer" {
+		return fmt.Errorf("token type %q is not a bearer access token", resp.TokenType)
+	}
+
 	// Validate expiration if present
 	if resp.Exp > 0 {
 		expTime := time.Unix(resp.Exp, 0)
@@ -212,12 +250,12 @@ func (t *TraefikOidc) validateOpaqueToken(token string) error {
 	// whose audience cannot be confirmed must not be accepted, otherwise a
 	// token minted for a different audience would pass. aud may be a single
 	// string or an array of strings (RFC 7662); verifyAudience handles both.
-	if t.audience != "" && t.audience != t.clientID {
+	if audience != "" && audience != clientID {
 		if resp.Aud == nil {
-			return fmt.Errorf("invalid audience: expected %s, introspection response has no audience", t.audience)
+			return fmt.Errorf("invalid audience: expected %s, introspection response has no audience", audience)
 		}
-		if err := verifyAudience(resp.Aud, t.audience); err != nil {
-			return fmt.Errorf("invalid audience: expected %s: %w", t.audience, err)
+		if err := verifyAudience(resp.Aud, audience); err != nil {
+			return fmt.Errorf("invalid audience: expected %s: %w", audience, err)
 		}
 	}
 

token_manager.go

@@ -7,6 +7,8 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -16,6 +18,12 @@ import (
 	"time"
 )
 
+// ErrRateLimitExceeded is returned by verifyTokenWithOpts when the shared
+// per-instance token-origin rate limiter is exhausted. Callers (e.g.
+// handleCallback) surface it as HTTP 429 + Retry-After rather than a
+// generic 500, so burst-driven throttling is not reported as a server error.
+var ErrRateLimitExceeded = errors.New("request rate limit exceeded")
+
 // VerifyToken verifies the validity of an ID token or access token.
 // It performs comprehensive validation including format checks, blacklist verification,
 // signature validation using JWKs, and standard claims validation. It also caches
@@ -32,6 +40,17 @@ func (t *TraefikOidc) VerifyToken(token string) error {
 	return t.verifyTokenWithOpts(token, verifyOpts{})
 }
 
+// clientCredentials returns a consistent snapshot of the client credential
+// fields under metadataMu. DCR (performDynamicClientRegistration, main.go)
+// can rewrite clientID/clientSecret/audience at runtime under metadataMu.Lock,
+// so every request-path reader must snapshot these fields under RLock rather
+// than read them directly (which would be a data race) (R137).
+func (t *TraefikOidc) clientCredentials() (clientID, clientSecret, clientAuthMethod, audience string, clientAssertion *ClientAssertionSigner) {
+	t.metadataMu.RLock()
+	defer t.metadataMu.RUnlock()
+	return t.clientID, t.clientSecret, t.clientAuthMethod, t.audience, t.clientAssertion
+}
+
 // verifyOpts are internal-only knobs for verifyTokenWithOpts. Kept unexported
 // because they expose subtle replay-protection semantics that are dangerous
 // to misuse.
@@ -77,6 +96,19 @@ func (t *TraefikOidc) verifyTokenWithOpts(token string, opts verifyOpts) error {
 	// dozens of times per second by validateStandardTokens.
 	if t.tokenCache != nil {
 		if claims, exists := t.tokenCache.Get(token); exists && len(claims) > 0 {
+			// A cached hit normally short-circuits the parse, but it must
+			// still reject a token whose JTI has been blacklisted: a
+			// rotated token that shares this cached string's JTI (IdP JTI
+			// reuse) but was revoked under a different raw value would
+			// otherwise keep returning "valid" until the cache TTL, while
+			// every cold presentation of it is rejected (R148).
+			if t.tokenBlacklist != nil && !t.disableReplayDetection {
+				if jti, ok := claims["jti"].(string); ok && jti != "" {
+					if b, exists := t.tokenBlacklist.Get(jti); exists && b != nil {
+						return fmt.Errorf("token replay detected (jti: %s) in cache", jti)
+					}
+				}
+			}
 			return nil
 		}
 	}
@@ -87,8 +119,10 @@ func (t *TraefikOidc) verifyTokenWithOpts(token string, opts verifyOpts) error {
 	}
 
 	tokenType := "UNKNOWN"
+	clientID := ""
+	clientID, _, _, _, _ = t.clientCredentials()
 	if aud, ok := parsedJWT.Claims["aud"]; ok {
-		if audStr, ok := aud.(string); ok && audStr == t.clientID {
+		if audStr, ok := aud.(string); ok && audStr == clientID {
 			tokenType = "ID_TOKEN"
 		}
 	}
@@ -105,18 +139,16 @@ func (t *TraefikOidc) verifyTokenWithOpts(token string, opts verifyOpts) error {
 	if jti, ok := parsedJWT.Claims["jti"].(string); ok && jti != "" {
 		// Skip JTI blacklist check if replay detection is disabled
 		if !t.disableReplayDetection {
-			if !strings.HasPrefix(token, "eyJhbGciOiJSUzI1NiIsImtpZCI6InRlc3Qta2V5LWlkIiwidHlwIjoiSldUIn0") {
-				if t.tokenBlacklist != nil {
-					if blacklisted, exists := t.tokenBlacklist.Get(jti); exists && blacklisted != nil {
-						return fmt.Errorf("token replay detected (jti: %s) in cache", jti)
-					}
+			if t.tokenBlacklist != nil {
+				if blacklisted, exists := t.tokenBlacklist.Get(jti); exists && blacklisted != nil {
+					return fmt.Errorf("token replay detected (jti: %s) in cache", jti)
 				}
 			}
 		}
 	}
 
 	if !t.limiter.Allow() {
-		return fmt.Errorf("rate limit exceeded")
+		return fmt.Errorf("%w", ErrRateLimitExceeded)
 	}
 
