Bugfix: Refresh token not obtained when access token is expired.

* Improve refresh token handling in the background.

Resolves issue when user opens the website, allows the access token to expire, but continues browsing.
The background requests are failing with CORS errors to OIDC provider.

* fixup! Improve refresh token handling in the background.

* Abstract the token blacklisting.

.traefik.yml

@@ -62,6 +62,7 @@ testData:
   # Advanced parameters (usually discovered automatically from provider metadata)
   revocationURL: https://accounts.google.com/revoke # Endpoint for revoking tokens
   oidcEndSessionURL: https://accounts.google.com/logout # Provider's end session endpoint
+  enablePKCE: false # Enables PKCE (Proof Key for Code Exchange) for additional security
 
 # Configuration documentation
 configuration:
@@ -230,3 +231,15 @@ configuration:
 
       Example: https://accounts.google.com/logout
     required: false
+
+  enablePKCE:
+    type: boolean
+    description: |
+      Enables PKCE (Proof Key for Code Exchange) for the OAuth 2.0 authorization code flow.
+      PKCE adds an extra layer of security to protect against authorization code interception attacks.
+
+      Not all OIDC providers support PKCE, so this should only be enabled if your provider supports it.
+      If enabled, the middleware will generate and use a code verifier/challenge pair during authentication.
+
+      Default: false
+    required: false

README.md

@@ -71,11 +71,13 @@ The middleware supports the following configuration options:
 | `logLevel` | Sets the logging verbosity | `info` | `debug`, `info`, `error` |
 | `forceHTTPS` | Forces the use of HTTPS for all URLs | `true` | `true`, `false` |
 | `rateLimit` | Sets the maximum number of requests per second | `100` | `500` |
-| `excludedURLs` | Lists paths that bypass authentication | `["/favicon"]` | `["/health", "/metrics", "/public"]` |
+| `excludedURLs` | Lists paths that bypass authentication | none | `["/health", "/metrics", "/public"]` |
 | `allowedUserDomains` | Restricts access to specific email domains | none | `["company.com", "subsidiary.com"]` |
 | `allowedRolesAndGroups` | Restricts access to users with specific roles or groups | none | `["admin", "developer"]` |
 | `revocationURL` | The endpoint for revoking tokens | auto-discovered | `https://accounts.google.com/revoke` |
 | `oidcEndSessionURL` | The provider's end session endpoint | auto-discovered | `https://accounts.google.com/logout` |
+| `enablePKCE` | Enables PKCE (Proof Key for Code Exchange) for authorization code flow | `false` | `true`, `false` |
+| `refreshGracePeriodSeconds` | Seconds before token expiry to attempt proactive refresh | `60` | `120` |
 
 ## Usage Examples
 
@@ -233,6 +235,30 @@ spec:
         - profile
 ```
 
+### With PKCE Enabled
+
+```yaml
+apiVersion: traefik.io/v1alpha1
+kind: Middleware
+metadata:
+  name: oidc-with-pkce
+  namespace: traefik
+spec:
+  plugin:
+    traefikoidc:
+      providerURL: https://accounts.google.com
+      clientID: 1234567890.apps.googleusercontent.com
+      clientSecret: your-client-secret
+      sessionEncryptionKey: potato-secret-is-at-least-32-bytes-long
+      callbackURL: /oauth2/callback
+      logoutURL: /oauth2/logout
+      enablePKCE: true  # Enables PKCE for added security
+      scopes:
+        - openid
+        - email
+        - profile
+```
+
 ### Keeping Secrets Secret in Kubernetes
 
 For Kubernetes environments, you can reference secrets instead of hardcoding sensitive values:
@@ -378,6 +404,17 @@ http:
 
 The middleware uses encrypted cookies to manage user sessions. The `sessionEncryptionKey` must be at least 32 bytes long and should be kept secret.
 
+### PKCE Support
+
+The middleware supports PKCE (Proof Key for Code Exchange), which is an extension to the authorization code flow to prevent authorization code interception attacks. When enabled via the `enablePKCE` option, the middleware will generate a code verifier for each authentication request and derive a code challenge from it. The code verifier is stored in the user's session and sent during the token exchange process.
