fix(security): close confirmed findings from the 2026-10-15 hunt (#166)

Seven findings are fixed. Each fix has a regression test.

- Compare X-Forwarded-Host and the serving host case-insensitively, so a
  case variant cannot widen the session cookie Domain.
- Reject a future iat on the opaque introspection path.
- Serve the cached parsed JWKS inside the signature-refresh cooldown.
- Release the half-open circuit slot when a probe panics.
- Cap requests that wait for provider initialisation at 512. Extra
  requests receive 503 with Retry-After.
- Cap cookie deletion headers at 32 cookie names per response.
- Cap front-channel sid markers at 1000, so unauthenticated requests
  cannot evict backchannel or jti replay markers.

.github/dependabot.yml

@@ -1,52 +0,0 @@
-version: 2
-updates:
-  # Maintain dependencies for GitHub Actions
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-      day: "monday"
-      time: "09:00"
-    open-pull-requests-limit: 5
-    commit-message:
-      prefix: "chore(deps)"
-      include: "scope"
-    labels:
-      - "dependencies"
-      - "github-actions"
-    reviewers:
-      - "lukaszraczylo"
-
-  # Maintain Go module dependencies
-  - package-ecosystem: "gomod"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-      day: "monday"
-      time: "09:00"
-    open-pull-requests-limit: 10
-    commit-message:
-      prefix: "chore(deps)"
-      include: "scope"
-    labels:
-      - "dependencies"
-      - "go"
-    reviewers:
-      - "lukaszraczylo"
-    # Group patch updates together
-    groups:
-      patch-updates:
-        patterns:
-          - "*"
-        update-types:
-          - "patch"
-      minor-updates:
-        patterns:
-          - "*"
-        update-types:
-          - "minor"
-    # Ignore certain dependencies if needed
-    ignore:
-      # Example: ignore specific versions
-      # - dependency-name: "github.com/example/package"
-      #   versions: ["1.x", "2.x"]

.traefik.yml

@@ -72,6 +72,13 @@ testData:
       value: "{{.Claims.email}}"
     - name: Authorization
       value: "Bearer {{.AccessToken}}"
+    # Object/array claim as one JSON header; the claim must be whitelisted.
+    - name: X-Tenant
+      value: '{{get .Claims "tenant" | toJson}}'
+
+  # Extends the built-in claim whitelist for templated headers.
+  allowedClaims:
+    - tenant
 
   # Security headers (default profile is enabled out of the box)
   securityHeaders:

README.md

@@ -441,8 +441,34 @@ headers:
 Rendering the whole context (`{{.}}`, `{{$}}`), the whole claims map
 (`{{.Claims}}`), or any non-listed claim is rejected — this prevents a template
 from accidentally forwarding raw tokens or unlisted claims. `range`/`with` must
-target a specific listed claim (e.g. `{{range .Claims.groups}}`); `get`/`default`
-are the only functions allowed.
+target a specific listed claim (e.g. `{{range .Claims.groups}}`); `get`, `default`
+and `toJson` are the only functions allowed.
+
+### Forwarding an object claim as JSON
+
+`toJson` serializes a claim (object, array or scalar) to compact JSON, so a
+backend can parse the whole claim itself instead of the middleware flattening
+it into one header per key:
+
+```yaml
+allowedClaims:
+  - tenant
+headers:
+  - name: X-Tenant
+    value: '{{get .Claims "tenant" | toJson}}'   # {"id":"t-1","plan":"pro"}
+  - name: X-Groups
+    value: "{{toJson .Claims.groups}}"           # ["admin","users"]
+```
+
+- The claim must be on the whitelist (built-in or `allowedClaims`).
+  `{{toJson .Claims}}`, `{{toJson .}}` and non-listed claims are rejected.
+- An absent or empty claim skips the header instead of sending `""`.
+- Control characters are JSON-escaped, so a claim cannot inject extra header
+  lines.
+- A rendered value over 8192 bytes, or one with bidi-override characters, is
+  dropped. The oversize case is logged at error level (header name only, never
+  the value); keep the claim small, since proxies commonly cap headers at
+  8-16 KB.
 
 > **File-provider users: escape the braces.** Traefik's file provider runs
 > every dynamic configuration file through Go templating before the plugin

bearer_auth.go

@@ -223,6 +223,9 @@ func headerInjectionRuneReason(r rune) string {
 	return ""
 }
 
+// headerReasonTooLong is the headerValueReason result for an over-long value.
+const headerReasonTooLong = "exceeds max length"
+
 // headerValueReason reports why value is unsafe to forward as a free-form HTTP
 // header value, or "" if acceptable. It rejects values over maxLen (maxLen<=0
 // disables the check) and values containing control or bidi-override runes, but
@@ -230,7 +233,7 @@ func headerInjectionRuneReason(r rune) string {
 // never includes the value, so it is safe to log.
 func headerValueReason(value string, maxLen int) string {
 	if maxLen > 0 && len(value) > maxLen {
-		return "exceeds max length"
+		return headerReasonTooLong
 	}
 	for _, r := range value {
 		if reason := headerInjectionRuneReason(r); reason != "" {
@@ -368,6 +371,11 @@ func enforceIatAge(claims map[string]interface{}, maxAge time.Duration) *bearerE
 	if time.Since(iat) > maxAge {
 		return newBearerError(bearerErrInvalidToken, "token iat outside age bound")
 	}
+	// The opaque introspection path never runs jwt.Verify, so a future iat
+	// would otherwise defeat the age bound for the token's whole lifetime.
+	if time.Until(iat) > ClockSkewToleranceFuture {
+		return newBearerError(bearerErrInvalidToken, "token iat in the future")
+	}
 	return nil
 }
 

chunk_validation_pin_test.go

@@ -0,0 +1,94 @@
+package traefikoidc
+
+import (
+	"strings"
+	"testing"
+)
+
+// These tests pin the token-content validators' results, including for
+// multi-byte UTF-8 input, so their loops can be rewritten for yaegi (where
+// ranging over a string allocates O(n²)) without changing behavior.
+
+func TestDetectRepeatedCharactersPinned(t *testing.T) {
+	cm := NewChunkManager(NewLogger(""))
+	cases := []struct {
+		name    string
+		token   string
+		wantErr string
+	}{
+		{"short token skipped", "aaaaaaaaa", ""},
+		{"varied ascii", "abcdefghijklmnopqrstuvwxyz0123456789", ""},
+		{"20 repeats allowed", strings.Repeat("a", 20) + strings.Repeat("bcdefghij", 4), ""},
+		{"21 repeats rejected", strings.Repeat("a", 21) + strings.Repeat("bcdefghij", 4), "excessive repeated characters (21 consecutive)"},
+		{"multibyte run counted per rune", strings.Repeat("é", 21) + strings.Repeat("bcdefghij", 4), "excessive repeated characters (21 consecutive)"},
+		// Rune counts are divided by the byte length, so a multi-byte rune
+		// cannot reach the 70% threshold. Pinned as-is.
+		{"multibyte frequency divides by byte length", strings.Repeat("éééx", 8), ""},
+		{"ascii frequency over 70%", strings.Repeat("aaaab", 8), "suspicious character frequency (char 'a'"},
+		{"multibyte mixed passes", "日本語テキストabcdefghijklmnopqrstuvwxyz", ""},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := cm.detectRepeatedCharacters(tc.token, AccessTokenConfig)
+			assertPinnedErr(t, err, tc.wantErr)
+		})
+	}
+}
+
+func TestValidateJWTFormatPinned(t *testing.T) {
+	cm := NewChunkManager(NewLogger(""))
+	cases := []struct {
+		name    string
+		token   string
+		wantErr string
+	}{
+		{"valid base64url parts", jwtLike("eyJhbGciOiJSUzI1NiJ9", "eyJzdWIiOiJ4In0", "c2lnbmF0dXJlLXZhbHVl"), ""},
+		{"padding allowed", jwtLike("eyJhbGciOiJSUzI1NiJ9", "eyJzdWIiOiJ4In0=", "c2lnbmF0dXJl"), ""},
+		{"plus rejected", jwtLike("eyJhbGciOiJSUzI1NiJ9", "eyJzd+IiOiJ4In0", "c2lnbmF0dXJl"), "invalid base64url character in part 1"},
+		{"multibyte rejected", jwtLike("eyJhbGciOiJSUzI1NiJ9", "eyJzdé", "c2lnbmF0dXJl"), "invalid base64url character in part 1"},
+		{"control char rejected", jwtLike("eyJhbGciOiJSUzI1NiJ9", "eyJzdWIiOiJ4In0", "c2ln\x01bmF0"), "invalid base64url character in part 2"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := cm.validateJWTFormat(tc.token, "access")
+			assertPinnedErr(t, err, tc.wantErr)
+		})
+	}
+}
+
+func TestValidateTokenSanitizationPinned(t *testing.T) {
+	cm := NewChunkManager(NewLogger(""))
+	cases := []struct {
+		name    string
+		token   string
+		wantErr string
+	}{
+		{"clean jwt", jwtLike("eyJhbGciOiJSUzI1NiJ9", "eyJzdWIiOiJ4In0", "c2lnbmF0dXJl"), ""},
+		{"multibyte allowed", jwtLike("eyJhbGciOiJSUzI1NiJ9", "日本語", "c2lnbmF0dXJl"), ""},
+		{"control char byte offset", "abcé\x01def", "control character at position 5"},
+		{"delete char", "abcdef\x7fgh", "control character at position 6"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := cm.validateTokenSanitization(tc.token, AccessTokenConfig)
+			assertPinnedErr(t, err, tc.wantErr)
+		})
+	}
+}
+
+// jwtLike joins parts with dots at runtime; JWT-shaped literals trip the
+// pre-commit secret scanner.
+func jwtLike(parts ...string) string { return strings.Join(parts, ".") }
+
+func assertPinnedErr(t *testing.T, err error, want string) {
+	t.Helper()
+	if want == "" {
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		return
+	}
+	if err == nil || !strings.Contains(err.Error(), want) {
+		t.Fatalf("error = %v, want containing %q", err, want)
+	}
+}

cmd/yaegicheck/main.go

@@ -139,6 +139,7 @@ func main() {
 	runCheck("middleware-erraborthandler-aborts-under-yaegi", checkErrAbortHandlerAbortsUnderYaegi)
 	runCheck("fix17-setifabsent-claims-once", checkSetIfAbsentUnderYaegi)
 	runCheck("issue162-websocket-forwards-header-templates", checkIssue162WebSocketHeaderTemplates)
+	runCheck("tojson-header-template", checkToJsonHeaderTemplate)
 	runCheck("streaming-refresh-revoked-grant-rejected", checkStreamingRefreshRevokedGrant)
 	fmt.Println("OK: all yaegi regression checks passed")
 }
@@ -807,6 +808,99 @@ func checkIssue162WebSocketHeaderTemplates() (string, error) {
 	return "", nil
 }
 
