diff --git a/main_servehttp_test.go b/main_servehttp_test.go
index cf4cace..3ca87d1 100644
--- a/main_servehttp_test.go
+++ b/main_servehttp_test.go
@@ -79,34 +79,186 @@ func TestServeHTTP_ExcludedURLs(t *testing.T) {
 	}
 }
 
-// TestServeHTTP_EventStream tests the event-stream bypass functionality
+// TestServeHTTP_EventStream tests the event-stream (SSE) bypass: the
+// handshake must skip the OIDC redirect dance (clients can't follow it
+// mid-stream) but it must STILL require an authenticated session, otherwise
+// any caller could reach the backend by setting Accept: text/event-stream.
 func TestServeHTTP_EventStream(t *testing.T) {
-	nextCalled := false
-	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		nextCalled = true
-		w.WriteHeader(http.StatusOK)
+	sessionManager := createTestSessionManager(t)
+
+	newOidc := func(next http.Handler) *TraefikOidc {
+		oidc := &TraefikOidc{
+			next:                   next,
+			logger:                 NewLogger("debug"),
+			initComplete:           make(chan struct{}),
+			sessionManager:         sessionManager,
+			firstRequestReceived:   true,
+			metadataRefreshStarted: true,
+			issuerURL:              "https://provider.example.com",
+		}
+		close(oidc.initComplete)
+		return oidc
+	}
+
+	t.Run("unauthenticated_request_is_rejected", func(t *testing.T) {
+		nextCalled := false
+		oidc := newOidc(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			nextCalled = true
+			w.WriteHeader(http.StatusOK)
+		}))
+
+		req := httptest.NewRequest("GET", "/events", nil)
+		req.Header.Set("Accept", "text/event-stream")
+		rw := httptest.NewRecorder()
+
+		oidc.ServeHTTP(rw, req)
+
+		if rw.Code != http.StatusUnauthorized {
+			t.Errorf("expected 401 for unauthenticated SSE request, got %d", rw.Code)
+		}
+		if nextCalled {
+			t.Error("backend handler must NOT be called for unauthenticated SSE bypass")
+		}
 	})
 
-	oidc := &TraefikOidc{
-		next:                   next,
-		logger:                 NewLogger("debug"),
-		initComplete:           make(chan struct{}),
-		sessionManager:         createTestSessionManager(t),
-		firstRequestReceived:   true,
-		metadataRefreshStarted: true,
-		issuerURL:              "https://provider.example.com",
+	t.Run("authenticated_request_bypasses_to_backend", func(t *testing.T) {
+		nextCalled := false
+		var forwardedUser string
+		oidc := newOidc(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			nextCalled = true
+			forwardedUser = r.Header.Get("X-Forwarded-User")
+			w.WriteHeader(http.StatusOK)
+		}))
+
+		req := httptest.NewRequest("GET", "/events", nil)
+		req.Header.Set("Accept", "text/event-stream")
+
+		// Build an authenticated session and inject its cookies onto req.
+		session, err := sessionManager.GetSession(req)
+		if err != nil {
+			t.Fatalf("failed to create test session: %v", err)
+		}
+		session.SetEmail("user@example.com")
+		if err := session.SetAuthenticated(true); err != nil {
+			t.Fatalf("failed to mark session authenticated: %v", err)
+		}
+		setupRW := httptest.NewRecorder()
+		if err := session.Save(req, setupRW); err != nil {
+			t.Fatalf("failed to save session: %v", err)
+		}
+		for _, c := range setupRW.Result().Cookies() {
+			req.AddCookie(c)
+		}
+
+		rw := httptest.NewRecorder()
+		oidc.ServeHTTP(rw, req)
+
+		if !nextCalled {
+			t.Fatal("expected authenticated SSE request to be forwarded to backend")
+		}
+		if forwardedUser != "user@example.com" {
+			t.Errorf("expected X-Forwarded-User=user@example.com, got %q", forwardedUser)
+		}
+	})
+}
+
+// TestServeHTTP_WebSocketUpgrade mirrors the SSE behavior: WebSocket
+// handshake bypasses the OIDC redirect (clients can't follow it) but the
+// session must already be authenticated, otherwise the backend is exposed
+// to any caller setting `Connection: Upgrade` + `Upgrade: websocket`.
+func TestServeHTTP_WebSocketUpgrade(t *testing.T) {
+	sessionManager := createTestSessionManager(t)
+
+	newOidc := func(next http.Handler) *TraefikOidc {
+		oidc := &TraefikOidc{
+			next:                   next,
+			logger:                 NewLogger("debug"),
+			initComplete:           make(chan struct{}),
+			sessionManager:         sessionManager,
+			firstRequestReceived:   true,
+			metadataRefreshStarted: true,
+			issuerURL:              "https://provider.example.com",
+		}
+		close(oidc.initComplete)
+		return oidc
 	}
-	close(oidc.initComplete)
 