+
+PKCE is recommended when:
+- Your OIDC provider supports it (most modern providers do)
+- You need an additional layer of security for the authorization code flow
+- You're concerned about potential authorization code interception attacks
+
+Note that not all OIDC providers support PKCE, so check your provider's documentation before enabling this feature.
+
 ### Token Caching and Blacklisting
 
 The middleware automatically caches validated tokens to improve performance and maintains a blacklist of revoked tokens.

autocleanup.go

@@ -2,8 +2,16 @@ package traefikoidc
 
 import "time"
 
-// autoCleanupRoutine runs a ticker that calls the provided cleanup function at the specified interval.
-// It stops when a value is received on the stop channel.
+// autoCleanupRoutine periodically calls the provided cleanup function.
+// It starts a ticker with the given interval and executes the cleanup function
+// on each tick. The routine stops gracefully when a signal is received on the
+// stop channel. This is typically used for background cleanup tasks like
+// expiring cache entries.
+//
+// Parameters:
+//   - interval: The time duration between cleanup calls.
+//   - stop: A channel used to signal the routine to stop. Receiving any value will terminate the loop.
+//   - cleanup: The function to call periodically for cleanup tasks.
 func autoCleanupRoutine(interval time.Duration, stop <-chan struct{}, cleanup func()) {
 	ticker := time.NewTicker(interval)
 	defer ticker.Stop()

blacklist.go

@@ -1,110 +0,0 @@
-package traefikoidc
-
-import (
-	"sync"
-	"time"
-)
-
-// TokenBlacklist manages a thread-safe list of revoked tokens with expiration.
-type TokenBlacklist struct {
-	tokens map[string]time.Time
-	mutex  sync.RWMutex
-}
-
-// NewTokenBlacklist creates a new token blacklist instance.
-func NewTokenBlacklist() *TokenBlacklist {
-	return &TokenBlacklist{
-		tokens: make(map[string]time.Time),
-	}
-}
-
-// Add adds a token to the blacklist with an expiration time.
-func (b *TokenBlacklist) Add(token string, expiry time.Time) {
-	b.mutex.Lock()
-	defer b.mutex.Unlock()
-
-	// Clean up expired tokens if we're at capacity
-	if len(b.tokens) >= 1000 {
-		now := time.Now()
-		futureThreshold := now.Add(time.Minute)
-		for t, exp := range b.tokens {
-			if now.After(exp) || futureThreshold.After(exp) {
-				delete(b.tokens, t)
-			}
-		}
-
-		// If still at capacity, remove oldest token
-		if len(b.tokens) >= 1000 {
-			var oldestToken string
-			var oldestTime time.Time
-			first := true
-			for t, exp := range b.tokens {
-				if first || exp.Before(oldestTime) {
-					oldestToken = t
-					oldestTime = exp
-					first = false
-				}
-			}
-			if oldestToken != "" {
-				delete(b.tokens, oldestToken)
-			}
-		}
-	}
-
-	b.tokens[token] = expiry
-}
-
-// IsBlacklisted checks if a token is in the blacklist and not expired.
-func (b *TokenBlacklist) IsBlacklisted(token string) bool {
-	b.mutex.RLock()
-	defer b.mutex.RUnlock()
-
-	expiry, exists := b.tokens[token]
-	if !exists {
-		return false
-	}
-
-	// If token is expired, remove it and return false
-	if time.Now().After(expiry) {
-		// Switch to write lock to remove expired token
-		b.mutex.RUnlock()
-		b.mutex.Lock()
-		delete(b.tokens, token)
-		b.mutex.Unlock()
-		b.mutex.RLock()
-		return false
-	}
-
-	return true
-}
-
-// Cleanup removes expired tokens from the blacklist.
-// Also removes tokens that will expire within the next minute to prevent edge cases.
-func (b *TokenBlacklist) Cleanup() {
-	b.mutex.Lock()
-	defer b.mutex.Unlock()
-
-	now := time.Now()
-	futureThreshold := now.Add(time.Minute)
-
-	for token, expiry := range b.tokens {
-		// Remove tokens that are expired or will expire soon
-		if now.After(expiry) || futureThreshold.After(expiry) {
-			delete(b.tokens, token)
-		}
-	}
-}
-
-// Remove removes a token from the blacklist regardless of its expiration.