 	jwt := parsedJWT
@@ -142,7 +174,10 @@ func (t *TraefikOidc) verifyTokenWithOpts(token string, opts verifyOpts) error {
 			expTime := time.Unix(int64(expClaim), 0)
 			tokenDuration := time.Until(expTime)
 			if tokenDuration > 0 && tokenDuration < defaultBlacklistDuration {
-				expiry = expTime
+				// Extend by ClockSkewToleranceFuture so the replay entry
+				// covers the full acceptance window (exp + skew), closing
+				// the post-exp replay window (mirrors jwt.go, R179).
+				expiry = expTime.Add(ClockSkewToleranceFuture)
 			}
 			// else: keep default expiry for expired tokens or tokens >24h
 		}
@@ -162,13 +197,21 @@ func (t *TraefikOidc) verifyTokenWithOpts(token string, opts verifyOpts) error {
 		initReplayCache()
 		duration := time.Until(expiry)
 		if duration > 0 {
-			if shardedReplayCache != nil {
-				shardedReplayCache.Set(jti, true, duration)
+			// Guard the singleton read with replayCacheMu because
+			// cleanupReplayCache (jwt.go) can nil shardedReplayCache under
+			// the write lock. Mirror the locked read in jwt.go
+			// SetIfAbsent so the pointer deref below cannot race a nil-out.
+			replayCacheMu.RLock()
+			sc := shardedReplayCache
+			if sc != nil {
+				sc.Set(replayCacheKey(t.issuerURL, jti), true, duration)
+				replayCacheMu.RUnlock()
 			} else {
+				replayCacheMu.RUnlock()
 				// Fall back to legacy cache (should rarely happen)
 				replayCacheMu.Lock()
 				if replayCache != nil {
-					replayCache.Set(jti, true, duration)
+					replayCache.Set(replayCacheKey(t.issuerURL, jti), true, duration)
 				}
 				replayCacheMu.Unlock()
 			}
@@ -195,6 +238,21 @@ func (t *TraefikOidc) verifyToken(token string) error {
 //   - token: The verified token string to cache.
 //   - claims: The map of claims extracted from the verified token.
 func (t *TraefikOidc) cacheVerifiedToken(token string, claims map[string]interface{}) {
+	// Defense-in-depth (F1/R133): a concurrent RevokeToken may have
+	// blacklisted this token (raw or jti) after we passed the top-of-
+	// verify blacklist check but before we cache. Do not re-populate
+	// the verified-cache with a revoked token.
+	if t.tokenBlacklist != nil {
+		if b, ok := t.tokenBlacklist.Get(token); ok && b != nil {
+			return
+		}
+		if jti, okv := claims["jti"].(string); okv && jti != "" {
+			if b, ok := t.tokenBlacklist.Get(jti); ok && b != nil {
+				return
+			}
+		}
+	}
+
 	expClaim, ok := claims["exp"].(float64)
 	if !ok {
 		t.safeLogError("Failed to cache token: invalid 'exp' claim type")
@@ -204,7 +262,14 @@ func (t *TraefikOidc) cacheVerifiedToken(token string, claims map[string]interfa
 	expirationTime := time.Unix(int64(expClaim), 0)
 	now := time.Now()
 	duration := expirationTime.Sub(now)
-	t.tokenCache.Set(token, claims, duration)
+	// Do not cache an already-expired token under a negative TTL. Via the
+	// ClockSkewToleranceFuture leeway an expired-then-verified token can
+	// reach here; a negative TTL entry would sit in the cache as dead
+	// weight (only swept by the periodic cleanup) and its ExpiresAt
+	// would already be past, so every hit would re-verify anyway (R153).
+	if duration > 0 {
+		t.tokenCache.Set(token, claims, duration)
+	}
 }
 
 // detectTokenType efficiently detects whether a token is an ID token or access token.
@@ -226,6 +291,9 @@ func (t *TraefikOidc) detectTokenType(jwt *JWT, token string) bool {
 	sum := sha256.Sum256([]byte(token))
 	cacheKey := hex.EncodeToString(sum[:])
 
+	// Snapshot clientID under metadataMu: DCR rewrites it at runtime (R137).
+	clientID, _, _, _, _ := t.clientCredentials()
+
 	// Check cache first
 	if t.tokenTypeCache != nil {
 		if cachedType, found := t.tokenTypeCache.Get(cacheKey); found {
@@ -306,16 +374,20 @@ func (t *TraefikOidc) detectTokenType(jwt *JWT, token string) bool {
 	// 5. Check if aud == clientID only (ID token pattern)
 	if aud, ok := jwt.Claims["aud"]; ok {
 		// Check string audience
-		if audStr, ok := aud.(string); ok && audStr == t.clientID {
+		if audStr, ok := aud.(string); ok && audStr == clientID {
 			isIDToken = true
 		} else if audArr, ok := aud.([]interface{}); ok {
-			// Check array audience - only treat as ID token if client_id is sole audience
-			if len(audArr) == 1 {
-				for _, v := range audArr {
-					if str, ok := v.(string); ok && str == t.clientID {
-						isIDToken = true
-						break
-					}
+			// Check array audience - treat as ID token if client_id is
+			// present anywhere in the array. OIDC ID tokens legitimately
+			// carry multiple aud entries (e.g. [clientID, API-resource])
+			// in multi-audience setups; insisting on client_id being the
+			// SOLE audience misclassified such ID tokens as access tokens
+			// and then validated them against the broader 'audience'
+			// config instead of clientID, rejecting valid logins.
+			for _, v := range audArr {
+				if str, ok := v.(string); ok && str == clientID {
+					isIDToken = true
+					break
 				}
 			}
 		}
@@ -375,20 +447,32 @@ func (t *TraefikOidc) VerifyJWTSignatureAndClaims(jwt *JWT, token string) error
 	}
 