-	req := httptest.NewRequest("GET", "/events", nil)
-	req.Header.Set("Accept", "text/event-stream")
-	rw := httptest.NewRecorder()
+	t.Run("unauthenticated_upgrade_is_rejected", func(t *testing.T) {
+		nextCalled := false
+		oidc := newOidc(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			nextCalled = true
+		}))
 
-	oidc.ServeHTTP(rw, req)
+		req := httptest.NewRequest("GET", "/ws", nil)
+		req.Header.Set("Connection", "Upgrade")
+		req.Header.Set("Upgrade", "websocket")
+		rw := httptest.NewRecorder()
 
-	if !nextCalled {
-		t.Error("expected event-stream request to bypass OIDC")
-	}
+		oidc.ServeHTTP(rw, req)
+
+		if rw.Code != http.StatusUnauthorized {
+			t.Errorf("expected 401 for unauthenticated WS upgrade, got %d", rw.Code)
+		}
+		if nextCalled {
+			t.Error("backend handler must NOT be called for unauthenticated WS bypass")
+		}
+	})
+
+	t.Run("authenticated_upgrade_bypasses_to_backend", func(t *testing.T) {
+		nextCalled := false
+		var forwardedUser string
+		oidc := newOidc(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			nextCalled = true
+			forwardedUser = r.Header.Get("X-Forwarded-User")
+		}))
+
+		req := httptest.NewRequest("GET", "/ws", nil)
+		// Mixed-case + multi-token Connection header to exercise parsing.
+		req.Header.Set("Connection", "keep-alive, Upgrade")
+		req.Header.Set("Upgrade", "WebSocket")
+
+		session, err := sessionManager.GetSession(req)
+		if err != nil {
+			t.Fatalf("failed to create test session: %v", err)
+		}
+		session.SetEmail("ws-user@example.com")
+		if err := session.SetAuthenticated(true); err != nil {
+			t.Fatalf("failed to mark session authenticated: %v", err)
+		}
+		setupRW := httptest.NewRecorder()
+		if err := session.Save(req, setupRW); err != nil {
+			t.Fatalf("failed to save session: %v", err)
+		}
+		for _, c := range setupRW.Result().Cookies() {
+			req.AddCookie(c)
+		}
+
+		rw := httptest.NewRecorder()
+		oidc.ServeHTTP(rw, req)
+
+		if !nextCalled {
+			t.Fatal("expected authenticated WS handshake to be forwarded to backend")
+		}
+		if forwardedUser != "ws-user@example.com" {
+			t.Errorf("expected X-Forwarded-User=ws-user@example.com, got %q", forwardedUser)
+		}
+	})
+
+	t.Run("plain_http_does_not_bypass", func(t *testing.T) {
+		// Sanity: requests without Upgrade headers must NOT hit the WS
+		// bypass branch (otherwise the new code path could short-circuit
+		// normal authentication).
+		oidc := newOidc(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			t.Fatal("backend must not be called for unauthenticated plain HTTP")
+		}))
+		req := httptest.NewRequest("GET", "/ws", nil)
+		req.Header.Set("Connection", "keep-alive")
+		rw := httptest.NewRecorder()
+		oidc.ServeHTTP(rw, req)
+		if rw.Code == http.StatusOK {
+			t.Errorf("expected redirect or 401 for plain HTTP without auth, got 200")
+		}
+	})
 }
 