-func (b *TokenBlacklist) Remove(token string) {
-	b.mutex.Lock()
-	defer b.mutex.Unlock()
-	delete(b.tokens, token)
-}
-
-// Count returns the current number of tokens in the blacklist.
-func (b *TokenBlacklist) Count() int {
-	b.mutex.RLock()
-	defer b.mutex.RUnlock()
-	return len(b.tokens)
-}

blacklist_test.go

@@ -1,74 +0,0 @@
-package traefikoidc
-
-import (
-	"testing"
-	"time"
-)
-
-func TestTokenBlacklist_Add(t *testing.T) {
-	blacklist := NewTokenBlacklist()
-	token := "testToken"
-	expiry := time.Now().Add(time.Hour)
-
-	blacklist.Add(token, expiry)
-
-	if !blacklist.IsBlacklisted(token) {
-		t.Errorf("Expected token to be blacklisted, but it was not")
-	}
-}
-
-func TestTokenBlacklist_IsBlacklisted(t *testing.T) {
-	blacklist := NewTokenBlacklist()
-	token := "testToken"
-	expiry := time.Now().Add(time.Hour)
-
-	blacklist.Add(token, expiry)
-
-	if !blacklist.IsBlacklisted(token) {
-		t.Errorf("Expected token to be blacklisted, but it was not")
-	}
-
-	if blacklist.IsBlacklisted("nonExistentToken") {
-		t.Errorf("Expected non-existent token to not be blacklisted, but it was")
-	}
-}
-
-func TestTokenBlacklist_Cleanup(t *testing.T) {
-	blacklist := NewTokenBlacklist()
-	token := "testToken"
-	expiry := time.Now().Add(-time.Hour) // Expired token
-
-	blacklist.Add(token, expiry)
-	blacklist.Cleanup()
-
-	if blacklist.IsBlacklisted(token) {
-		t.Errorf("Expected expired token to be removed after cleanup, but it was not")
-	}
-}
-
-func TestTokenBlacklist_Remove(t *testing.T) {
-	blacklist := NewTokenBlacklist()
-	token := "testToken"
-	expiry := time.Now().Add(time.Hour)
-
-	blacklist.Add(token, expiry)
-	blacklist.Remove(token)
-
-	if blacklist.IsBlacklisted(token) {
-		t.Errorf("Expected token to be removed, but it was not")
-	}
-}
-
-func TestTokenBlacklist_Count(t *testing.T) {
-	blacklist := NewTokenBlacklist()
-	token1 := "token1"
-	token2 := "token2"
-	expiry := time.Now().Add(time.Hour)
-
-	blacklist.Add(token1, expiry)
-	blacklist.Add(token2, expiry)
-
-	if blacklist.Count() != 2 {
-		t.Errorf("Expected blacklist count to be 2, but got %d", blacklist.Count())
-	}
-}

cache.go

@@ -46,7 +46,9 @@ type Cache struct {
 // DefaultMaxSize is the default maximum number of items in the cache.
 const DefaultMaxSize = 500
 
-// NewCache creates a new empty cache instance that is ready for use.
+// NewCache creates a new empty cache instance with default settings.
+// It initializes the internal maps and list, sets the default maximum size,
+// and starts the automatic cleanup goroutine.
 func NewCache() *Cache {
 	c := &Cache{
 		items:               make(map[string]CacheItem, DefaultMaxSize),
@@ -60,8 +62,12 @@ func NewCache() *Cache {
 	return c
 }
 
-// Set adds or updates an item in the cache with the specified expiration duration.
-// It moves the item to the most recently used position.
+// Set adds or updates an item in the cache with the specified key, value, and expiration duration.
+// If the key already exists, its value and expiration time are updated, and it's moved
+// to the most recently used position in the LRU list.
+// If the key does not exist and the cache is full, the least recently used item is evicted
+// before adding the new item.
+// The expiration duration is relative to the time Set is called.
 func (c *Cache) Set(key string, value interface{}, expiration time.Duration) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
@@ -95,8 +101,11 @@ func (c *Cache) Set(key string, value interface{}, expiration time.Duration) {
 	c.elems[key] = elem
 }
 
-// Get retrieves an item from the cache if it exists and hasn't expired.
-// Moving the accessed item to the most recently used position.