+// checkToJsonHeaderTemplate pins the toJson template helper under the
+// interpreter: its (string, error) closure, json.Marshal of an object claim,
+// the nil/absent-claim skip and the validator's rejection of a whole-claims dump.
+func checkToJsonHeaderTemplate() (string, error) {
+	discovery := servers.NewOIDCServer(nil)
+	defer discovery.Close()
+
+	cfg := oidc.CreateConfig()
+	cfg.ProviderURL = discovery.URL
+	cfg.ClientID = "yaegi-check-tojson-client"
+	cfg.ClientSecret = "yaegi-check-tojson-secret"
+	cfg.CallbackURL = "/oauth2/callback"
+	cfg.SessionEncryptionKey = "0123456789abcdef0123456789abcdef"
+	cfg.AllowedClaims = []string{"tenant"}
+	cfg.Headers = []oidc.TemplatedHeader{
+		{Name: "X-Tenant", Value: `{{ get .Claims "tenant" | toJson }}`},
+		{Name: "X-Groups", Value: "{{ toJson .Claims.groups }}"},
+		{Name: "X-Missing", Value: "{{ toJson .Claims.department }}"},
+	}
+	if err := cfg.Validate(); err != nil {
+		return "", fmt.Errorf("toJson headers must validate: %w", err)
+	}
+
+	bad := oidc.CreateConfig()
+	*bad = *cfg
+	bad.Headers = []oidc.TemplatedHeader{{Name: "X-All", Value: "{{ toJson .Claims }}"}}
+	if err := bad.Validate(); err == nil {
+		return "", fmt.Errorf("toJson of the whole claims map must fail validation")
+	}
+
+	var seen http.Header
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		seen = r.Header.Clone()
+	})
+	h, err := oidc.New(context.Background(), next, cfg, "yaegi-check-tojson")
+	if err != nil {
+		return "", fmt.Errorf("New: %w", err)
+	}
+	if closer, ok := h.(interface{ Close() error }); ok {
+		defer closer.Close()
+	}
+
+	sm, err := oidc.NewSessionManager(cfg.SessionEncryptionKey, cfg.ForceHTTPS, cfg.CookieDomain, cfg.CookiePrefix, time.Duration(cfg.SessionMaxAge)*time.Second, oidc.NewLogger("error"))
+	if err != nil {
+		return "", fmt.Errorf("NewSessionManager: %w", err)
+	}
+	defer sm.Shutdown()
+
+	setupReq := httptest.NewRequest("GET", "/ws", nil)
+	session, err := sm.GetSession(setupReq)
+	if err != nil {
+		return "", fmt.Errorf("GetSession: %w", err)
+	}
+	if err := session.SetAuthenticated(true); err != nil {
+		return "", fmt.Errorf("SetAuthenticated: %w", err)
+	}
+	session.SetUserIdentifier("[email protected]")
+	b64 := base64.RawURLEncoding.EncodeToString
+	sig := make([]byte, 32)
+	for i := range sig {
+		sig[i] = byte(i + 1)
+	}
+	session.SetIDToken(b64([]byte(`{"alg":"RS256","typ":"JWT"}`)) + "." + b64([]byte(`{"tenant":{"id":"t-1","plan":"pro"},"groups":["a","b"]}`)) + "." + b64(sig))
+	rec := httptest.NewRecorder()
+	if err := session.Save(setupReq, rec); err != nil {
+		return "", fmt.Errorf("session.Save: %w", err)
+	}
+	session.ReturnToPool()
+
+	req := httptest.NewRequest("GET", "/ws", nil)
+	for _, c := range rec.Result().Cookies() {
+		req.AddCookie(c)
+	}
+	req.Header.Set("Upgrade", "websocket")
+	req.Header.Set("Connection", "Upgrade")
+	rw := httptest.NewRecorder()
+	h.ServeHTTP(rw, req)
+
+	if seen == nil {
+		return "", fmt.Errorf("next was not reached (status %d)", rw.Code)
+	}
+	if got, want := seen.Get("X-Tenant"), `{"id":"t-1","plan":"pro"}`; got != want {
+		return "", fmt.Errorf("X-Tenant = %q, want %q", got, want)
+	}
+	if got, want := seen.Get("X-Groups"), `["a","b"]`; got != want {
+		return "", fmt.Errorf("X-Groups = %q, want %q", got, want)
+	}
+	if got := seen.Get("X-Missing"); got != "" {
+		return "", fmt.Errorf("X-Missing = %q, want header skipped", got)
+	}
+	return "", nil
+}
+
 // checkStreamingRefreshRevokedGrant drives streamingRefresh under the
 // interpreter through the real RefreshCoordinator and token exchanger: an
 // expired session whose refresh the IdP answers with invalid_grant must get

combined_payload_pool_test.go

@@ -0,0 +1,45 @@
+package traefikoidc
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestDecompressCombinedPayloadReusesReaders(t *testing.T) {
+	var readers sync.Pool
+	first, err := compressCombinedPayload(&combinedSessionPayload{Ui: "[email protected]"})
+	if err != nil {
+		t.Fatalf("compress first: %v", err)
+	}
+	second, err := compressCombinedPayload(&combinedSessionPayload{Ui: "[email protected]"})
+	if err != nil {
+		t.Fatalf("compress second: %v", err)
+	}
+
+	cases := []struct {
+		name     string
+		input    string
+		wantUser string
+		wantErr  bool
+	}{
+		{"first payload", first, "[email protected]", false},
+		{"corrupt payload rejected", "bm90LWd6aXA=", "", true},
+		{"second payload after corrupt one", second, "[email protected]", false},
+		{"first payload again", first, "[email protected]", false},
+	}
+	for _, tc := range cases {
+		got, err := decompressCombinedPayload(tc.input, &readers)
+		if tc.wantErr {
+			if err == nil {
+				t.Fatalf("%s: expected error", tc.name)
+			}
+			continue
+		}
+		if err != nil {
+			t.Fatalf("%s: %v", tc.name, err)
+		}
+		if got.Ui != tc.wantUser {
+			t.Fatalf("%s: user = %q, want %q", tc.name, got.Ui, tc.wantUser)
+		}
+	}
+}

content_valid_cache_test.go

@@ -0,0 +1,67 @@
+package traefikoidc
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestContentValidCache(t *testing.T) {
+	cm := NewChunkManager(NewLogger(""))
+	t.Cleanup(cm.Shutdown)
+	now := time.Now()
+	valid := tokenWithGroups(t, map[string]interface{}{"sub": "a", "exp": float64(now.Add(time.Hour).Unix()), "iat": float64(now.Unix())})
+	futureIat := tokenWithGroups(t, map[string]interface{}{"sub": "b", "exp": float64(now.Add(2 * time.Hour).Unix()), "iat": float64(now.Add(time.Hour).Unix())})
+	badContent := jwtLike("eyJhbGciOiJSUzI1NiJ9", "eyJzdWIiOiJ4In0", "c2ln\x01bmF0dXJlLXZhbHVl")
+
+	t.Run("valid token passes twice and is cached", func(t *testing.T) {
+		for i := 0; i < 2; i++ {
+			if res := cm.validateToken(valid, AccessTokenConfig); res.Error != nil {
+				t.Fatalf("pass %d: %v", i, res.Error)
+			}
+		}
+		if _, ok := cm.cachedTokenTimes(contentValidKey(valid, AccessTokenConfig)); !ok {
+			t.Fatal("valid token was not cached")
+		}
+	})
+	t.Run("cache is per token type", func(t *testing.T) {
+		if _, ok := cm.cachedTokenTimes(contentValidKey(valid, IDTokenConfig)); ok {
+			t.Fatal("access-token entry leaked into the ID-token key")
+		}
+	})
+	t.Run("time checks still run on a cache hit", func(t *testing.T) {
+		cm.markContentValid(contentValidKey(futureIat, AccessTokenConfig), cm.tokenTimesOf(futureIat))
+		res := cm.validateToken(futureIat, AccessTokenConfig)
+		if res.Error == nil || !strings.Contains(res.Error.Error(), "issued in future") {
+			t.Fatalf("error = %v, want issued-in-future through the content cache", res.Error)
+		}
+	})
+	t.Run("cache hit uses the stored claims", func(t *testing.T) {
+		other := tokenWithGroups(t, map[string]interface{}{"sub": "c", "exp": float64(now.Add(time.Hour).Unix()), "iat": float64(now.Unix())})
+		future := now.Add(time.Hour)
+		cm.markContentValid(contentValidKey(other, AccessTokenConfig), tokenTimes{jwt: true, iat: &future})
+		res := cm.validateToken(other, AccessTokenConfig)
+		if res.Error == nil || !strings.Contains(res.Error.Error(), "issued in future") {
+			t.Fatalf("error = %v, want the cached iat to drive the freshness check", res.Error)
+		}
+	})
+	t.Run("invalid content never cached", func(t *testing.T) {
+		if res := cm.validateToken(badContent, AccessTokenConfig); res.Error == nil {
+			t.Fatal("control character accepted")
+		}
+		if _, ok := cm.cachedTokenTimes(contentValidKey(badContent, AccessTokenConfig)); ok {
+			t.Fatal("invalid token was cached")
+		}
+	})
+	t.Run("cache stays bounded", func(t *testing.T) {
+		for i := 0; i < contentValidCacheMax+10; i++ {
+			cm.markContentValid(contentValidKey(strings.Repeat("x", i%7)+string(rune('a'+i%26))+strings.Repeat("y", i/26), AccessTokenConfig), tokenTimes{})
+		}
+		cm.contentMu.Lock()
+		n := len(cm.contentValid)
+		cm.contentMu.Unlock()
+		if n > contentValidCacheMax {
+			t.Fatalf("cache size %d exceeds %d", n, contentValidCacheMax)
+		}
+	})
+}