 	if err := verifySignatureWithKey(token, pubKey, alg); err != nil {
-		if !t.suppressDiagnosticLogs {
-			// Microsoft Graph access tokens carry a `nonce` JWT header and are
-			// signed in a proprietary form Microsoft documents as unverifiable
-			// by client applications. They reach this path only when the
-			// per-provider classifier (validateAzureTokens) didn't catch them,
-			// so log at debug to keep the error stream actionable while still
-			// surfacing the cause for diagnostics.
-			if _, isMSProprietary := jwt.Header["nonce"]; isMSProprietary {
-				t.safeLogDebugf("DIAGNOSTIC: Signature verification failed for kid=%s, alg=%s (Microsoft proprietary nonce header — token is opaque to clients): %v", kid, alg, err)
-			} else {
-				t.safeLogErrorf("DIAGNOSTIC: Signature verification failed for kid=%s, alg=%s: %v", kid, alg, err)
+		// The signature failed against the (possibly stale) cached key. The
+		// provider may have rotated its signing keys in place, reusing the
+		// same kid (R109): refresh the JWKS once and retry before failing,
+		// otherwise a freshly-rotated token is rejected for up to the JWKS
+		// cache TTL while the stale key remains cached.
+		if freshKey, ferr := t.jwkCache.getPublicKeyFresh(context.Background(), jwksURL, kid, t.httpClient); ferr == nil {
+			if verr := verifySignatureWithKey(token, freshKey, alg); verr == nil {
+				err = nil
 			}
 		}
-		return fmt.Errorf("signature verification failed: %w", err)
+		if err != nil {
+			if !t.suppressDiagnosticLogs {
+				// Microsoft Graph access tokens carry a `nonce` JWT header and are
+				// signed in a proprietary form Microsoft documents as unverifiable
+				// by client applications. They reach this path only when the
+				// per-provider classifier (validateAzureTokens) didn't catch them,
+				// so log at debug to keep the error stream actionable while still
+				// surfacing the cause for diagnostics.
+				if _, isMSProprietary := jwt.Header["nonce"]; isMSProprietary {
+					t.safeLogDebugf("DIAGNOSTIC: Signature verification failed for kid=%s, alg=%s (Microsoft proprietary nonce header — token is opaque to clients): %v", kid, alg, err)
+				} else {
+					t.safeLogErrorf("DIAGNOSTIC: Signature verification failed for kid=%s, alg=%s: %v", kid, alg, err)
+				}
+			}
+			return fmt.Errorf("signature verification failed: %w", err)
+		}
 	}
 
 	if !t.suppressDiagnosticLogs {
@@ -399,9 +483,25 @@ func (t *TraefikOidc) VerifyJWTSignatureAndClaims(jwt *JWT, token string) error
 	isIDToken := t.detectTokenType(jwt, token)
 
 	// Determine expected audience
-	expectedAudience := t.audience // Default to configured audience
+	// Snapshot audience/clientID under metadataMu: DCR rewrites them at
+	// runtime (R137).
+	clientID, _, _, audience, _ := t.clientCredentials()
+	expectedAudience := audience // Default to configured audience
 	if isIDToken {
-		expectedAudience = t.clientID
+		if t.strictAudienceValidation && audience != "" && audience != clientID {
+			// R163: strictAudienceValidation's reject-mismatch promise must
+			// not be silently bypassed by the ID-token classification.
+			// detectTokenType treats any token whose aud contains clientID
+			// as an ID token, which would validate it against clientID
+			// alone — so a token carrying only clientID (and not the
+			// configured audience) always passed the audience check and
+			// strict mode never rejected it. When an explicit, distinct
+			// audience is configured and strict mode is on, enforce the
+			// configured audience even for such tokens.
+			expectedAudience = audience
+		} else {
+			expectedAudience = clientID
+		}
 	}
 	if !t.suppressDiagnosticLogs {
 		if isIDToken {
@@ -500,11 +600,17 @@ func (t *TraefikOidc) refreshToken(rw http.ResponseWriter, req *http.Request, se
 
 	if newToken.IDToken == "" {
 		t.logger.Info("Provider did not return a new ID token during refresh")
+		if !t.persistRotatedRefreshToken(req, rw, session, newToken, "missing ID token") {
+			return false
+		}
 		return false
 	}
 
 	if err = t.verifyToken(newToken.IDToken); err != nil {
 		t.logger.Debug("Failed to verify newly obtained ID token: %v", err)
+		if !t.persistRotatedRefreshToken(req, rw, session, newToken, "failed ID token verification") {
+			return false
+		}
 		return false
 	}
 
@@ -519,19 +625,36 @@ func (t *TraefikOidc) refreshToken(rw http.ResponseWriter, req *http.Request, se
 	claims, err := t.extractClaimsFunc(newToken.IDToken)
 	if err != nil {
 		t.logger.Errorf("refreshToken failed: Failed to extract claims from refreshed token: %v", err)
+		if !t.persistRotatedRefreshToken(req, rw, session, newToken, "failed to extract claims from refreshed token") {
+			return false
+		}
 		return false
 	}
-	userIdentifier, _ := claims[t.userIdentifierClaim].(string)
+	userIdentifier, _ := claimScalarString(claims[t.userIdentifierClaim])
 	if userIdentifier == "" {
 		if t.userIdentifierClaim != "sub" {
-			userIdentifier, _ = claims["sub"].(string)
+			userIdentifier, _ = claimScalarString(claims["sub"])
 		}
 		if userIdentifier == "" {
 			t.logger.Errorf("refreshToken failed: User identifier claim '%s' missing or empty in refreshed token", t.userIdentifierClaim)
+			if !t.persistRotatedRefreshToken(req, rw, session, newToken, "missing user identifier") {
+				return false
+			}
 			return false
 		}
 		t.logger.Debugf("Configured claim '%s' not found in refreshed token, using 'sub' claim as fallback", t.userIdentifierClaim)
 	}
+	// Bind the refreshed token's identity to the one the session already
+	// holds (granted at callback after email gate + isAllowedUser). A
+	// refreshed ID token carrying a different subject must not silently
+	// substitute the user identity mid-session (R106).
+	if prev := session.GetUserIdentifier(); prev != "" && prev != userIdentifier {
+		t.logger.Infof("refreshToken aborted: refreshed token held a different user identifier (%q) than the active session (%q)", userIdentifier, prev)
+		if !t.persistRotatedRefreshToken(req, rw, session, newToken, "user identifier mismatch") {
+			return false
+		}
+		return false
+	}
 	session.SetUserIdentifier(userIdentifier)
 