 // TestServeHTTP_InitializationTimeout tests initialization timeout handling
diff --git a/middleware.go b/middleware.go
index 7ee012d..fa636f8 100644
--- a/middleware.go
+++ b/middleware.go
@@ -14,21 +14,40 @@ import (
 )
 
 // bypassReason describes why a request is being forwarded without OIDC auth.
-// It is only used for logging and to decide whether extra SSE-specific work
+// It is only used for logging and to decide whether extra side-effects
 // (propagating the user header from an existing session) should run.
 const (
-	bypassReasonExcluded = "excluded-url"
-	bypassReasonSSE      = "sse"
+	bypassReasonExcluded  = "excluded-url"
+	bypassReasonSSE       = "sse"
+	bypassReasonWebSocket = "websocket"
 )
 
+// isWebSocketUpgrade reports whether req is a WebSocket upgrade handshake
+// (RFC 6455). The middleware can only see the handshake; once Traefik
+// completes the upgrade it forwards frames directly, so we never re-process
+// per-frame traffic. We bypass auth on the handshake the same way we do for
+// SSE, because browser WebSocket clients cannot follow an OIDC redirect.
+func isWebSocketUpgrade(req *http.Request) bool {
+	if !strings.EqualFold(req.Header.Get("Upgrade"), "websocket") {
+		return false
+	}
+	for _, token := range strings.Split(req.Header.Get("Connection"), ",") {
+		if strings.EqualFold(strings.TrimSpace(token), "upgrade") {
+			return true
+		}
+	}
+	return false
+}
+
 // shouldBypassAuth decides whether a request must skip OIDC authentication
 // entirely. It returns (true, reason) when either the request path matches a
-// configured excluded URL or the Accept header asks for a text/event-stream
-// response (SSE). The reason lets ServeHTTP apply any side-effects that are
-// unique to the bypass kind (e.g. propagating user headers for SSE).
+// configured excluded URL, the Accept header asks for a text/event-stream
+// response (SSE), or the request is a WebSocket upgrade handshake. The
+// reason lets ServeHTTP apply any side-effects that are unique to the bypass
+// kind (e.g. propagating user headers).
 //
-// This must be called BEFORE waiting on t.initComplete so excluded and SSE
-// traffic is never blocked by a slow/broken provider.
+// This must be called BEFORE waiting on t.initComplete so excluded, SSE and
+// WebSocket traffic is never blocked by a slow/broken provider.
 func (t *TraefikOidc) shouldBypassAuth(req *http.Request) (bool, string) {
 	if t.determineExcludedURL(req.URL.Path) {
 		return true, bypassReasonExcluded
@@ -36,38 +55,55 @@ func (t *TraefikOidc) shouldBypassAuth(req *http.Request) (bool, string) {
 	if strings.Contains(req.Header.Get("Accept"), "text/event-stream") {
 		return true, bypassReasonSSE
 	}
+	if isWebSocketUpgrade(req) {
+		return true, bypassReasonWebSocket
+	}
 	return false, ""
 }
 
-// applySSEUserHeaders attempts to copy the authenticated user's identity from
-// an existing session onto the outgoing SSE request so downstream services
-// can still see who the user is. Failures are logged (not silenced) because
-// they indicate either a corrupt cookie or a misconfigured session manager
-// and are useful for debugging, but they never block the bypass itself.
-func (t *TraefikOidc) applySSEUserHeaders(req *http.Request) {
+// applyBypassUserHeaders enforces authentication on SSE / WebSocket bypass
+// requests and, on success, copies the authenticated user's identity onto
+// the outgoing request so downstream services can see who the user is.
+//
+// Returns true when the request carries a valid authenticated session and
+// the bypass should proceed. Returns false when no usable session is
+// present; callers must then reject the request (typically with 401) to
+// prevent unauthenticated traffic from reaching the backend just by setting
+// `Accept: text/event-stream` or sending a WebSocket upgrade.
+//
+// The check is cookie-only: the session cookie is sealed by our encryption
+// key, so the authenticated flag cannot be forged. We do NOT run full token
+// signature verification here so that SSE/WS keeps working when the OIDC
+// provider is briefly unavailable for JWK fetches.
+func (t *TraefikOidc) applyBypassUserHeaders(req *http.Request, reason string) bool {
 	if t.sessionManager == nil {
-		return
+		return false
 	}
 