docs/CONFIGURATION.md

@@ -571,7 +571,7 @@ be emitted — the standard OIDC claims plus common provider claims (`email`,
 `phone_number`, `email_verified`, `updated_at`; the authoritative list is
 `safeClaimsFields` in `template_validation.go`). Rejected: rendering the whole
 context (`{{.}}`, `{{$}}`) or the whole claims map (`{{.Claims}}`), any claim not
-on the list, functions other than `get`/`default`, and `range`/`with` that do not
+on the list, functions other than `get`/`default`/`toJson`, and `range`/`with` that do not
 target a specific listed claim (e.g. `{{range .Claims}}` is rejected; `{{range
 .Claims.groups}}` is allowed).
 
@@ -592,6 +592,21 @@ Listed names apply to both direct access (`{{.Claims.employee_id}}`) and
 claim (e.g. `realm_access.roles`) are already accessible without listing them
 individually.
 
+**`toJson`** forwards an object or array claim as one JSON header:
+
+```yaml
+allowedClaims:
+  - tenant
+headers:
+  - name: "X-Tenant"
+    value: "{{get .Claims \"tenant\" | toJson}}"
+```
+
+It only serializes values the template can already reach, so the whitelist
+still applies; `{{toJson .Claims}}` is rejected. Control characters are
+JSON-escaped, and values over 8192 bytes or with bidi-override characters are
+dropped; an oversize value is logged at error level (header name only).
+
 ---
 
 ## Security Headers

hunt_20261015_regression_test.go

@@ -0,0 +1,238 @@
+package traefikoidc
+
+import (
+	"context"
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestEnhanceSessionSecurity_CaseVariantForwardedHostStaysHostScoped(t *testing.T) {
+	cases := []struct {
+		name string
+		xfh  string
+	}{
+		{name: "exact-case parent", xfh: "corp.example.com"},
+		{name: "upper-case parent", xfh: "CORP.example.com"},
+		{name: "mixed-case parent", xfh: "Corp.Example.COM"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			sm := createTestSessionManager(t)
+			t.Cleanup(func() { _ = sm.Shutdown() })
+			req := httptest.NewRequest(http.MethodGet, "https://app.corp.example.com/", nil)
+			req.Host = "app.corp.example.com"
+			req.Header.Set("X-Forwarded-Host", tc.xfh)
+			opts := sm.EnhanceSessionSecurity(nil, req)
+			if opts.Domain != "app.corp.example.com" {
+				t.Fatalf("Domain = %q, want host-scoped app.corp.example.com", opts.Domain)
+			}
+		})
+	}
+
+	t.Run("case-variant forwarded host equal to serving host is kept", func(t *testing.T) {
+		sm := createTestSessionManager(t)
+		t.Cleanup(func() { _ = sm.Shutdown() })
+		req := httptest.NewRequest(http.MethodGet, "https://internal.svc/", nil)
+		req.Host = "internal.svc"
+		req.Header.Set("X-Forwarded-Host", "App.Example.com")
+		opts := sm.EnhanceSessionSecurity(nil, req)
+		if opts.Domain != "app.example.com" {
+			t.Fatalf("Domain = %q, want app.example.com", opts.Domain)
+		}
+	})
+}
+
+func TestEnforceIatAge_RejectsFutureIat(t *testing.T) {
+	const maxAge = 24 * time.Hour
+	now := time.Now()
+	cases := []struct {
+		name    string
+		iat     time.Time
+		wantErr bool
+	}{
+		{name: "now", iat: now},
+		{name: "within future skew", iat: now.Add(ClockSkewToleranceFuture / 2)},
+		{name: "one hour ahead", iat: now.Add(time.Hour), wantErr: true},
+		{name: "just beyond skew", iat: now.Add(ClockSkewToleranceFuture + 10*time.Second), wantErr: true},
+		{name: "older than max age", iat: now.Add(-48 * time.Hour), wantErr: true},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := enforceIatAge(map[string]interface{}{"iat": float64(tc.iat.Unix())}, maxAge)
+			if (err != nil) != tc.wantErr {
+				t.Fatalf("enforceIatAge err = %v, wantErr %v", err, tc.wantErr)
+			}
+		})
+	}
+}
+
+func TestJWKCache_CooldownServesParsedEntryWithoutReparse(t *testing.T) {
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("keygen: %v", err)
+	}
+	c := NewJWKCache()
+	url := fmt.Sprintf("https://jwks.invalid/%d", time.Now().UnixNano())
+	// The raw set is empty, so only the pre-parsed entry can satisfy the lookup.
+	_ = c.cache.SetLocal(url, &JWKSet{}, time.Hour)
+	_ = c.cache.SetLocal(url+parsedKeysSuffix, &parsedJWKS{keys: map[string]crypto.PublicKey{"k1": &priv.PublicKey}}, time.Hour)
+	c.lastSignatureRefresh[url] = time.Now()
+
+	got, err := c.getPublicKeyFresh(context.Background(), url, "k1", http.DefaultClient)
+	if err != nil {
+		t.Fatalf("getPublicKeyFresh: %v", err)
+	}
+	if got != crypto.PublicKey(&priv.PublicKey) {
+		t.Fatal("cooldown branch did not serve the cached parsed key")
+	}
+}
+
+func TestFrontchannelLogout_FloodCannotEvictSignedMarkers(t *testing.T) {
+	cache := &CacheInterfaceWrapper{cache: NewUniversalCache(UniversalCacheConfig{
+		Type:             CacheTypeSession,
+		MaxSize:          5000,
+		DefaultTTL:       sessionInvalidationTTL,
+		Logger:           NewLogger("error"),
+		SkipAutoCleanup:  true,
+		MonotonicMarkers: true,
+	})}
+	oidc := &TraefikOidc{
+		logger:                   NewLogger("error"),
+		enableFrontchannelLogout: true,
+		sessionInvalidationCache: cache,
+		issuerURL:                "https://idp.example.com",
+	}
+	t.Cleanup(func() { _ = cache.cache.Close() })
+
+	if err := oidc.invalidateSession("", "real-subject"); err != nil {
+		t.Fatalf("invalidateSession: %v", err)
+	}
+	if err := oidc.checkAndMarkLogoutJTIProcessed("real-jti", time.Now().Unix()); err != nil {
+		t.Fatalf("mark jti: %v", err)
+	}
+
+	for i := 0; i < 6000; i++ {
+		req := httptest.NewRequest(http.MethodGet, fmt.Sprintf("/fc?iss=https://idp.example.com&sid=flood-%d", i), nil)
+		rw := httptest.NewRecorder()
+		oidc.handleFrontchannelLogout(rw, req)
+		if rw.Code != http.StatusOK {
+			t.Fatalf("flood request %d: status %d", i, rw.Code)
+		}
+	}
+
+	if _, ok := cache.Get(oidc.buildSessionInvalidationKey("sub", "real-subject")); !ok {
+		t.Error("backchannel sub marker evicted by front-channel flood")
+	}
+	if err := oidc.checkAndMarkLogoutJTIProcessed("real-jti", time.Now().Unix()); err == nil {
+		t.Error("jti replay marker evicted by front-channel flood: replay accepted")
+	}
+	held := 0
+	for i := 0; i < 6000; i++ {
+		if _, ok := cache.Get(oidc.buildSessionInvalidationKey("sid", fmt.Sprintf("flood-%d", i))); ok {
+			held++
+		}
+	}
+	if held > maxFrontchannelMarkers {
+		t.Errorf("front-channel markers held = %d, want <= %d", held, maxFrontchannelMarkers)
+	}
+	if _, ok := cache.Get(oidc.buildSessionInvalidationKey("sid", "flood-5999")); !ok {
+		t.Error("most recent front-channel marker must remain")
+	}
+}
+
+func TestMarkerQuota_Admit(t *testing.T) {
+	var q markerQuota
+	if got := q.admit("a", 2); got != "" {
+		t.Errorf("admit a = %q, want none", got)
+	}
+	if got := q.admit("a", 2); got != "" {
+		t.Errorf("re-admit a = %q, want none", got)
+	}
+	if got := q.admit("b", 2); got != "" {
+		t.Errorf("admit b = %q, want none", got)
+	}
+	if got := q.admit("c", 2); got != "a" {
+		t.Errorf("admit c evicted %q, want a", got)
+	}
+}
+
+func TestServeHTTP_InitWaitQueueFullFailsFast(t *testing.T) {
+	oidc := &TraefikOidc{
+		logger:                       NewLogger("error"),
+		initComplete:                 make(chan struct{}),
+		sessionManager:               createTestSessionManager(t),
+		firstRequestStarted:          1,
+		metadataRefreshStartedAtomic: 1,
+	}
+	oidc.initWaiters = maxInitWaiters
+
+	rw := httptest.NewRecorder()
+	start := time.Now()
+	oidc.ServeHTTP(rw, httptest.NewRequest(http.MethodGet, "/protected", nil))
+
+	if rw.Code != http.StatusServiceUnavailable {
+		t.Fatalf("status = %d, want 503", rw.Code)
+	}
+	if rw.Header().Get("Retry-After") == "" {
+		t.Error("missing Retry-After header")
+	}
+	if time.Since(start) > 5*time.Second {
+		t.Errorf("rejected after %v, want immediate", time.Since(start))
+	}
+	if oidc.initWaiters != maxInitWaiters {
+		t.Errorf("initWaiters = %d, want unchanged %d", oidc.initWaiters, maxInitWaiters)
+	}
+}
+
+func TestServeHTTP_InitWaiterReleasedOnCancel(t *testing.T) {
+	oidc := &TraefikOidc{
+		logger:                       NewLogger("error"),
+		initComplete:                 make(chan struct{}),
+		sessionManager:               createTestSessionManager(t),
+		firstRequestStarted:          1,
+		metadataRefreshStartedAtomic: 1,
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	req := httptest.NewRequest(http.MethodGet, "/protected", nil).WithContext(ctx)
+	oidc.ServeHTTP(httptest.NewRecorder(), req)
+	if oidc.initWaiters != 0 {
+		t.Fatalf("initWaiters = %d after canceled wait, want 0", oidc.initWaiters)
+	}
+}
+
+func TestCleanupOldCookies_CapsDeletionHeaders(t *testing.T) {
+	sm, err := NewSessionManager("test-encryption-key-32-bytes-long!!", false, "cookie.example.com", "testpref", 0, newNoOpLogger())
+	if err != nil {
+		t.Fatalf("session manager: %v", err)
+	}
+	t.Cleanup(func() { _ = sm.Shutdown() })
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.Host = "a.b.example.com"
+	for i := 0; i < 180; i++ {
+		req.AddCookie(&http.Cookie{Name: fmt.Sprintf("testpref_%d", i), Value: "x"})
+	}
+	rw := httptest.NewRecorder()
+	sm.CleanupOldCookies(rw, req)
+
+	got := len(rw.Result().Cookies())
+	if got == 0 {
+		t.Fatal("expected deletion cookies for the first wave")
+	}
+	if limit := maxCleanupCookies * 4; got > limit {
+		t.Fatalf("deletion Set-Cookie headers = %d, want <= %d", got, limit)
+	}
+	for _, c := range rw.Result().Cookies() {
+		if !strings.HasPrefix(c.Name, "testpref_") {
+			t.Errorf("unexpected deletion cookie %q", c.Name)
+		}
+	}
+}