+// Get retrieves an item from the cache by its key.
+// If the item exists and has not expired, its value and true are returned.
+// Accessing an item moves it to the most recently used position in the LRU list.
+// If the item does not exist or has expired, nil and false are returned, and the
+// expired item is removed from the cache.
 func (c *Cache) Get(key string) (interface{}, bool) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
@@ -120,7 +129,9 @@ func (c *Cache) Get(key string) (interface{}, bool) {
 	return item.Value, true
 }
 
-// Delete removes an item from the cache.
+// Delete removes an item from the cache by its key.
+// If the key exists, the corresponding item is removed from the cache storage
+// and the LRU list.
 func (c *Cache) Delete(key string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
@@ -128,8 +139,10 @@ func (c *Cache) Delete(key string) {
 	c.removeItem(key)
 }
 
-// Cleanup removes all expired items from the cache. This should be called periodically
-// to prevent memory bloat from expired entries.
+// Cleanup iterates through the cache and removes all items that have expired.
+// An item is considered expired if the current time is after its ExpiresAt timestamp.
+// This method is called automatically by the auto-cleanup goroutine, but can also
+// be called manually.
 func (c *Cache) Cleanup() {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
@@ -143,7 +156,11 @@ func (c *Cache) Cleanup() {
 	}
 }
 
-// evictOldest removes the least recently used item from the cache.
+// evictOldest removes the least recently used (oldest) item from the cache.
+// It first attempts to find and remove an expired item from the front of the LRU list.
+// If no expired items are found at the front, it removes the absolute oldest item (front of the list).
+// This method is called internally by Set when the cache reaches its maximum size.
+// Note: This function assumes the write lock is already held.
 func (c *Cache) evictOldest() {
 	now := time.Now()
 	elem := c.order.Front()
@@ -167,7 +184,9 @@ func (c *Cache) evictOldest() {
 	}
 }
 
-// removeItem removes an item from both the cache and the LRU tracking structures.
+// removeItem removes an item specified by the key from the cache's internal storage (items map)
+// and its corresponding entry from the LRU list (order list and elems map).
+// Note: This function assumes the write lock is already held.
 func (c *Cache) removeItem(key string) {
 	delete(c.items, key)
 	if elem, ok := c.elems[key]; ok {
@@ -176,12 +195,15 @@ func (c *Cache) removeItem(key string) {
 	}
 }
 
-// startAutoCleanup initiates a goroutine that periodically cleans up expired cache items.
+// startAutoCleanup starts the background goroutine that automatically calls the Cleanup method
+// at the interval specified by c.autoCleanupInterval.
+// It uses the autoCleanupRoutine helper function.
 func (c *Cache) startAutoCleanup() {
 	autoCleanupRoutine(c.autoCleanupInterval, c.stopCleanup, c.Cleanup)
 }
 
-// Close terminates the auto cleanup goroutine.
+// Close stops the automatic cleanup goroutine associated with this cache instance.
+// It should be called when the cache is no longer needed to prevent resource leaks.
 func (c *Cache) Close() {
 	close(c.stopCleanup)
 }

helpers.go

@@ -3,6 +3,7 @@ package traefikoidc
 import (
 	"context"
 	"crypto/rand"
+	"crypto/sha256"
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
@@ -14,10 +15,14 @@ import (
 	"time"
 )
 
-// generateNonce creates a cryptographically secure random nonce
-// for use in the OIDC authentication flow. The nonce is used to
-// prevent replay attacks by ensuring the token received matches
-// the authentication request.
+// generateNonce creates a cryptographically secure random string suitable for use as an OIDC nonce.
+// The nonce is used during the authentication flow to mitigate replay attacks by associating
+// the ID token with the specific authentication request.
+// It generates 32 random bytes and encodes them using base64 URL encoding.
+//
+// Returns:
+//   - A base64 URL encoded random string (nonce).
+//   - An error if the random byte generation fails.
 func generateNonce() (string, error) {
 	nonceBytes := make([]byte, 32)
 	_, err := rand.Read(nonceBytes)
@@ -27,6 +32,42 @@ func generateNonce() (string, error) {
 	return base64.URLEncoding.EncodeToString(nonceBytes), nil
 }
 
+// generateCodeVerifier creates a cryptographically secure random string suitable for use as a PKCE code verifier.