 	session, err := t.sessionManager.GetSession(req)
 	if err != nil {
-		// Intentionally not fatal: SSE requests bypass auth, we just lose the
-		// forwarded-user header for this request.
-		t.logger.Debugf("SSE bypass: unable to load session for user header propagation: %v", err)
-		return
+		t.logger.Debugf("%s bypass: unable to load session: %v", reason, err)
+		return false
 	}
 	defer session.returnToPoolSafely()
 
+	if !session.GetAuthenticated() {
+		t.logger.Debugf("%s bypass: rejecting request without authenticated session", reason)
+		return false
+	}
+
 	email := session.GetEmail()
 	if email == "" {
-		return
+		t.logger.Debugf("%s bypass: rejecting request, session has no user identifier", reason)
+		return false
 	}
 
 	req.Header.Set("X-Forwarded-User", email)
 	if !t.minimalHeaders {
 		req.Header.Set("X-Auth-Request-User", email)
 	}
-	t.logger.Debugf("SSE bypass: forwarded user %s from session", email)
+	t.logger.Debugf("%s bypass: forwarded user %s from session", reason, email)
+	return true
 }
 
 // ServeHTTP implements the main middleware logic for processing HTTP requests.
@@ -124,16 +160,32 @@ func (t *TraefikOidc) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		t.firstRequestMutex.Unlock()
 	}
 
-	// Evaluate auth-bypass once, before waiting for initialization. Excluded URLs
-	// and SSE requests must not block on provider init. For SSE we additionally
-	// attempt to forward the user identity from an existing session (best
-	// effort) so downstream handlers still see X-Forwarded-User.
+	// Evaluate auth-bypass once, before waiting for initialization. Excluded
+	// URLs, SSE and WebSocket upgrade requests must not block on provider
+	// init. For SSE/WebSocket we ALSO require an authenticated session
+	// (cookie-only check, no JWK fetch) and otherwise return 401 — clients
+	// of in-flight streams can't follow an OIDC redirect, so forwarding
+	// unauthenticated traffic would silently expose the backend.
 	if bypass, reason := t.shouldBypassAuth(req); bypass {
 		t.logger.Debugf("Bypassing OIDC for %s (%s)", req.URL.Path, reason)
-		if reason == bypassReasonSSE {
-			t.applySSEUserHeaders(req)
+		switch reason {
+		case bypassReasonExcluded:
+			// Operator-declared excluded URLs forward unconditionally.
+			t.next.ServeHTTP(rw, req)
+		case bypassReasonSSE, bypassReasonWebSocket:
+			// Skip the OIDC redirect dance (clients can't follow it
+			// mid-stream) but still require an authenticated session.
+			// Otherwise an unauthenticated client could hit the backend
+			// just by setting Accept: text/event-stream or sending a
+			// WebSocket upgrade.
+			if !t.applyBypassUserHeaders(req, reason) {
+				t.sendErrorResponse(rw, req, "Authentication required", http.StatusUnauthorized)
+				return
+			}
+			t.next.ServeHTTP(rw, req)
+		default:
+			t.next.ServeHTTP(rw, req)
 		}
-		t.next.ServeHTTP(rw, req)
 		return
 	}
 
@@ -386,31 +438,52 @@ func (t *TraefikOidc) processAuthorizedRequest(rw http.ResponseWriter, req *http
 		}
 	}
 