id_token_memo_test.go

@@ -0,0 +1,50 @@
+package traefikoidc
+
+import (
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+func TestIDTokenMemoFollowsStoredToken(t *testing.T) {
+	sm, err := NewSessionManager("0123456789abcdef0123456789abcdef", false, "", "", time.Hour, NewLogger("error"))
+	if err != nil {
+		t.Fatalf("NewSessionManager: %v", err)
+	}
+	t.Cleanup(func() {
+		if err := sm.Shutdown(); err != nil {
+			t.Errorf("Shutdown: %v", err)
+		}
+	})
+	future := float64(time.Now().Add(time.Hour).Unix())
+	first := tokenWithGroups(t, map[string]interface{}{"sub": "first", "exp": future})
+	second := tokenWithGroups(t, map[string]interface{}{"sub": "second", "exp": future})
+
+	session, err := sm.GetSession(httptest.NewRequest("GET", "/", nil))
+	if err != nil {
+		t.Fatalf("GetSession: %v", err)
+	}
+	steps := []struct {
+		name  string
+		write func()
+		want  string
+	}{
+		{"first read", func() { session.SetIDToken(first) }, first},
+		{"repeat read", func() {}, first},
+		{"after overwrite", func() { session.SetIDToken(second) }, second},
+		{"after clearing", func() { session.SetIDToken("") }, ""},
+		{"after Reset", func() { session.SetIDToken(first); _ = session.GetIDToken(); session.Reset() }, ""},
+	}
+	for _, st := range steps {
+		st.write()
+		if got := session.GetIDToken(); got != st.want {
+			t.Fatalf("%s: GetIDToken = %q, want %q", st.name, got, st.want)
+		}
+		if st.name == "repeat read" && session.idTokenMemoRaw != first {
+			t.Fatal("repeat read did not go through the memo; the test no longer covers it")
+		}
+	}
+	if session.idTokenMemoRaw != "" || session.idTokenMemo != "" {
+		t.Fatal("Reset left an ID-token memo on the pooled session")
+	}
+}

internal/recovery/circuit_breaker.go

@@ -93,8 +93,16 @@ func (cb *CircuitBreaker) ExecuteWithContext(ctx context.Context, fn func() erro
 		return fmt.Errorf("circuit breaker is open")
 	}
 
-	// Execute the function
+	// A panicking fn must still settle the breaker, otherwise a half-open
+	// probe slot leaks until the next open->half-open transition.
+	panicked := true
+	defer func() {
+		if panicked {
+			cb.recordFailure()
+		}
+	}()
 	err := fn()
+	panicked = false
 
 	if err != nil {
 		cb.recordFailure()

internal/recovery/hunt_20261015_regression_test.go

@@ -0,0 +1,40 @@
+package recovery
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+)
+
+func TestCircuitBreaker_PanickingProbeReleasesHalfOpenSlot(t *testing.T) {
+	cb := NewCircuitBreaker(CircuitBreakerConfig{
+		FailureThreshold: 1,
+		SuccessThreshold: 1,
+		Timeout:          20 * time.Millisecond,
+		MaxRequests:      1,
+	}, &mockLogger{})
+
+	_ = cb.ExecuteWithContext(context.Background(), func() error { return errors.New("fail") })
+	time.Sleep(40 * time.Millisecond)
+
+	func() {
+		defer func() {
+			if recover() == nil {
+				t.Error("panic must still propagate to the caller")
+			}
+		}()
+		_ = cb.ExecuteWithContext(context.Background(), func() error { panic("boom") })
+	}()
+
+	if cb.GetState() != CircuitBreakerOpen {
+		t.Fatalf("state after panicking probe = %s, want open", cb.GetState())
+	}
+	time.Sleep(40 * time.Millisecond)
+	if err := cb.ExecuteWithContext(context.Background(), func() error { return nil }); err != nil {
+		t.Fatalf("probe after next timeout rejected: %v", err)
+	}
+	if cb.GetState() != CircuitBreakerClosed {
+		t.Fatalf("state = %s, want closed", cb.GetState())
+	}
+}

jwk.go

@@ -389,6 +389,13 @@ func (c *JWKCache) getPublicKeyFresh(ctx context.Context, jwksURL, kid string, h
 
 	if withinCooldown {
 		// Serve the cached keyset; do not fetch upstream again.
+		if v, found := c.cache.GetLocal(jwksURL + parsedKeysSuffix); found {
+			if pj, ok := v.(*parsedJWKS); ok {
+				if k, ok := pj.keys[kid]; ok {
+					return k, nil
+				}
+			}
+		}
 		if cached, found := c.cache.GetLocal(jwksURL); found {
 			if jwks, ok := cached.(*JWKSet); ok {
 				if k, ok := buildParsedJWKS(jwks).keys[kid]; ok {

logout.go

@@ -51,8 +51,43 @@ const (
 	// sessionInvalidationTTL is how long to remember invalidated sessions
 	// Should be at least as long as your session max age
 	sessionInvalidationTTL = 25 * time.Hour
+
+	// maxFrontchannelMarkers caps the sid markers the unauthenticated
+	// front-channel endpoint may keep in the shared invalidation cache, so
+	// a flood cannot LRU-evict signed backchannel and jti replay markers.
+	maxFrontchannelMarkers = 1000
 )
 
+// markerQuota is a FIFO of cache keys written on behalf of one untrusted
+// source. The zero value is ready to use.
+type markerQuota struct {
+	set  map[string]struct{}
+	keys []string
+	mu   sync.Mutex
+}
+
+// admit records key and returns the oldest key to drop once more than limit
+// keys are held, or "" when none must go. Re-admitting a held key is a no-op.
+func (q *markerQuota) admit(key string, limit int) string {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	if q.set == nil {
+		q.set = make(map[string]struct{})
+	}
+	if _, ok := q.set[key]; ok {
+		return ""
+	}
+	q.set[key] = struct{}{}
+	q.keys = append(q.keys, key)
+	if len(q.keys) <= limit {
+		return ""
+	}
+	oldest := q.keys[0]
+	q.keys = q.keys[1:]
+	delete(q.set, oldest)
+	return oldest
+}
+
 // LogoutTokenClaims represents the claims in an OIDC logout token
 // as defined in OpenID Connect Back-Channel Logout 1.0
 type LogoutTokenClaims struct {
@@ -191,6 +226,10 @@ func (t *TraefikOidc) handleFrontchannelLogout(rw http.ResponseWriter, req *http
 		return
 	}
 
+	if evicted := t.frontchannelMarkers.admit(t.buildSessionInvalidationKey("sid", sid), maxFrontchannelMarkers); evicted != "" {
+		t.sessionInvalidationCache.Delete(evicted)
+	}
+
 	t.logger.Infof("Front-channel logout: successfully invalidated session (sid=%s)", sid)
 
 	// Return a minimal HTML response that's suitable for iframe loading

main.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net/http"
@@ -85,8 +86,10 @@ var defaultExcludedURLs = map[string]struct{}{
 