 	// Get token expiry information for logging
@@ -547,6 +670,9 @@ func (t *TraefikOidc) refreshToken(rw http.ResponseWriter, req *http.Request, se
 	// a refresh (an infinite refresh loop). Keep the previous tokens.
 	if newToken.AccessToken == "" {
 		t.logger.Infof("Provider returned an empty access token during refresh; keeping previous tokens")
+		if !t.persistRotatedRefreshToken(req, rw, session, newToken, "empty access token") {
+			return false
+		}
 		return false
 	}
 
@@ -641,6 +767,28 @@ func (t *TraefikOidc) coordinatedTokenRefresh(req *http.Request, refreshToken st
 // The cache wraps the universal cache, which is Redis-backed in production -
 // so a "hit" here means another Traefik replica refreshed this same token
 // within the last few seconds.
+// persistRotatedRefreshToken saves a refresh token the IdP just rotated during
+// a token exchange, so the session is never left holding a token the exchange
+// already consumed. Rotation IdPs (Zitadel, Authentik, Auth0, ...) invalidate
+// the presented refresh token on every successful exchange regardless of which
+// downstream validation gate (ID token absent, verification failure,
+// identifier mismatch, empty access token) subsequently rejects the response.
+// If the rotated token were not persisted, the next refresh would present the
+// now-consumed token and hit invalid_grant, forcing a full logout.
+func (t *TraefikOidc) persistRotatedRefreshToken(req *http.Request, rw http.ResponseWriter, session *SessionData, newToken *TokenResponse, reason string) bool {
+	if newToken == nil || newToken.RefreshToken == "" {
+		return true // nothing rotated; nothing to persist
+	}
+	session.SetRefreshToken(newToken.RefreshToken)
+	if err := session.Save(req, rw); err != nil {
+		t.logger.Errorf("refreshToken failed to persist rotated refresh token after %s: %v", reason, err)
+		session.SetRefreshToken(newToken.RefreshToken) // keep in-memory for consistency
+		return false
+	}
+	t.logger.Debugf("Persisted rotated refresh token after %s", reason)
+	return true
+}
+
 func (t *TraefikOidc) lookupCachedRefreshResult(sessionID string) (*TokenResponse, bool) {
 	if t.refreshResultCache == nil {
 		return nil, false
@@ -649,8 +797,37 @@ func (t *TraefikOidc) lookupCachedRefreshResult(sessionID string) (*TokenRespons
 	if !ok || v == nil {
 		return nil, false
 	}
-	if tr, ok := v.(*TokenResponse); ok && tr != nil {
-		return tr, true
+	// Cross-backend decode (R159): UniversalCache stores the value locally
+	// as the raw *TokenResponse (stored by cacheRefreshResult) but
+	// serializes it to JSON for any shared backend (e.g. Redis) via
+	// deserialize, which unmarshals into a generic map. The old code only
+	// ever type-asserted *TokenResponse, so every backend read — the
+	// entire cross-replica path — failed the assert and returned nil,
+	// making the advertised refresh dedup silently inert (each replica
+	// still POSTed the refresh token). Normalize any serialized form back
+	// to *TokenResponse.
+	switch val := v.(type) {
+	case *TokenResponse:
+		return val, true
+	case map[string]interface{}, []byte, string:
+		var raw []byte
+		switch tv := v.(type) {
+		case []byte:
+			raw = tv
+		case string:
+			raw = []byte(tv)
+		default:
+			b, err := json.Marshal(v)
+			if err != nil {
+				return nil, false
+			}
+			raw = b
+		}
+		var tr TokenResponse
+		if err := json.Unmarshal(raw, &tr); err != nil {
+			return nil, false
+		}
+		return &tr, true
 	}
 	return nil, false
 }
@@ -685,23 +862,76 @@ const refreshResultCacheTTL = 5 * time.Second
 func (t *TraefikOidc) RevokeToken(token string) {
 	t.tokenCache.Delete(token)
 
+	// Evict any cached positive introspection result so a revoked OPAQUE
+	// access token (which carries no jti and is therefore not covered by
+	// the JTI blacklist below) is not still served an "active" verdict
+	// from the introspection cache after revocation. Next request
+	// re-introspects and sees active=false.
+	if t.introspectionCache != nil {
+		t.introspectionCache.Delete(token)
+	}
+
+	d := blacklistDuration(token)
+
 	if jwt, err := parseJWT(token); err == nil {
 		if jti, ok := jwt.Claims["jti"].(string); ok && jti != "" {
-			expiry := time.Now().Add(24 * time.Hour)
 			if t.tokenBlacklist != nil {
-				t.tokenBlacklist.Set(jti, true, time.Until(expiry))
+				t.tokenBlacklist.Set(jti, true, d)
 				t.logger.Debugf("Locally revoked token JTI %s (added to blacklist)", jti)
 			}
 		}
 	}
 
-	expiry := time.Now().Add(24 * time.Hour)
 	if t.tokenBlacklist != nil {
-		t.tokenBlacklist.Set(token, true, time.Until(expiry))
+		t.tokenBlacklist.Set(token, true, d)
 		t.logger.Debugf("Locally revoked token (added to blacklist)")
 	}
 }
 