-	tokenForClaims := session.GetIDToken()
-	if tokenForClaims == "" {
-		tokenForClaims = session.GetAccessToken()
-		if tokenForClaims == "" && len(t.allowedRolesAndGroups) > 0 {
-			t.logger.Error("No token available but roles/groups checks are required")
-			// Reset redirect count to prevent loops when token is missing
+	// Resolve ID-token claims at most once per request. SessionData caches
+	// the parsed claims keyed on the raw ID token, so concurrent dashboard
+	// panel requests on the same session don't repeatedly base64-decode and
+	// JSON-unmarshal the same JWT (a real cost under the yaegi interpreter
+	// that hosts Traefik plugins). idClaims is reused below by the
+	// header-templates branch.
+	idToken := session.GetIDToken()
+	var (
+		idClaims    map[string]interface{}
+		idClaimsErr error
+	)
+	if idToken != "" {
+		idClaims, idClaimsErr = session.GetIDTokenClaims(t.extractClaimsFunc)
+	}
+
+	// Choose which claims drive groups/roles extraction. Prefer the ID
+	// token (cached) and fall back to the access token if there is no ID
+	// token in the session — matching the prior behavior for opaque
+	// ID-token providers.
+	var (
+		groupClaims    map[string]interface{}
+		groupClaimsErr error
+	)
+	if idToken != "" {
+		groupClaims, groupClaimsErr = idClaims, idClaimsErr
+	} else if accessToken := session.GetAccessToken(); accessToken != "" {
+		groupClaims, groupClaimsErr = t.extractClaimsFunc(accessToken)
+	} else if len(t.allowedRolesAndGroups) > 0 {
+		t.logger.Error("No token available but roles/groups checks are required")
+		session.ResetRedirectCount()
+		t.defaultInitiateAuthentication(rw, req, session, redirectURL)
+		return
+	}
+
+	var groups, roles []string
+
+	if groupClaimsErr == nil && groupClaims != nil {
+		var err error
+		groups, roles, err = t.extractGroupsAndRolesFromClaims(groupClaims)
+		if err != nil && len(t.allowedRolesAndGroups) > 0 {
+			t.logger.Errorf("Failed to extract groups and roles: %v", err)
 			session.ResetRedirectCount()
 			t.defaultInitiateAuthentication(rw, req, session, redirectURL)
 			return
 		}
-	}
-
-	// Initialize empty slices
-	var groups, roles []string
-
-	if tokenForClaims != "" {
-		var err error
-		groups, roles, err = t.extractGroupsAndRoles(tokenForClaims)
-		if err != nil && len(t.allowedRolesAndGroups) > 0 {
-			t.logger.Errorf("Failed to extract groups and roles: %v", err)
-			// Reset redirect count to prevent loops when claim extraction fails
-			session.ResetRedirectCount()
-			t.defaultInitiateAuthentication(rw, req, session, redirectURL)
-			return
-		} else if err == nil {
+		if err == nil {
 			if len(groups) > 0 {
 				req.Header.Set("X-User-Groups", strings.Join(groups, ","))
 			}
@@ -442,41 +515,40 @@ func (t *TraefikOidc) processAuthorizedRequest(rw http.ResponseWriter, req *http
 	if !t.minimalHeaders {
 		req.Header.Set("X-Auth-Request-Redirect", req.URL.RequestURI())
 		req.Header.Set("X-Auth-Request-User", email)
-		if idToken := session.GetIDToken(); idToken != "" {
+		if idToken != "" {
 			req.Header.Set("X-Auth-Request-Token", idToken)
 		}
 	}
 
 	if len(t.headerTemplates) > 0 {
-		// Reuse claims parsed earlier in this request if the ID token has not
-		// changed. Saves an unnecessary JWT parse on every authenticated
-		// request that uses headerTemplates.
-		claims, err := session.GetIDTokenClaims(t.extractClaimsFunc)
-		if err != nil {
-			t.logger.Errorf("Failed to extract claims from ID Token for template headers: %v", err)
+		if idClaimsErr != nil {
+			t.logger.Errorf("Failed to extract claims from ID Token for template headers: %v", idClaimsErr)
 		} else {
+			// idClaims may be nil when no ID token is present; templates
+			// referencing .Claims.* will simply produce empty values, which
+			// matches the prior behavior.
 			templateData := map[string]interface{}{
 				"AccessToken":  session.GetAccessToken(),
-				"IDToken":      session.GetIDToken(),
+				"IDToken":      idToken,
 				"RefreshToken": session.GetRefreshToken(),
-				"Claims":       claims,
+				"Claims":       idClaims,
 			}
 