 // headerTemplateFuncMap returns the function map available to custom header
 // value templates, gated by the effective claims whitelist (built-in +
-// config.AllowedClaims). It exposes exactly two helpers:
+// config.AllowedClaims). It exposes exactly three helpers:
 //   - default: substitute a fallback when a value is nil/empty.
+//   - toJson: serialize a value (e.g. an object claim) to compact JSON; nil and
+//     "" yield "" so an absent claim skips the header instead of sending `""`.
 //   - get: safe map access RESTRICTED to whitelisted claim keys, so it cannot be
 //     used to read a non-whitelisted claim, a raw token, or the whole data map
 //     (issue #149 review). This is the sole runtime enforcement of the claims
@@ -102,6 +105,16 @@ func headerTemplateFuncMap(allowedClaims map[string]bool) template.FuncMap {
 			}
 			return val
 		},
+		"toJson": func(val interface{}) (string, error) {
+			if val == nil || val == "" {
+				return "", nil
+			}
+			b, err := json.Marshal(val)
+			if err != nil {
+				return "", err
+			}
+			return string(b), nil
+		},
 		"get": func(m interface{}, key string) interface{} {
 			if !allowedClaims[key] {
 				return ""

middleware.go

@@ -158,6 +158,15 @@ func (w *optionsPreflightWriter) Write(b []byte) (int, error) {
 	return len(b), nil
 }
 
+const (
+	// maxInitWaiters bounds requests parked on initComplete so a boot-time
+	// flood with the IdP down cannot hold unbounded connections for 30s each.
+	maxInitWaiters = 512
+	// initWaitRetryAfter is the Retry-After value (seconds) sent when the
+	// init-wait queue is full.
+	initWaitRetryAfter = "5"
+)
+
 // 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.
@@ -701,6 +710,13 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	// Log waiting for initialization to help diagnose hanging requests
 	t.logger.Debug("Waiting for OIDC provider initialization...")
 
+	if atomic.AddInt32(&t.initWaiters, 1) > maxInitWaiters {
+		atomic.AddInt32(&t.initWaiters, -1)
+		rw.Header().Set("Retry-After", initWaitRetryAfter)
+		t.sendErrorResponse(rw, req, "OIDC provider initialization in progress - please try again later", http.StatusServiceUnavailable)
+		return
+	}
+
 	// time.NewTimer + Stop avoids leaking a goroutine+channel for 30s on every
 	// request when initComplete fires quickly (would happen with time.After).
 	initTimer := time.NewTimer(30 * time.Second)
@@ -708,6 +724,7 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 
 	select {
 	case <-t.initComplete:
+		atomic.AddInt32(&t.initWaiters, -1)
 		// Read issuerURL via atomic snapshot when available — replaces the
 		// metadataMu.RLock that previously fired on every non-bypass request.
 		// Under Yaegi each RLock acquisition costs 1-5ms of interpreter
@@ -744,10 +761,12 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 			return
 		}
 	case <-req.Context().Done():
+		atomic.AddInt32(&t.initWaiters, -1)
 		t.logger.Debug("Request canceled while waiting for OIDC initialization")
 		t.sendErrorResponse(rw, req, "Request canceled", http.StatusRequestTimeout)
 		return
 	case <-initTimer.C:
+		atomic.AddInt32(&t.initWaiters, -1)
 		t.logger.Error("Timeout waiting for OIDC initialization")
 		t.sendErrorResponse(rw, req, "Timeout waiting for OIDC provider initialization - please try again later", http.StatusServiceUnavailable)
 		return
@@ -1371,7 +1390,11 @@ func (t *TraefikOidc) applyHeaderTemplates(req *http.Request, p *principal) {
 		// forwarding a tainted value. Do not log the value (it commonly
 		// carries the access token); log only name + reason.
 		if reason := headerValueReason(headerValue, headerTemplateMaxLen); reason != "" {
-			t.logger.Debugf("Dropping templated header %s: value failed sanitization (%s)", headerName, reason)
+			if reason == headerReasonTooLong {
+				t.logger.Errorf("Dropping templated header %s: rendered value exceeds %d bytes", headerName, headerTemplateMaxLen)
+			} else {
+				t.logger.Debugf("Dropping templated header %s: value failed sanitization (%s)", headerName, reason)
+			}
 			continue
 		}
 		req.Header.Set(headerName, headerValue)

session.go

@@ -116,6 +116,10 @@ const (
 	defaultCookiePrefix  = "_oidc_raczylo_"
 )
 
+// maxCleanupCookies bounds the cookie names CleanupOldCookies emits deletion
+// headers for per response (up to 4 Set-Cookie headers each).
+const maxCleanupCookies = 32
+
 const (
 	// maxCookieSize is the maximum raw data size per chunk before securecookie encoding.
 	//
@@ -193,8 +197,10 @@ func compressCombinedPayload(payload *combinedSessionPayload) (string, error) {
 }
 
 // decompressCombinedPayload decompresses a base64+gzip encoded combined session payload.
+// readers pools *gzip.Reader values: a new reader allocates its 32 KB window,
+// which is a large per-request cost under yaegi.
 // Returns the deserialized payload and any error encountered.
-func decompressCombinedPayload(compressed string) (*combinedSessionPayload, error) {
+func decompressCombinedPayload(compressed string, readers *sync.Pool) (*combinedSessionPayload, error) {
 	if compressed == "" {
 		return nil, fmt.Errorf("empty compressed data")
 	}
@@ -204,11 +210,16 @@ func decompressCombinedPayload(compressed string) (*combinedSessionPayload, erro
 		return nil, fmt.Errorf("failed to decode base64: %w", err)
 	}
 
-	gr, err := gzip.NewReader(bytes.NewReader(data))
+	gr, _ := readers.Get().(*gzip.Reader)
+	if gr == nil {
+		gr, err = gzip.NewReader(bytes.NewReader(data))
+	} else {
+		err = gr.Reset(bytes.NewReader(data))
+	}
 	if err != nil {
 		return nil, fmt.Errorf("failed to create gzip reader: %w", err)
 	}
-	defer func() { _ = gr.Close() }()
+	defer readers.Put(gr)
 
 	// Limit decompressed size to prevent zip bombs
 	limitedReader := io.LimitReader(gr, 512*1024) // 512KB max
@@ -408,6 +419,7 @@ func decompressTokenInternal(compressed string) string {
 // session object reuse and supports both HTTP and HTTPS schemes.
 type SessionManager struct {
 	sessionPool    sync.Pool
+	gzipReaders    sync.Pool
 	ctx            context.Context
 	store          sessions.Store
 	logger         *Logger
@@ -929,6 +941,9 @@ func (sm *SessionManager) EnhanceSessionSecurity(options *sessions.Options, r *h
 			// service). Keep it unless it is a strict parent of the serving
 			// host, which would scope the token-bearing cookie to sibling
 			// subdomains — then fall back to the serving host.
+			// DNS names and the cookie Domain attribute are case-insensitive.
+			host = strings.ToLower(host)
+			fh = strings.ToLower(fh)
 			if !strings.HasSuffix(host, "."+fh) {
 				host = fh
 			}
@@ -1016,6 +1031,7 @@ func (sm *SessionManager) CleanupOldCookies(w http.ResponseWriter, r *http.Reque
 	}
 
 	processedCookies := make(map[string]bool)
+	deletedCookies := 0
 
 	for _, cookie := range cookies {
 		// Check if cookie belongs to this middleware instance using the configured prefix
@@ -1029,7 +1045,8 @@ func (sm *SessionManager) CleanupOldCookies(w http.ResponseWriter, r *http.Reque
 			shouldCleanup := currentDomain != "" && !sm.cleanupDone
 			sm.cleanupMutex.RUnlock()
 
-			if shouldCleanup {
+			if shouldCleanup && deletedCookies < maxCleanupCookies {
+				deletedCookies++
 				for _, domain := range domainsToClean {
 					if domain == currentDomain || domain == "."+currentDomain || "."+domain == currentDomain {
 						continue
@@ -1265,7 +1282,7 @@ func (sm *SessionManager) loadFromCombinedCookies(r *http.Request, sessionData *
 		return false
 	}
 
-	payload, err := decompressCombinedPayload(compressed)
+	payload, err := decompressCombinedPayload(compressed, &sm.gzipReaders)
 	if err != nil {
 		sm.logger.Debugf("Failed to decompress combined payload: %v", err)
 		return false
@@ -1410,6 +1427,13 @@ type SessionData struct {
 	// timed against the new owner's own writes.
 	sessionOwner atomic.Uint64
 
+	// idTokenMemoRaw and idTokenMemo cache getIDTokenUnsafe's validated result
+	// for an unchunked, uncompressed stored token, keyed by the stored value.
+	// A request reads the ID token twice, and each read re-ran full chunk
+	// validation. Cleared by Reset so no result outlives its request.
+	idTokenMemoRaw string
+	idTokenMemo    string
+
 	// cachedClaimsToken is the ID token string whose claims were last parsed and
 	// cached. A lazy, per-request cache to avoid re-parsing the JWT on every
 	// authenticated request (e.g. for headerTemplates). Protected by sessionMutex.
@@ -2086,6 +2110,8 @@ func (sd *SessionData) Reset() {
 	sd.cachedClaimsToken = ""
 	sd.cachedClaims = nil
 	sd.cachedClaimsErr = nil
+	sd.idTokenMemoRaw = ""
+	sd.idTokenMemo = ""
 
 	// Reset the refresh mutex to ensure clean state
 	// Note: We don't need to lock it since sessionMutex is already held
@@ -3017,6 +3043,11 @@ func (sd *SessionData) getIDTokenUnsafe() string {
 		return token
 	}
 