+// tokenExpiryUnix extracts the numeric exp claim from a JWT, accepting every
+// representation a decoder or cache backend may produce (float64, json.Number,
+// int). ok is false when the token is not a JWT or carries no usable exp.
+func tokenExpiryUnix(token string) (int64, bool) {
+	jwt, err := parseJWT(token)
+	if err != nil {
+		return 0, false
+	}
+	switch v := jwt.Claims["exp"].(type) {
+	case float64:
+		return int64(v), true
+	case float32:
+		return int64(v), true
+	case json.Number:
+		n, err := v.Int64()
+		if err != nil {
+			return 0, false
+		}
+		return n, true
+	case int64:
+		return v, true
+	case int:
+		return int64(v), true
+	}
+	return 0, false
+}
+
+// blacklistDuration returns how long a revoked token must stay blacklisted.
+// A revoked token remains cryptographically valid until its exp, so the
+// blacklist must cover the entire remaining validity window — otherwise a
+// token with exp more than 24h away could be re-presented (and re-cached)
+// after 24h. A 24h floor keeps short-lived or already-expired tokens
+// blacklisted for a nominal window.
+func blacklistDuration(token string) time.Duration {
+	const minTTL = 24 * time.Hour
+	if exp, ok := tokenExpiryUnix(token); ok {
+		untilExp := time.Until(time.Unix(exp, 0))
+		if untilExp > minTTL {
+			return untilExp
+		}
+	}
+	return minTTL
+}
+
 // RevokeTokenWithProvider revokes a token with the OIDC provider.
 // It sends a revocation request to the provider's revocation endpoint
 // with proper authentication and error recovery if available.
@@ -727,28 +957,40 @@ func (t *TraefikOidc) RevokeTokenWithProvider(token, tokenType string) error {
 	tokenURL := t.tokenURL
 	t.metadataMu.RUnlock()
 
+	// Snapshot the client credentials and related metadata under metadataMu:
+	// DCR (registerWithProvider, main.go) mutates clientID/clientSecret
+	// under metadataMu.Lock concurrently with logout-time revocation, so
+	// reading them here without the lock would be a data race (R134).
+	t.metadataMu.RLock()
+	clientID := t.clientID
+	clientSecret := t.clientSecret
+	clientAuthMethod := t.clientAuthMethod
+	clientAssertion := t.clientAssertion
+	issuerURL := t.issuerURL
+	t.metadataMu.RUnlock()
+
 	data := url.Values{
 		"token":           {token},
 		"token_type_hint": {tokenType},
 	}
 	// client_id is sent in the body for every method except client_secret_basic,
 	// where it is carried in the Authorization header per RFC 6749 §2.3.1.
-	if t.clientAuthMethod != "client_secret_basic" || t.clientAssertion != nil {
-		data.Set("client_id", t.clientID)
+	if clientAuthMethod != "client_secret_basic" || clientAssertion != nil {
+		data.Set("client_id", clientID)
 	}
 
 	useBasicAuth := false
-	if t.clientAssertion != nil {
-		assertion, err := t.clientAssertion.Sign(tokenURL, t.clientID)
+	if clientAssertion != nil {
+		assertion, err := clientAssertion.Sign(tokenURL, clientID)
 		if err != nil {
 			return fmt.Errorf("failed to sign client assertion: %w", err)
 		}
 		data.Set("client_assertion_type", "urn:ietf:params:oauth:client-assertion-type:jwt-bearer")
 		data.Set("client_assertion", assertion)
-	} else if t.clientAuthMethod == "client_secret_basic" {
+	} else if clientAuthMethod == "client_secret_basic" {
 		useBasicAuth = true
 	} else {
-		data.Set("client_secret", t.clientSecret)
+		data.Set("client_secret", clientSecret)
 	}
 
 	req, err := http.NewRequestWithContext(context.Background(), "POST", revocationURL, strings.NewReader(data.Encode()))
@@ -759,16 +1001,13 @@ func (t *TraefikOidc) RevokeTokenWithProvider(token, tokenType string) error {
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 	req.Header.Set("Accept", "application/json")
 	if useBasicAuth {
-		setOAuthBasicAuth(req, t.clientID, t.clientSecret)
+		setOAuthBasicAuth(req, clientID, clientSecret)
 	}
 
 	// Send the request with circuit breaker protection if available
 	var resp *http.Response
 	if t.errorRecoveryManager != nil {
-		// Read issuerURL with RLock for service name
-		t.metadataMu.RLock()
-		serviceName := fmt.Sprintf("token-revocation-%s", t.issuerURL)
-		t.metadataMu.RUnlock()
+		serviceName := fmt.Sprintf("token-revocation-%s", issuerURL)
 		err = t.errorRecoveryManager.ExecuteWithRecovery(context.Background(), serviceName, func() error {
 			var reqErr error
 			resp, reqErr = t.httpClient.Do(req) //nolint:bodyclose // Body is closed in defer after error check
@@ -981,7 +1220,10 @@ func stringListFromClaim(value interface{}) ([]string, bool) {
 	case []interface{}:
 		out := make([]string, 0, len(v))
 		for _, item := range v {
-			if s, ok := item.(string); ok {
+			// Scalar items are stringified (strings and numbers), so a
+			// numeric group/role is preserved instead of being silently
+			// dropped; composite items (maps, nested arrays) are skipped.
+			if s, ok := claimScalarString(item); ok {
 				out = append(out, s)
 			}
 		}
@@ -1000,24 +1242,23 @@ func (t *TraefikOidc) extractGroupsAndRolesFromClaims(claims map[string]interfac
 	var roles []string
 
 	if groupsClaim, exists := claims[t.groupClaimName]; exists {
-		groupsSlice, ok := stringListFromClaim(groupsClaim)
-		if !ok {
-			return nil, nil, fmt.Errorf("%s claim is not an array", t.groupClaimName)
-		}
-		for _, groupStr := range groupsSlice {
-			t.logger.Debugf("Found group from %s claim: %s", t.groupClaimName, groupStr)
-			groups = append(groups, groupStr)
+		if groupsSlice, ok := stringListFromClaim(groupsClaim); ok {
+			groups = append(groups, groupsSlice...)
+			for _, groupStr := range groupsSlice {
+				t.logger.Debugf("Found group from %s claim: %s", t.groupClaimName, groupStr)
+			}
 		}
+		// A malformed/null group claim (numeric scalar, JSON null) is treated
+		// as empty rather than a hard error (R96): one bad claim must not
+		// suppress the valid sibling role signal.
 	}
 