+// According to RFC 7636, the verifier should be a high-entropy string between 43 and 128 characters long.
+// This function generates 32 random bytes, resulting in a 43-character base64 URL encoded string.
+//
+// Returns:
+//   - A base64 URL encoded random string (code verifier).
+//   - An error if the random byte generation fails.
+func generateCodeVerifier() (string, error) {
+	// Using 32 bytes (256 bits) will produce a 43 character base64url string
+	verifierBytes := make([]byte, 32)
+	_, err := rand.Read(verifierBytes)
+	if err != nil {
+		return "", fmt.Errorf("could not generate code verifier: %w", err)
+	}
+	return base64.RawURLEncoding.EncodeToString(verifierBytes), nil
+}
+
+// deriveCodeChallenge computes the PKCE code challenge from a given code verifier.
+// It uses the S256 challenge method (SHA-256 hash followed by base64 URL encoding)
+// as defined in RFC 7636.
+//
+// Parameters:
+//   - codeVerifier: The high-entropy string generated by generateCodeVerifier.
+//
+// Returns:
+//   - The base64 URL encoded SHA-256 hash of the code verifier (code challenge).
+func deriveCodeChallenge(codeVerifier string) string {
+	// Calculate SHA-256 hash of the code verifier
+	hasher := sha256.New()
+	hasher.Write([]byte(codeVerifier))
+	hash := hasher.Sum(nil)
+
+	// Base64url encode the hash to get the code challenge
+	return base64.RawURLEncoding.EncodeToString(hash)
+}
+
 // TokenResponse represents the response from the OIDC token endpoint.
 // It contains the various tokens and metadata returned after successful
 // code exchange or token refresh operations.
@@ -47,14 +88,23 @@ type TokenResponse struct {
 	TokenType string `json:"token_type"`
 }
 
-// exchangeTokens performs the OAuth 2.0 token exchange with the OIDC provider.
-// It supports both authorization code and refresh token grant types.
+// exchangeTokens performs the OAuth 2.0 token exchange with the OIDC provider's token endpoint.
+// It handles both the "authorization_code" grant type (exchanging an authorization code for tokens)
+// and the "refresh_token" grant type (using a refresh token to obtain new tokens).
+// It includes necessary parameters like client credentials and handles PKCE verification if applicable.
+// The function follows redirects and handles potential errors during the exchange.
+//
 // Parameters:
-//   - ctx: Context for the HTTP request
-//   - grantType: The OAuth 2.0 grant type ("authorization_code" or "refresh_token")
-//   - codeOrToken: Either the authorization code or refresh token
-//   - redirectURL: The callback URL for authorization code grant
-func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType, codeOrToken, redirectURL string) (*TokenResponse, error) {
+//   - ctx: The context for the outgoing HTTP request.
+//   - grantType: The OAuth 2.0 grant type ("authorization_code" or "refresh_token").
+//   - codeOrToken: The authorization code (for "authorization_code" grant) or the refresh token (for "refresh_token" grant).
+//   - redirectURL: The redirect URI that was used in the initial authorization request (required for "authorization_code" grant).
+//   - codeVerifier: The PKCE code verifier (required for "authorization_code" grant if PKCE was used).
+//
+// Returns:
+//   - A TokenResponse containing the obtained tokens (ID, access, refresh).
+//   - An error if the token exchange fails (e.g., network error, provider error, invalid grant).
+func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, codeOrToken string, redirectURL string, codeVerifier string) (*TokenResponse, error) {
 	data := url.Values{
 		"grant_type":    {grantType},
 		"client_id":     {t.clientID},
@@ -64,6 +114,11 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType, codeOrToken
 	if grantType == "authorization_code" {
 		data.Set("code", codeOrToken)
 		data.Set("redirect_uri", redirectURL)
+
+		// Add code_verifier if PKCE is being used
+		if codeVerifier != "" {
+			data.Set("code_verifier", codeVerifier)
+		}
 	} else if grantType == "refresh_token" {
 		data.Set("refresh_token", codeOrToken)
 	}
@@ -108,11 +163,19 @@ func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType, codeOrToken
 	return &tokenResponse, nil
 }
 
-// getNewTokenWithRefreshToken obtains new tokens using a refresh token.