+	memoable := token != "" && !compressed && len(sd.idTokenChunks) == 0
+	if memoable && token == sd.idTokenMemoRaw {
+		return sd.idTokenMemo
+	}
+
 	result := sd.manager.chunkManager.GetToken(
 		token,
 		compressed,
@@ -3024,11 +3055,14 @@ func (sd *SessionData) getIDTokenUnsafe() string {
 		IDTokenConfig,
 	)
 
+	validated := result.Token
 	if result.Error != nil {
-		return ""
+		validated = ""
 	}
-
-	return result.Token
+	if memoable {
+		sd.idTokenMemoRaw, sd.idTokenMemo = token, validated
+	}
+	return validated
 }
 
 // getRefreshTokenUnsafe retrieves the refresh token without acquiring locks.

session_chunk_manager.go

@@ -10,6 +10,7 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+	"unicode/utf8"
 
 	"github.com/gorilla/sessions"
 	"github.com/lukaszraczylo/traefikoidc/internal/pool"
@@ -89,9 +90,14 @@ type TokenRetrievalResult struct {
 // and error handling to ensure data integrity and prevent security vulnerabilities
 // throughout the process.
 type ChunkManager struct {
-	lastCleanup    time.Time
-	ctx            context.Context
-	mutex          *sync.RWMutex
+	lastCleanup time.Time
+	ctx         context.Context
+	mutex       *sync.RWMutex
+	// contentValid holds keys of tokens that passed every content-only check.
+	// Browsers resend the same cookie, and re-running those checks on every
+	// request dominated per-request cost under yaegi. Guarded by contentMu.
+	contentValid   map[string]tokenTimes
+	contentMu      sync.Mutex
 	cancel         context.CancelFunc
 	sessionMap     map[string]*SessionEntry
 	logger         *Logger
@@ -127,14 +133,15 @@ func NewChunkManager(logger *Logger) *ChunkManager {
 	ctx, cancel := context.WithCancel(context.Background())
 
 	cm := &ChunkManager{
-		logger:      logger,
-		mutex:       &sync.RWMutex{},
-		ctx:         ctx,
-		cancel:      cancel,
-		sessionMap:  make(map[string]*SessionEntry),
-		maxSessions: 200,              // CRITICAL FIX: Reduced from 1000 to 200 per instance
-		sessionTTL:  15 * time.Minute, // CRITICAL FIX: Reduced from 24h to 15 minutes
-		lastCleanup: time.Now(),
+		logger:       logger,
+		mutex:        &sync.RWMutex{},
+		ctx:          ctx,
+		cancel:       cancel,
+		sessionMap:   make(map[string]*SessionEntry),
+		contentValid: make(map[string]tokenTimes),
+		maxSessions:  200,              // CRITICAL FIX: Reduced from 1000 to 200 per instance
+		sessionTTL:   15 * time.Minute, // CRITICAL FIX: Reduced from 24h to 15 minutes
+		lastCleanup:  time.Now(),
 	}
 
 	// Start background cleanup routine
@@ -293,26 +300,38 @@ func (cm *ChunkManager) processSingleToken(token string, compressed bool, config
 // Returns:
 //   - TokenRetrievalResult with the validated token or validation error.
 func (cm *ChunkManager) validateToken(token string, config TokenConfig) TokenRetrievalResult {
-	if sizeErr := cm.validateTokenSize(token, config); sizeErr != nil {
-		return TokenRetrievalResult{Token: "", Error: sizeErr}
+	// Content-only checks depend on the token string alone, so a token that
+	// passed them once skips them. Expiry and freshness always run.
+	key := contentValidKey(token, config)
+	times, cached := cm.cachedTokenTimes(key)
+
+	if !cached {
+		if sizeErr := cm.validateTokenSize(token, config); sizeErr != nil {
+			return TokenRetrievalResult{Token: "", Error: sizeErr}
+		}
+
+		cm.validateChunkingEfficiency(token, config)
+
+		if contentErr := cm.validateTokenContent(token, config); contentErr != nil {
+			return TokenRetrievalResult{Token: "", Error: contentErr}
+		}
+		times = cm.tokenTimesOf(token)
 	}
 
-	cm.validateChunkingEfficiency(token, config)
-
-	if contentErr := cm.validateTokenContent(token, config); contentErr != nil {
-		return TokenRetrievalResult{Token: "", Error: contentErr}
-	}
-
-	if expErr := cm.validateTokenExpiration(token, config); expErr != nil {
+	if expErr := cm.validateTokenExpiration(times, config); expErr != nil {
 		return TokenRetrievalResult{Token: "", Error: expErr}
 	}
 
-	if freshnessErr := cm.validateTokenFreshness(token, config); freshnessErr != nil {
+	if freshnessErr := cm.validateTokenFreshness(times, config); freshnessErr != nil {
 		return TokenRetrievalResult{Token: "", Error: freshnessErr}
 	}
 
 	// Determine if token is opaque or JWT based on format
 	// JWT tokens have exactly 2 dots (3 parts: header.payload.signature)
+	if cached {
+		return TokenRetrievalResult{Token: token, Error: nil}
+	}
+
 	dotCount := strings.Count(token, ".")
 	isJWT := dotCount == 2
 
@@ -338,6 +357,7 @@ func (cm *ChunkManager) validateToken(token string, config TokenConfig) TokenRet
 		}
 	}
 
+	cm.markContentValid(key, times)
 	return TokenRetrievalResult{Token: token, Error: nil}
 }
 
@@ -350,6 +370,53 @@ func (cm *ChunkManager) validateToken(token string, config TokenConfig) TokenRet
 //
 // Returns:
 //   - TokenRetrievalResult with the reassembled token or error.
+//
+// tokenTimes holds a token's parsed exp and iat claims. They are part of the
+// token content, so a content-cache entry keeps them to avoid re-parsing the
+// payload on every request. The checks that use them still run each time.
+type tokenTimes struct {
+	exp, iat       *time.Time
+	expErr, iatErr error
+	jwt            bool
+}
+
+// tokenTimesOf parses exp and iat from a JWT-shaped token.
+func (cm *ChunkManager) tokenTimesOf(token string) tokenTimes {
+	if !strings.Contains(token, ".") {
+		return tokenTimes{}
+	}
+	t := tokenTimes{jwt: true}
+	t.exp, t.expErr = cm.extractJWTExpiration(token)
+	t.iat, t.iatErr = cm.extractJWTIssuedAt(token)
+	return t
+}
+
+// contentValidCacheMax bounds contentValid; the map is cleared when full.
+const contentValidCacheMax = 4096
+
+// contentValidKey keys a token by type and SHA-256 so the cache does not
+// retain token values.
+func contentValidKey(token string, config TokenConfig) string {
+	sum := sha256.Sum256([]byte(token))
+	return config.Type + ":" + string(sum[:])
+}
+
+func (cm *ChunkManager) cachedTokenTimes(key string) (tokenTimes, bool) {
+	cm.contentMu.Lock()
+	t, ok := cm.contentValid[key]
+	cm.contentMu.Unlock()
+	return t, ok
+}
+
+func (cm *ChunkManager) markContentValid(key string, t tokenTimes) {
+	cm.contentMu.Lock()
+	if len(cm.contentValid) >= contentValidCacheMax {
+		cm.contentValid = make(map[string]tokenTimes)
+	}
+	cm.contentValid[key] = t
+	cm.contentMu.Unlock()
+}
+
 func (cm *ChunkManager) processChunkedToken(chunks map[int]*sessions.Session, config TokenConfig) TokenRetrievalResult {
 	if len(chunks) > config.MaxChunks {
 		err := fmt.Errorf("too many %s token chunks (%d, max: %d)", config.Type, len(chunks), config.MaxChunks)
@@ -504,7 +571,9 @@ func (cm *ChunkManager) validateJWTFormat(token string, tokenType string) error
 			return err
 		}
 
-		for _, char := range part {
+		// Byte loop: a multi-byte rune fails on its first byte either way.
+		for j := 0; j < len(part); j++ {
+			char := part[j]
 			if !((char >= 'A' && char <= 'Z') ||
 				(char >= 'a' && char <= 'z') ||
 				(char >= '0' && char <= '9') ||
@@ -717,9 +786,10 @@ func (cm *ChunkManager) validateTokenSanitization(token string, config TokenConf
 		return err
 	}
 
-	// Check for control characters (ASCII 0-31 and 127)
-	for i, char := range token {
-		if char < 32 || char == 127 {
+	// Check for control characters (ASCII 0-31 and 127). Byte loop: bytes of
+	// a multi-byte rune are >= 0x80, and i is a byte offset either way.
+	for i := 0; i < len(token); i++ {
+		if char := token[i]; char < 32 || char == 127 {
 			err := fmt.Errorf("%s token contains control character at position %d", config.Type, i)
 			return err
 		}
@@ -921,7 +991,13 @@ func (cm *ChunkManager) detectRepeatedCharacters(token string, config TokenConfi
 	currentRepeated := 1
 	var lastChar rune
 