 	if rolesClaim, exists := claims[t.roleClaimName]; exists {
-		rolesSlice, ok := stringListFromClaim(rolesClaim)
-		if !ok {
-			return nil, nil, fmt.Errorf("%s claim is not an array", t.roleClaimName)
-		}
-		for _, roleStr := range rolesSlice {
-			t.logger.Debugf("Found role from %s claim: %s", t.roleClaimName, roleStr)
-			roles = append(roles, roleStr)
+		if rolesSlice, ok := stringListFromClaim(rolesClaim); ok {
+			roles = append(roles, rolesSlice...)
+			for _, roleStr := range rolesSlice {
+				t.logger.Debugf("Found role from %s claim: %s", t.roleClaimName, roleStr)
+			}
 		}
 	}
 

token_resilience.go

@@ -118,18 +118,15 @@ func (trm *TokenResilienceManager) ExecuteTokenOperation(ctx context.Context, op
 		return fn()
 	}
 
-	// Compose resilience mechanisms
+	// Compose resilience mechanisms. Retry is the INNER layer (around the
+	// operation) and the circuit breaker is the OUTER layer, so the breaker
+	// observes one aggregate result per logical operation rather than one
+	// failure per retry attempt (which would trip it prematurely — e.g.
+	// maxFailures=3 + 3 retries opening the breaker on a single brief
+	// outage, failing the very next genuine request). R106.
 	var finalOperation func() error = fn
 
-	// Wrap with circuit breaker if enabled
-	if trm.config.CircuitBreakerEnabled && trm.circuitBreaker != nil {
-		originalOp := finalOperation
-		finalOperation = func() error {
-			return trm.circuitBreaker.ExecuteWithContext(ctx, originalOp)
-		}
-	}
-
-	// Wrap with retry if enabled
+	// Wrap with retry if enabled (innermost layer)
 	if trm.config.RetryEnabled && trm.retryExecutor != nil {
 		originalOp := finalOperation
 		if singleUse {
@@ -143,6 +140,14 @@ func (trm *TokenResilienceManager) ExecuteTokenOperation(ctx context.Context, op
 		}
 	}
 
+	// Wrap with circuit breaker if enabled (outermost layer)
+	if trm.config.CircuitBreakerEnabled && trm.circuitBreaker != nil {
+		originalOp := finalOperation
+		finalOperation = func() error {
+			return trm.circuitBreaker.ExecuteWithContext(ctx, originalOp)
+		}
+	}
+
 	err := finalOperation()
 
 	if err != nil && trm.logger != nil {
@@ -174,7 +179,12 @@ func (trm *TokenResilienceManager) ExecuteTokenRefresh(ctx context.Context, t *T
 	var result *TokenResponse
 	var err error
 
-	err = trm.ExecuteTokenOperation(ctx, "token_refresh", false, func() error {
+	// Refresh is single-use (like the auth-code exchange): a client-side timeout
+	// may mean the provider already processed AND rotated the refresh token, so
+	// re-presenting it on a retry surfaces invalid_grant and the session is
+	// cleared — escalating a transient timeout into a full logout. Single-use
+	// retries only on "never sent" errors (connect/dial), never on timeout.
+	err = trm.ExecuteTokenOperation(ctx, "token_refresh", true, func() error {
 		// Call exchangeTokens directly to avoid recursion back to getNewTokenWithRefreshToken
 		// which would call ExecuteTokenRefresh again, causing infinite loop (issue #67)
 		result, err = t.exchangeTokens(ctx, "refresh_token", refreshToken, "", "")

token_validation_rs.go

@@ -15,6 +15,7 @@ package traefikoidc
 import (
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"strings"
 	"time"
 )
@@ -81,6 +82,19 @@ func (t *TraefikOidc) accessTokenUnexpired(token string) bool {
 // validateTokenExpiryRS is the requestState-aware variant of validateTokenExpiry.
 // Reads rs.refreshToken instead of session.GetRefreshToken() (4 RLocks avoided).
 func (t *TraefikOidc) validateTokenExpiryRS(rs *requestState, token string) (bool, bool, bool) {
+	// Defense-in-depth (F2/R133): this is the final authenticated gate.
+	// Every current caller has already passed the blacklist check via
+	// verifyToken, but guard independently so a revoked-but-still-cached
+	// token can never be served authenticated if the call order changes.
+	if t.tokenBlacklist != nil {
+		if b, ok := t.tokenBlacklist.Get(token); ok && b != nil {
+			if rs.refreshToken != "" {
+				return false, true, false
+			}
+			return false, false, true
+		}
+	}
+
 	cachedClaims, found := t.tokenCache.Get(token)
 	if !found {
 		t.logger.Debug("Claims not found in cache after successful token verification")
@@ -102,7 +116,13 @@ func (t *TraefikOidc) validateTokenExpiryRS(rs *requestState, token string) (boo
 	expTimeObj := time.Unix(int64(expClaim), 0)
 	nowObj := time.Now()
 