 			for headerName, tmpl := range t.headerTemplates {
 				var buf bytes.Buffer
-
 				if err := tmpl.Execute(&buf, templateData); err != nil {
 					t.logger.Errorf("Failed to execute template for header %s: %v", headerName, err)
 					continue
 				}
 				headerValue := buf.String()
-
 				req.Header.Set(headerName, headerValue)
-
 				t.logger.Debugf("Set templated header %s = %s", headerName, headerValue)
 			}
-			session.MarkDirty()
-			t.logger.Debugf("Session marked dirty after templated header processing.")
+			// NOTE: templates only mutate request headers (not session state),
+			// so we deliberately do NOT MarkDirty / Save here. Previously every
+			// authenticated request with header templates re-encrypted and
+			// rewrote all session cookies, which was a measurable CPU and
+			// Set-Cookie tax on dashboards that poll many panels per second.
 		}
 	}
 
diff --git a/token_manager.go b/token_manager.go
index f0e5e9f..a20fcaf 100644
--- a/token_manager.go
+++ b/token_manager.go
@@ -11,6 +11,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"runtime"
 	"strings"
 	"time"
 )
@@ -1193,9 +1194,14 @@ func (t *TraefikOidc) startTokenCleanup() {
 	sessionManager := t.sessionManager
 	logger := t.logger
 
+	// Only use the fast cleanup interval when actually running under `go test`.
+	// runtime.Compiler == "yaegi" makes isTestMode() return true in production
+	// (Traefik interprets the plugin via yaegi), which would otherwise pin this
+	// ticker to 20 Hz on a real cluster despite tokenCache.Cleanup and
+	// jwkCache.Cleanup both being no-ops there.
 	cleanupInterval := 1 * time.Minute
-	if isTestMode() {
-		cleanupInterval = 50 * time.Millisecond // Fast interval for tests
+	if isTestMode() && runtime.Compiler != "yaegi" {
+		cleanupInterval = 50 * time.Millisecond
 	}
 
 	// Create cleanup function
@@ -1237,25 +1243,27 @@ func (t *TraefikOidc) startTokenCleanup() {
 }
 
 // extractGroupsAndRoles extracts group and role information from token claims.
-// It parses the 'groups' and 'roles' claims from the ID token and validates their format.
-// Parameters:
-//   - idToken: The ID token containing claims to extract.
+// It parses the configured group/role claims from the supplied ID token.
 //
-// Returns:
-//   - groups: Array of group names from the 'groups' claim.
-//   - roles: Array of role names from the 'roles' claim.
-//   - An error if claim extraction fails or if the 'groups' or 'roles' claims are present
-//     but not arrays of strings.
+// Most callers should prefer extractGroupsAndRolesFromClaims when claims have
+// already been parsed for the request (e.g. via SessionData.GetIDTokenClaims),
+// to avoid re-parsing the JWT.
 func (t *TraefikOidc) extractGroupsAndRoles(idToken string) ([]string, []string, error) {
 	claims, err := t.extractClaimsFunc(idToken)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to extract claims: %w", err)
 	}
+	return t.extractGroupsAndRolesFromClaims(claims)
+}
 
+// extractGroupsAndRolesFromClaims extracts group and role information from
+// already-parsed claims. Hot path: callers that have a cached claims map (such
+// as SessionData.GetIDTokenClaims) should use this to skip a redundant
+// base64+JSON decode of the JWT on every authenticated request.
+func (t *TraefikOidc) extractGroupsAndRolesFromClaims(claims map[string]interface{}) ([]string, []string, error) {
 	var groups []string
 	var roles []string
 
-	// Extract groups using configurable claim name (defaults to "groups")
 	if groupsClaim, exists := claims[t.groupClaimName]; exists {
 		groupsSlice, ok := groupsClaim.([]interface{})
 		if !ok {
@@ -1271,7 +1279,6 @@ func (t *TraefikOidc) extractGroupsAndRoles(idToken string) ([]string, []string,
 		}
 	}
 
-	// Extract roles using configurable claim name (defaults to "roles")
 	if rolesClaim, exists := claims[t.roleClaimName]; exists {
 		rolesSlice, ok := rolesClaim.([]interface{})
 		if !ok {