-	for i, char := range token {
+	// Index loops, not range: under yaegi, ranging over a string allocates
+	// O(n²) bytes, which dominated per-request cost for 1-2 KB tokens.
+	for i := 0; i < len(token); {
+		char, size := rune(token[i]), 1
+		if char >= utf8.RuneSelf {
+			char, size = utf8.DecodeRuneInString(token[i:])
+		}
 		if i > 0 && char == lastChar {
 			currentRepeated++
 			if currentRepeated > maxRepeated {
@@ -931,6 +1007,7 @@ func (cm *ChunkManager) detectRepeatedCharacters(token string, config TokenConfi
 			currentRepeated = 1
 		}
 		lastChar = char
+		i += size
 	}
 
 	threshold := 20
@@ -941,8 +1018,13 @@ func (cm *ChunkManager) detectRepeatedCharacters(token string, config TokenConfi
 	}
 
 	charFreq := make(map[rune]int)
-	for _, char := range token {
+	for i := 0; i < len(token); {
+		char, size := rune(token[i]), 1
+		if char >= utf8.RuneSelf {
+			char, size = utf8.DecodeRuneInString(token[i:])
+		}
 		charFreq[char]++
+		i += size
 	}
 
 	tokenLen := len(token)
@@ -963,21 +1045,21 @@ func (cm *ChunkManager) detectRepeatedCharacters(token string, config TokenConfi
 // It extracts and checks JWT expiration claims to ensure tokens are not expired
 // and detects tokens with suspicious expiration times.
 // Parameters:
-//   - token: The token to check expiration for.
+//   - times: The token's parsed claims (see tokenTimesOf).
 //   - config: Token configuration for error context.
 //
 // Returns:
 //   - An error if the token is expired or has invalid expiration, nil if valid.
 //
 //nolint:unparam // error return kept for API consistency and future use
-func (cm *ChunkManager) validateTokenExpiration(token string, config TokenConfig) error {
-	if !strings.Contains(token, ".") {
+func (cm *ChunkManager) validateTokenExpiration(times tokenTimes, config TokenConfig) error {
+	if !times.jwt {
 		return nil
 	}
 
-	expiration, err := cm.extractJWTExpiration(token)
-	if err != nil {
-		cm.logger.Debugf("Could not extract expiration from %s token: %v", config.Type, err)
+	expiration := times.exp
+	if times.expErr != nil {
+		cm.logger.Debugf("Could not extract expiration from %s token: %v", config.Type, times.expErr)
 		return nil
 	}
 
@@ -1062,19 +1144,19 @@ func (cm *ChunkManager) extractJWTExpiration(token string) (*time.Time, error) {
 // It examines the 'iat' (issued at) claim to detect tokens issued too far
 // in the future or suspiciously old tokens that might indicate replay attacks.
 // Parameters:
-//   - token: The token to check freshness for.
+//   - times: The token's parsed claims (see tokenTimesOf).
 //   - config: Token configuration for error context.
 //
 // Returns:
 //   - An error if the token freshness is suspicious, nil if acceptable.
-func (cm *ChunkManager) validateTokenFreshness(token string, config TokenConfig) error {
-	if !strings.Contains(token, ".") {
+func (cm *ChunkManager) validateTokenFreshness(times tokenTimes, config TokenConfig) error {
+	if !times.jwt {
 		return nil
 	}
 
-	issuedAt, err := cm.extractJWTIssuedAt(token)
-	if err != nil {
-		cm.logger.Debugf("Could not extract issued time from %s token: %v", config.Type, err)
+	issuedAt := times.iat
+	if times.iatErr != nil {
+		cm.logger.Debugf("Could not extract issued time from %s token: %v", config.Type, times.iatErr)
 		return nil
 	}
 

template_validation.go

@@ -22,6 +22,7 @@ var allowedRootTokenFields = map[string]bool{
 var validateTemplateParseFuncs = map[string]any{
 	"get":     struct{}{},
 	"default": struct{}{},
+	"toJson":  struct{}{},
 }
 
 // claimsWhitelist returns the effective set of claim field names a header
@@ -183,12 +184,14 @@ func (v *templateValidator) validateCommand(cmd *parse.CommandNode, dotIsRoot bo
 	return nil
 }
 
-// validateFunctionCall allows only get/default. get's map argument must be a
+// validateFunctionCall allows only get/default/toJson. get's map argument must be a
 // claims reference (never the root) and default's arguments are validated as
 // values; the runtime get additionally enforces the key whitelist.
 func (v *templateValidator) validateFunctionCall(name string, args []parse.Node, dotIsRoot bool) error {
 	switch name {
-	case "default":
+	case "default", "toJson":
+		// toJson only serializes what its (validated) arguments or piped input
+		// already expose; it cannot reach anything a direct reference could not.
 		for _, arg := range args {
 			if err := v.validateValue(arg, dotIsRoot); err != nil {
 				return err

tojson_template_test.go

@@ -0,0 +1,286 @@
+package traefikoidc
+
+import (
+	"encoding/json"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"text/template"
+)
+
+// renderHeaderTemplate runs tmplStr through the same validator, funcMap and
+// applyHeaderTemplates path production uses. validateErr is the static-validation
+// error; got is the forwarded header value ("" when absent or dropped).
+func renderHeaderTemplate(t *testing.T, tmplStr string, extraClaims []string, claims map[string]interface{}) (got string, validateErr error) {
+	t.Helper()
+	allowed := claimsWhitelist(extraClaims)
+	if err := validateTemplateSecure(tmplStr, allowed); err != nil {
+		return "", err
+	}
+	tmpl, err := template.New("X-Test").Funcs(headerTemplateFuncMap(allowed)).Option("missingkey=zero").Parse(tmplStr)
+	if err != nil {
+		t.Fatalf("validated template failed to parse: %v", err)
+	}
+	o := &TraefikOidc{logger: NewLogger("error"), headerTemplates: map[string]*template.Template{"X-Test": tmpl}}
+	req := httptest.NewRequest("GET", "/", nil)
+	o.applyHeaderTemplates(req, &principal{Claims: claims, AccessToken: "AT-SECRET", IDToken: "IDT-SECRET", RefreshToken: "RT-SECRET"})
+	return req.Header.Get("X-Test"), nil
+}
+
+func TestToJson_ObjectClaimRoundTrips(t *testing.T) {
+	claims := map[string]interface{}{
+		"tenant": map[string]interface{}{"id": "t-1", "plan": "pro", "flags": []interface{}{"a", "b"}, "n": 3.0, "ok": true, "nil": nil},
+	}
+	for _, tmpl := range []string{
+		`{{ get .Claims "tenant" | toJson }}`,
+		`{{ toJson (get .Claims "tenant") }}`,
+		`{{ toJson .Claims.tenant }}`,
+		`{{ with .Claims.tenant }}{{ toJson . }}{{ end }}`,
+		`{{ $t := .Claims.tenant }}{{ toJson $t }}`,
+		`{{ toJson $.Claims.tenant }}`,
+	} {
+		got, err := renderHeaderTemplate(t, tmpl, []string{"tenant"}, claims)
+		if err != nil {
+			t.Fatalf("%s: unexpected validation error: %v", tmpl, err)
+		}
+		var back map[string]interface{}
+		if err := json.Unmarshal([]byte(got), &back); err != nil {
+			t.Fatalf("%s: output %q is not valid JSON: %v", tmpl, got, err)
+		}
+		if back["id"] != "t-1" || back["plan"] != "pro" || back["n"] != 3.0 || back["ok"] != true {
+			t.Fatalf("%s: round trip mismatch: %q", tmpl, got)
+		}
+	}
+}
+
+func TestToJson_ValueTypes(t *testing.T) {
+	claims := map[string]interface{}{
+		"groups": []interface{}{"admin", "users"},
+		"email":  "[email protected]",
+		"exp":    1700000000.0,
+		"role":   "",
+	}
+	cases := []struct{ name, tmpl, want string }{
+		{"array", `{{ toJson .Claims.groups }}`, `["admin","users"]`},
+		{"string", `{{ toJson .Claims.email }}`, `"[email protected]"`},
+		{"number", `{{ toJson .Claims.exp }}`, `1700000000`},
+		{"missing claim skips header", `{{ toJson .Claims.department }}`, ``},
+		{"missing via get skips header", `{{ get .Claims "department" | toJson }}`, ``},
+		{"empty string skips header", `{{ toJson .Claims.role }}`, ``},
+		{"literal string", `{{ toJson "x" }}`, `"x"`},
+		{"literal number", `{{ toJson 5 }}`, `5`},
+		{"composes with surrounding text", `v={{ toJson .Claims.groups }};`, `v=["admin","users"];`},
+	}
+	for _, c := range cases {
+		got, err := renderHeaderTemplate(t, c.tmpl, nil, claims)
+		if err != nil {
+			t.Fatalf("%s: unexpected validation error: %v", c.name, err)
+		}
+		if got != c.want {
+			t.Errorf("%s: got %q want %q", c.name, got, c.want)
+		}
+	}
+}
+
+func TestToJson_EmptyAndNilContainers(t *testing.T) {
+	claims := map[string]interface{}{
+		"realm_access": map[string]interface{}{},
+		"groups":       []interface{}{},
+	}
+	if got, _ := renderHeaderTemplate(t, `{{ toJson .Claims.realm_access }}`, nil, claims); got != `{}` {
+		t.Errorf("empty object: got %q", got)
+	}
+	if got, _ := renderHeaderTemplate(t, `{{ toJson .Claims.groups }}`, nil, claims); got != `[]` {
+		t.Errorf("empty array: got %q", got)
+	}
+	if got, _ := renderHeaderTemplate(t, `{{ toJson .Claims.groups }}`, nil, nil); got != `` {
+		t.Errorf("nil claims: got %q", got)
+	}
+}
+
+func TestToJson_UnmarshalableValueDropsHeader(t *testing.T) {
+	fn := headerTemplateFuncMap(nil)["toJson"].(func(interface{}) (string, error))
+	if _, err := fn(make(chan int)); err == nil {
+		t.Fatal("expected error for unmarshalable value")
+	}
+	// A non-finite float is the only way a claim map could carry one in.
+	if _, err := fn(map[string]interface{}{"x": func() {}}); err == nil {
+		t.Fatal("expected error for func value")
+	}
+}
+
+// Security: toJson must not widen what a template can reach.
+func TestToJson_SecurityBoundary(t *testing.T) {
+	claims := map[string]interface{}{
+		"email":  "[email protected]",
+		"secret": "NOT-WHITELISTED",
+		"tenant": map[string]interface{}{"id": "t"},
+	}
+	rejected := []string{
+		`{{ toJson . }}`,
+		`{{ toJson $ }}`,
+		`{{ toJson .Claims }}`,
+		`{{ toJson $.Claims }}`,
+		`{{ .Claims | toJson }}`,
+		`{{ toJson .Claims.secret }}`,
+		`{{ toJson $.Claims.secret }}`,
+		`{{ toJson .AccessToken }}{{ toJson .Claims }}`,
+		`{{ get .Claims "secret" | toJson }}`,
+		`{{ toJson (get . "AccessToken") }}`,
+		`{{ get . "Claims" | toJson }}`,
+		`{{ with .Claims }}{{ toJson . }}{{ end }}`,
+		`{{ range .Claims }}{{ toJson . }}{{ end }}`,
+		`{{ toJson (index .Claims "secret") }}`,
+		`{{ toJson (printf "%v" .Claims) }}`,
+		`{{ toJson (call .Claims) }}`,
+		`{{ tojson .Claims.email }}`,
+		`{{ toJSON .Claims.email }}`,
+		`{{ toJson | js }}`,
+	}
+	for _, tmpl := range rejected {
+		if got, err := renderHeaderTemplate(t, tmpl, nil, claims); err == nil {
+			t.Errorf("%s: must be rejected by validation, rendered %q", tmpl, got)
+		}
+	}
+
+	// Dynamic key: static validation cannot see it, the runtime whitelist must.
+	dyn := `{{ get .Claims .Claims.email | toJson }}`
+	if got, err := renderHeaderTemplate(t, dyn, nil, map[string]interface{}{"email": "secret", "secret": "LEAK"}); err != nil || strings.Contains(got, "LEAK") {
+		t.Errorf("dynamic key leaked a non-whitelisted claim: err=%v got=%q", err, got)
+	}
+}
+
+// Security: tokens and the claims map never appear in output, even from a
+// validated template that serializes a whitelisted claim.
+func TestToJson_NoTokenLeak(t *testing.T) {
+	claims := map[string]interface{}{"tenant": map[string]interface{}{"id": "t"}}
+	got, err := renderHeaderTemplate(t, `{{ toJson .Claims.tenant }}`, []string{"tenant"}, claims)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, s := range []string{"AT-SECRET", "IDT-SECRET", "RT-SECRET"} {
+		if strings.Contains(got, s) {
+			t.Fatalf("token %s leaked into %q", s, got)
+		}
+	}
+}
+
+// Security: a non-whitelisted claim stays unreachable until the operator opts
+// in via allowedClaims, with or without toJson.
+func TestToJson_RequiresAllowedClaims(t *testing.T) {
+	claims := map[string]interface{}{"tenant": map[string]interface{}{"id": "t"}}
+	if _, err := renderHeaderTemplate(t, `{{ toJson .Claims.tenant }}`, nil, claims); err == nil {
+		t.Error("direct reference to non-whitelisted claim must be rejected")
+	}
+	got, err := renderHeaderTemplate(t, `{{ get .Claims "tenant" | toJson }}`, nil, claims)
+	if err == nil {
+		t.Errorf("literal get key outside whitelist must be rejected, rendered %q", got)
+	}
+}
+
+// Security: hostile claim content must not produce header injection.
+func TestToJson_HeaderInjectionHardening(t *testing.T) {
+	cases := []struct {
+		name  string
+		value interface{}
+		// forwarded reports whether the header is expected to reach upstream.
+		forwarded bool
+	}{
+		{"CRLF is escaped to \\r\\n", map[string]interface{}{"x": "a\r\nX-Evil: 1"}, true},
+		{"NUL and control chars escaped", map[string]interface{}{"x": "a\x00\x07b"}, true},
+		{"LS/PS escaped", map[string]interface{}{"x": "a