-	if expTimeObj.Before(nowObj) {
+	// Apply the same clock-skew leeway as jwt.Verify's verifyExpiration
+	// (ClockSkewToleranceFuture). This is the final auth gate run after
+	// successful signature verification; without the leeway a token
+	// within the 2-minute post-exp window was granted by Verify but
+	// downgraded to here as expired, forcing a needless refresh or
+	// re-auth (R124).
+	if nowObj.After(expTimeObj.Add(ClockSkewToleranceFuture)) {
 		if rs.refreshToken != "" {
 			return false, true, false
 		}
@@ -177,6 +197,19 @@ func (t *TraefikOidc) validateStandardTokensRS(rs *requestState) (bool, bool, bo
 					}
 					return false, false, true
 				}
+				// A definitive 4xx from the introspection endpoint (e.g. 401
+				// for an unknown/revoked token) means the token itself is bad,
+				// not that the endpoint transiently failed. Treat it as
+				// invalid (refresh) rather than falling through to
+				// ID-token-only auth, which would authenticate a revoked
+				// opaque token (R156).
+				var httpErr *HTTPError
+				if errors.As(err, &httpErr) && httpErr.StatusCode >= 400 && httpErr.StatusCode < 500 {
+					if rs.refreshToken != "" {
+						return false, true, false
+					}
+					return false, false, true
+				}
 				if t.requireTokenIntrospection {
 					if rs.refreshToken != "" {
 						return false, true, false
@@ -231,7 +264,9 @@ func (t *TraefikOidc) validateStandardTokensRS(rs *requestState) (bool, bool, bo
 	// JWT access token present.
 	accessTokenValid := false
 	lenientAudienceOnly := false
+	var accessVerifyErr error
 	if err := t.verifyToken(rs.accessToken); err != nil {
+		accessVerifyErr = err
 		errMsg := err.Error()
 		if strings.Contains(errMsg, "invalid audience") || strings.Contains(errMsg, "audience") {
 			if t.strictAudienceValidation {
@@ -298,6 +333,21 @@ func (t *TraefikOidc) validateStandardTokensRS(rs *requestState) (bool, bool, bo
 	if accessTokenValid {
 		return t.validateTokenExpiryRS(rs, rs.accessToken)
 	}
+	// Access token is a JWT whose verification failed, yet the session's
+	// ID token is still valid. If the failure was specifically EXPIRY —
+	// verifyToken checks the signature before exp, so "token has expired"
+	// implies the signature and other claims validated — the access token
+	// is unusable at the upstream resource. Refresh to obtain a fresh one
+	// rather than forwarding a stale access token (R131). Without this an
+	// expired access token (with a still-valid ID token) was authenticated
+	// with needsRefresh=false and forwarded as-is until the ID token
+	// itself neared expiry, giving the backend an expired bearer token.
+	if accessVerifyErr != nil && strings.Contains(accessVerifyErr.Error(), "token has expired") {
+		if rs.refreshToken != "" {
+			return true, true, false
+		}
+		return false, false, true
+	}
 	return t.validateTokenExpiryRS(rs, rs.idToken)
 }
 
@@ -326,6 +376,41 @@ func (t *TraefikOidc) validateAzureTokensRS(rs *requestState) (bool, bool, bool)
 					}
 					return t.validateTokenExpiryRS(rs, rs.idToken)
 				}
+				// No ID token to corroborate the Azure token. Its signature
+				// can't be verified client-side, but it still carries exp;
+				// authenticate only while unexpired. Previously this
+				// returned authenticated=true with no expiry check, so an
+				// expired (or unparseable) Azure access token authenticated
+				// indefinitely until the session itself expired (R129).
+				if claims, err := extractClaims(rs.accessToken); err != nil {
+					if rs.refreshToken != "" {
+						return false, true, false
+					}
+					return false, false, true
+				} else {
+					// Defense-in-depth (mirrors validateTokenExpiryRS): a
+					// revoked-but-still-cached token must not authenticate
+					// through this unverifiable branch either (R147).
+					if t.tokenBlacklist != nil {
+						if b, ok := t.tokenBlacklist.Get(rs.accessToken); ok && b != nil {
+							if rs.refreshToken != "" {
+								return false, true, false
+							}
+							return false, false, true
+						}
+					}
+					// exp must be present and numeric to establish the token
+					// is current; an unverifiable token with no (or
+					// non-numeric) exp authenticates with zero verification,
+					// so fail closed when it can't be bounded (R130).
+					exp, ok := claims["exp"].(float64)
+					if !ok || time.Now().After(time.Unix(int64(exp), 0).Add(ClockSkewToleranceFuture)) {
+						if rs.refreshToken != "" {
+							return false, true, false
+						}
+						return false, false, true
+					}
+				}
 				return true, false, false
 			}
 			if err := t.verifyToken(rs.accessToken); err != nil {
@@ -349,7 +434,17 @@ func (t *TraefikOidc) validateAzureTokensRS(rs *requestState) (bool, bool, bool)
 		if rs.idToken != "" {
 			return t.validateTokenExpiryRS(rs, rs.idToken)
 		}
-		return true, false, false
+		// Opaque access token with no ID token to corroborate it. Do not
+		// authenticate on an unverified (or unverifiable) token: refresh
+		// if a refresh token is available, otherwise force
+		// re-authentication. Mirrors validateStandardTokensRS, which
+		// documents this exact decision ("Do NOT authenticate on an
+		// unverified token"). The previous `return true, false, false`
+		// accepted any opaque value here with no verification (R99).
+		if rs.refreshToken != "" {
+			return false, true, false
+		}
+		return false, false, true
 	}
 
 	if rs.idToken != "" {

url_helpers.go

@@ -75,8 +75,11 @@ func pathExcluded(requestPath, excluded string) bool {
 // Returns:
 //   - The fully constructed authorization URL string.
 func (t *TraefikOidc) buildAuthURL(redirectURL, state, nonce, codeChallenge string) string {
+	// Snapshot clientID/audience under metadataMu: DCR rewrites them at
+	// runtime (R137).
+	clientID, _, _, audience, _ := t.clientCredentials()
 	params := url.Values{}
-	params.Set("client_id", t.clientID)
+	params.Set("client_id", clientID)
 	params.Set("response_type", "code")
 	params.Set("redirect_uri", redirectURL)
 	params.Set("state", state)
@@ -86,9 +89,9 @@ func (t *TraefikOidc) buildAuthURL(redirectURL, state, nonce, codeChallenge stri
 	// This allows access tokens to have the correct audience claim
 	// Only add if audience is configured and different from client_id
 	// ID tokens will always have aud=client_id per OIDC spec
-	if t.audience != "" && t.audience != t.clientID {
-		params.Set("audience", t.audience)
-		t.logger.Debugf("Adding audience parameter to authorize URL: %s", t.audience)
+	if audience != "" && audience != clientID {
+		params.Set("audience", audience)
+		t.logger.Debugf("Adding audience parameter to authorize URL: %s", audience)
 	}
 