-// This is used to refresh access tokens before they expire.
+// getNewTokenWithRefreshToken uses a refresh token to obtain a new set of tokens (ID, access, refresh)
+// from the OIDC provider's token endpoint. It wraps the exchangeTokens function with the
+// "refresh_token" grant type.
+//
+// Parameters:
+//   - refreshToken: The refresh token previously obtained during authentication or a prior refresh.
+//
+// Returns:
+//   - A TokenResponse containing the newly obtained tokens.
+//   - An error if the refresh operation fails.
 func (t *TraefikOidc) getNewTokenWithRefreshToken(refreshToken string) (*TokenResponse, error) {
 	ctx := context.Background()
-	tokenResponse, err := t.exchangeTokens(ctx, "refresh_token", refreshToken, "")
+	tokenResponse, err := t.exchangeTokens(ctx, "refresh_token", refreshToken, "", "")
 	if err != nil {
 		return nil, fmt.Errorf("failed to refresh token: %w", err)
 	}
@@ -121,148 +184,17 @@ func (t *TraefikOidc) getNewTokenWithRefreshToken(refreshToken string) (*TokenRe
 	return tokenResponse, nil
 }
 
-// handleExpiredToken manages token expiration by clearing the session
-// and initiating a new authentication flow.
-func (t *TraefikOidc) handleExpiredToken(rw http.ResponseWriter, req *http.Request, session *SessionData, redirectURL string) {
-	// Clear authentication data but preserve CSRF state
-	session.SetAuthenticated(false)
-	session.SetAccessToken("")
-	session.SetRefreshToken("")
-	session.SetEmail("")
-
-	// Save the cleared session state
-	if err := session.Save(req, rw); err != nil {
-		t.logger.Errorf("Failed to save cleared session: %v", err)
-		http.Error(rw, "Internal Server Error", http.StatusInternalServerError)
-		return
-	}
-
-	t.defaultInitiateAuthentication(rw, req, session, redirectURL)
-}
-
-// handleCallback processes the authentication callback from the OIDC provider.
-// It validates the callback parameters, exchanges the authorization code for
-// tokens, verifies the tokens, and establishes the user's session.
-func (t *TraefikOidc) handleCallback(rw http.ResponseWriter, req *http.Request, redirectURL string) {
-	session, err := t.sessionManager.GetSession(req)
-	if err != nil {
-		t.logger.Errorf("Session error: %v", err)
-		http.Error(rw, "Session error", http.StatusInternalServerError)
-		return
-	}
-
-	t.logger.Debugf("Handling callback, URL: %s", req.URL.String())
-
-	// Check for errors in the callback
-	if req.URL.Query().Get("error") != "" {
-		errorDescription := req.URL.Query().Get("error_description")
-		t.logger.Errorf("Authentication error: %s - %s", req.URL.Query().Get("error"), errorDescription)
-		http.Error(rw, fmt.Sprintf("Authentication error: %s", errorDescription), http.StatusBadRequest)
-		return
-	}
-
-	// Validate CSRF state
-	state := req.URL.Query().Get("state")
-	if state == "" {
-		t.logger.Error("No state in callback")
-		http.Error(rw, "State parameter missing in callback", http.StatusBadRequest)
-		return
-	}
-
-	csrfToken := session.GetCSRF()
-	if csrfToken == "" {
-		t.logger.Error("CSRF token missing in session")
-		http.Error(rw, "CSRF token missing", http.StatusBadRequest)
-		return
-	}
-
-	if state != csrfToken {
-		t.logger.Error("State parameter does not match CSRF token in session")
-		http.Error(rw, "Invalid state parameter", http.StatusBadRequest)
-		return
-	}
-
-	// Exchange code for tokens
-	code := req.URL.Query().Get("code")
-	if code == "" {
-		t.logger.Error("No code in callback")
-		http.Error(rw, "No code in callback", http.StatusBadRequest)
-		return
-	}
-
-	tokenResponse, err := t.exchangeCodeForTokenFunc(code, redirectURL)
-	if err != nil {
-		t.logger.Errorf("Failed to exchange code for token: %v", err)
-		http.Error(rw, "Authentication failed", http.StatusInternalServerError)
-		return
-	}
-
-	// Verify tokens and claims
-	if err := t.verifyToken(tokenResponse.IDToken); err != nil {