b"}, true},
+		{"HTML chars escaped", map[string]interface{}{"x": "<script>&"}, true},
+		{"quote and backslash escaped", map[string]interface{}{"x": `"\`}, true},
+		{"bidi override dropped by sanitizer", map[string]interface{}{"x": "a\u202Eb"}, false},
+		{"bidi isolate dropped by sanitizer", map[string]interface{}{"x": "a\u2066b"}, false},
+		{"oversize dropped by sanitizer", map[string]interface{}{"x": strings.Repeat("A", headerTemplateMaxLen)}, false},
+	}
+	for _, c := range cases {
+		got, err := renderHeaderTemplate(t, `{{ toJson .Claims.realm_access }}`, nil, map[string]interface{}{"realm_access": c.value})
+		if err != nil {
+			t.Fatalf("%s: %v", c.name, err)
+		}
+		if !c.forwarded {
+			if got != "" {
+				t.Errorf("%s: tainted value must be dropped, got %d bytes", c.name, len(got))
+			}
+			continue
+		}
+		if got == "" {
+			t.Errorf("%s: safe escaped JSON must be forwarded", c.name)
+			continue
+		}
+		for _, r := range got {
+			if r < 0x20 || r == 0x7f || r == 0x2028 || r == 0x2029 {
+				t.Errorf("%s: raw control rune %U in %q", c.name, r, got)
+			}
+		}
+		if strings.ContainsAny(got, "<>&") {
+			t.Errorf("%s: unescaped HTML char in %q", c.name, got)
+		}
+		var back map[string]interface{}
+		if err := json.Unmarshal([]byte(got), &back); err != nil {
+			t.Errorf("%s: not valid JSON: %v", c.name, err)
+		}
+	}
+}
+
+// Default-preserving: existing templates are unaffected and toJson is not
+// available to anything but validated header templates.
+func TestToJson_ExistingTemplatesUnchanged(t *testing.T) {
+	claims := map[string]interface{}{"email": "[email protected]", "groups": []interface{}{"x", "y"}}
+	got, err := renderHeaderTemplate(t, `{{ .Claims.email }}|{{range $i, $e := .Claims.groups}}{{if $i}},{{end}}{{$e}}{{end}}|{{ default "d" .Claims.role }}`, nil, claims)
+	if err != nil || got != "[email protected]|x,y|d" {
+		t.Fatalf("got %q err=%v", got, err)
+	}
+	if _, ok := headerTemplateFuncMap(nil)["toJson"]; !ok {
+		t.Fatal("toJson missing from func map")
+	}
+	for _, name := range []string{"env", "expandenv", "printf", "call", "index", "js"} {
+		if _, ok := headerTemplateFuncMap(nil)[name]; ok {
+			t.Errorf("%s must not be exposed", name)
+		}
+	}
+}
+
+func TestToJson_ConfigValidate(t *testing.T) {
+	cfg := issue149BaseConfig()
+	cfg.AllowedClaims = []string{"tenant"}
+	cfg.Headers = []TemplatedHeader{{Name: "X-Tenant", Value: `{{ get .Claims "tenant" | toJson }}`}}
+	if err := cfg.Validate(); err != nil {
+		t.Fatalf("toJson header must validate: %v", err)
+	}
+	cfg.Headers = []TemplatedHeader{{Name: "X-All", Value: `{{ toJson .Claims }}`}}
+	if err := cfg.Validate(); err == nil {
+		t.Fatal("toJson of whole Claims must fail validation")
+	}
+}
+
+// Oversize output is operator-actionable, so it logs at error level (name and
+// size limit only, never the value); other sanitizer drops stay at debug.
+func TestToJson_OversizeLogsError(t *testing.T) {
+	run := func(claim map[string]interface{}) string {
+		var buf strings.Builder
+		logger := NewLogger("debug")
+		logger.logError.SetOutput(&buf)
+		tmpl := template.Must(template.New("X-Test").Funcs(headerTemplateFuncMap(nil)).Parse(`{{ toJson .Claims.realm_access }}`))
+		o := &TraefikOidc{logger: logger, headerTemplates: map[string]*template.Template{"X-Test": tmpl}}
+		req := httptest.NewRequest("GET", "/", nil)
+		o.applyHeaderTemplates(req, &principal{Claims: map[string]interface{}{"realm_access": claim}})
+		if req.Header.Get("X-Test") != "" {
+			t.Fatal("tainted header must be dropped")
+		}
+		return buf.String()
+	}
+	big := strings.Repeat("S3CRET", headerTemplateMaxLen)
+	out := run(map[string]interface{}{"x": big})
+	if !strings.Contains(out, "X-Test") || !strings.Contains(out, "exceeds") {
+		t.Errorf("oversize must log an error naming the header, got %q", out)
+	}
+	if strings.Contains(out, "S3CRET") {
+		t.Error("error log must not contain the value")
+	}
+	if out := run(map[string]interface{}{"x": "a\u202Eb"}); out != "" {
+		t.Errorf("non-length sanitizer drop must not log at error level, got %q", out)
+	}
+}

types.go

@@ -111,6 +111,9 @@ type TraefikOidc struct {
 	// recovery attempt. Stored atomically so the hot ServeHTTP path can
 	// throttle retries without acquiring metadataRetryMutex on every request.
 	lastMetadataRetryNano int64
+	// initWaiters counts requests parked on initComplete; bounded by
+	// maxInitWaiters so a boot-time flood cannot hold unbounded connections.
+	initWaiters int32
 	// firstRequestStarted is 0 until the very first non-health request fires
 	// the background-task bootstrap; then it flips to 1 via CAS. Replaces the
 	// firstRequestMutex + firstRequestReceived combo which previously took
@@ -224,6 +227,7 @@ type TraefikOidc struct {
 	dcrMu                     sync.Mutex
 	shutdownOnce              sync.Once
 	sessionInvalidationCache  CacheInterface
+	frontchannelMarkers       markerQuota
 	refreshResultCache        CacheInterface
 	minimalHeaders            bool
 	stripAuthCookies          bool