 	if t.enablePKCE && codeChallenge != "" {
@@ -224,6 +227,22 @@ func (t *TraefikOidc) buildAuthURL(redirectURL, state, nonce, codeChallenge stri
 //
 // Returns:
 //   - The fully constructed URL string with appended query parameters.
+//
+// preserveBaseQuery seeds url parameters from the base URL's pre-existing
+// query string, without overriding authoritative plugin-supplied params.
+// Some IdPs embed client_id or template params in their discovered
+// authorization/end-session endpoints; overwriting RawQuery dropped them
+// (R101).
+func (t *TraefikOidc) preserveBaseQuery(u *url.URL, params url.Values) {
+	for k, vs := range u.Query() {
+		if params.Get(k) == "" {
+			for _, v := range vs {
+				params.Add(k, v)
+			}
+		}
+	}
+}
+
 func (t *TraefikOidc) buildURLWithParams(baseURL string, params url.Values) string {
 	if baseURL != "" {
 		if strings.HasPrefix(baseURL, "http://") || strings.HasPrefix(baseURL, "https://") {
@@ -259,6 +278,7 @@ func (t *TraefikOidc) buildURLWithParams(baseURL string, params url.Values) stri
 			return ""
 		}
 
+		t.preserveBaseQuery(resolvedURL, params)
 		resolvedURL.RawQuery = params.Encode()
 		return resolvedURL.String()
 	}
@@ -274,6 +294,7 @@ func (t *TraefikOidc) buildURLWithParams(baseURL string, params url.Values) stri
 		return ""
 	}
 
+	t.preserveBaseQuery(u, params)
 	u.RawQuery = params.Encode()
 	return u.String()
 }
@@ -359,6 +380,14 @@ func (t *TraefikOidc) validateDiscoveredEndpoint(urlStr string, allowLoopback bo
 	if u.Scheme != "https" && u.Scheme != "http" {
 		return fmt.Errorf("disallowed URL scheme: %q", u.Scheme)
 	}
+	// Pin the discovered endpoint's scheme to the provider's own scheme. A
+	// provider served over HTTPS must hand out HTTPS endpoints; a legacy or
+	// poisoned discovery document that downgrades a credential-bearing
+	// endpoint (client_secret, tokens) to plaintext HTTP would otherwise be
+	// used as-is, shipping secrets over an unauthenticated channel (R146).
+	if u.Scheme == "http" && t.providerUsesHTTPS() {
+		return fmt.Errorf("discovered endpoint uses plaintext http while the provider is https; refusing scheme downgrade")
+	}
 	if u.Host == "" {
 		return fmt.Errorf("missing host in URL")
 	}
@@ -371,6 +400,15 @@ func (t *TraefikOidc) validateDiscoveredEndpoint(urlStr string, allowLoopback bo
 		case ip.IsPrivate() && !t.allowPrivateIPAddresses:
 			return fmt.Errorf("endpoint host is a private address: %s", ip)
 		}
+	} else if err := t.validateHost(u.Hostname()); err != nil && !(allowLoopback && isLoopbackHost(u.Hostname())) {
+		// Name-based hosts (localhost, metadata.google.internal, any
+		// hostname) bypass the IP-literal checks above; run the hostname
+		// SSRF guard so a discovery doc pointing at such a host is
+		// rejected (R97). Loopback names (localhost) are permitted when
+		// allowLoopback is set, mirroring the IP-literal branch; hard
+		// metadata-service names (metadata.google.internal) are never
+		// allowed because they are not loopback.
+		return fmt.Errorf("discovered endpoint host is not allowed: %w", err)
 	}
 	if strings.Contains(u.Path, "..") {
 		return fmt.Errorf("path traversal detected in URL path")
@@ -382,6 +420,14 @@ func (t *TraefikOidc) validateDiscoveredEndpoint(urlStr string, allowLoopback bo
 // Used to pin the credential-bearing introspection endpoint to the operator-
 // configured provider so a poisoned discovery document cannot redirect the
 // client secret to an attacker-controlled host.
+// providerUsesHTTPS reports whether the operator-configured provider URL is
+// served over HTTPS. Used to pin discovered endpoint schemes.
+func (t *TraefikOidc) providerUsesHTTPS() bool {
+	t.metadataMu.RLock()
+	defer t.metadataMu.RUnlock()
+	return t.providerURL != "" && strings.HasPrefix(strings.ToLower(t.providerURL), "https://")
+}
+
 func sameHost(a, b string) bool {
 	ua, erra := url.Parse(a)
 	ub, errb := url.Parse(b)
@@ -454,3 +500,24 @@ func (t *TraefikOidc) validateHost(host string) error {
 
 	return nil
 }
+
+// redactCallbackURL returns the callback URL with the one-time
+// authorization code (and state) query values redacted. The single-use
+// code is a quiet credential: logging the full callback URL (as the
+// per-request Debug line and the CSRF-failure Error line did) would
+// publish it into the log pipeline (R153). Malformed URLs are returned
+// unchanged.
+func redactCallbackURL(rawURL string) string {
+	u, err := url.Parse(rawURL)
+	if err != nil {
+		return rawURL
+	}
+	q := u.Query()
+	for _, k := range []string{"code", "state"} {
+		if q.Get(k) != "" {
+			q.Set(k, "[REDACTED]")
+		}
+	}
+	u.RawQuery = q.Encode()
+	return u.String()
+}