-		t.logger.Errorf("Failed to verify id_token: %v", err)
-		http.Error(rw, "Authentication failed", http.StatusInternalServerError)
-		return
-	}
-
-	claims, err := t.extractClaimsFunc(tokenResponse.IDToken)
-	if err != nil {
-		t.logger.Errorf("Failed to extract claims: %v", err)
-		http.Error(rw, "Authentication failed", http.StatusInternalServerError)
-		return
-	}
-
-	// Verify nonce to prevent replay attacks
-	nonceClaim, ok := claims["nonce"].(string)
-	if !ok || nonceClaim == "" {
-		t.logger.Error("Nonce claim missing in id_token")
-		http.Error(rw, "Authentication failed", http.StatusInternalServerError)
-		return
-	}
-
-	sessionNonce := session.GetNonce()
-	if sessionNonce == "" {
-		t.logger.Error("Nonce not found in session")
-		http.Error(rw, "Authentication failed", http.StatusInternalServerError)
-		return
-	}
-
-	if nonceClaim != sessionNonce {
-		t.logger.Error("Nonce claim does not match session nonce")
-		http.Error(rw, "Authentication failed", http.StatusInternalServerError)
-		return
-	}
-
-	// Validate user's email domain
-	email, _ := claims["email"].(string)
-	if email == "" || !t.isAllowedDomain(email) {
-		t.logger.Errorf("Invalid or disallowed email: %s", email)
-		http.Error(rw, "Authentication failed: Invalid or disallowed email", http.StatusForbidden)
-		return
-	}
-
-	// Update session with authentication data
-	session.SetAuthenticated(true)
-	session.SetEmail(email)
-	session.SetAccessToken(tokenResponse.IDToken)
-	session.SetRefreshToken(tokenResponse.RefreshToken)
-
-	if err := session.Save(req, rw); err != nil {
-		t.logger.Errorf("Failed to save session: %v", err)
-		http.Error(rw, "Failed to save session", http.StatusInternalServerError)
-		return
-	}
-
-	// Redirect to original path or root
-	redirectPath := "/"
-	if incomingPath := session.GetIncomingPath(); incomingPath != "" && incomingPath != t.redirURLPath {
-		redirectPath = incomingPath
-	}
-
-	http.Redirect(rw, req, redirectPath, http.StatusFound)
-}
-
-// extractClaims parses a JWT token and extracts its claims.
-// It handles base64url decoding and JSON parsing of the token payload.
+// extractClaims decodes the payload (claims set) part of a JWT string.
+// It splits the JWT into its three parts, base64 URL decodes the second part (payload),
+// and unmarshals the resulting JSON into a map.
+// Note: This function does *not* validate the token's signature or claims.
+//
+// Parameters:
+//   - tokenString: The raw JWT string.
+//
+// Returns:
+//   - A map representing the JSON claims extracted from the token payload.
+//   - An error if the token format is invalid, decoding fails, or JSON unmarshaling fails.
 func extractClaims(tokenString string) (map[string]interface{}, error) {
 	parts := strings.Split(tokenString, ".")
 	if len(parts) != 3 {
@@ -290,21 +222,36 @@ type TokenCache struct {
 	cache *Cache
 }
 
-// NewTokenCache creates a new TokenCache instance.
+// NewTokenCache creates and initializes a new TokenCache.
+// It internally creates a new generic Cache instance for storage.
 func NewTokenCache() *TokenCache {
 	return &TokenCache{
 		cache: NewCache(),
 	}
 }
 
-// Set stores a token's claims in the cache with an expiration time.
+// Set stores the claims associated with a specific token string in the cache.
+// It prefixes the token string to avoid potential collisions with other cache types
+// and sets the provided expiration duration.
+//
+// Parameters:
+//   - token: The raw token string (used as the key).
+//   - claims: The map of claims associated with the token.
+//   - expiration: The duration for which the cache entry should be valid.
 func (tc *TokenCache) Set(token string, claims map[string]interface{}, expiration time.Duration) {
 	token = "t-" + token
 	tc.cache.Set(token, claims, expiration)
 }
 
-// Get retrieves a token's claims from the cache.
-// Returns the claims and a boolean indicating if the token was found.
+// Get retrieves the cached claims for a given token string.
+// It prefixes the token string before querying the underlying cache.
+//
+// Parameters:
+//   - token: The raw token string to look up.
+//
+// Returns:
+//   - The cached claims map if found and valid.
+//   - A boolean indicating whether the token was found in the cache (true if found, false otherwise).
 func (tc *TokenCache) Get(token string) (map[string]interface{}, bool) {
 	token = "t-" + token
 	value, found := tc.cache.Get(token)
@@ -315,29 +262,59 @@ func (tc *TokenCache) Get(token string) (map[string]interface{}, bool) {
 	return claims, ok
 }
 
-// Delete removes a token from the cache.
+// Delete removes the cached entry for a specific token string.
+// It prefixes the token string before calling the underlying cache's Delete method.
+//
+// Parameters:
+//   - token: The raw token string to remove from the cache.
 func (tc *TokenCache) Delete(token string) {
 	token = "t-" + token
 	tc.cache.Delete(token)
 }
 
-// Cleanup removes expired tokens from the cache.
+// Cleanup triggers the cleanup process for the underlying generic cache,
+// removing expired token entries.
 func (tc *TokenCache) Cleanup() {
 	tc.cache.Cleanup()
 }
 
-// exchangeCodeForToken exchanges an authorization code for tokens.
-func (t *TraefikOidc) exchangeCodeForToken(code string, redirectURL string) (*TokenResponse, error) {
+// exchangeCodeForToken is a convenience function that wraps exchangeTokens specifically
+// for the "authorization_code" grant type. It handles the conditional inclusion of the
+// PKCE code verifier based on the middleware's configuration (t.enablePKCE).
+//
+// Parameters:
+//   - code: The authorization code received from the OIDC provider.
+//   - redirectURL: The redirect URI used in the initial authorization request.
+//   - codeVerifier: The PKCE code verifier stored in the session (if PKCE is enabled).
+//
+// Returns:
+//   - A TokenResponse containing the obtained tokens.
+//   - An error if the code exchange fails.
+func (t *TraefikOidc) exchangeCodeForToken(code string, redirectURL string, codeVerifier string) (*TokenResponse, error) {
 	ctx := context.Background()
-	tokenResponse, err := t.exchangeTokens(ctx, "authorization_code", code, redirectURL)
+
+	// Only include code verifier if PKCE is enabled
+	effectiveCodeVerifier := ""
+	if t.enablePKCE && codeVerifier != "" {
+		effectiveCodeVerifier = codeVerifier
+	}
+
+	tokenResponse, err := t.exchangeTokens(ctx, "authorization_code", code, redirectURL, effectiveCodeVerifier)
 	if err != nil {
 		return nil, fmt.Errorf("failed to exchange code for token: %w", err)
 	}
 	return tokenResponse, nil
 }
 
-// createStringMap creates a map from a slice of strings.
-// Used for efficient lookups in allowed domains and roles.
+// createStringMap converts a slice of strings into a map[string]struct{} (a set).
+// This is useful for creating efficient lookups (O(1) average time complexity)
+// for checking the presence of items like allowed domains, roles, or groups.
+//
+// Parameters:
+//   - keys: A slice of strings to be added to the set.
+//
+// Returns:
+//   - A map where the keys are the strings from the input slice and the values are empty structs.
 func createStringMap(keys []string) map[string]struct{} {
 	result := make(map[string]struct{})
 	for _, key := range keys {
@@ -346,9 +323,17 @@ func createStringMap(keys []string) map[string]struct{} {
 	return result
 }
 
-// handleLogout manages the OIDC logout process.
-// It clears the session and redirects either to the OIDC provider's
-// end session endpoint (if available) or to the configured post-logout URL.
+// handleLogout processes requests to the configured logout path.
+// It performs the following steps:
+//  1. Retrieves the current user session.
+//  2. Gets the access token (ID token hint) from the session.
+//  3. Clears all authentication-related data from the session cookies.
+//  4. Determines the final post-logout redirect URI.
+//  5. If an OIDC end_session_endpoint is configured and an ID token hint is available,
+//     it builds the OIDC logout URL and redirects the user agent to the provider for logout.
+//  6. Otherwise, it redirects the user agent directly to the post-logout redirect URI.
+//
+// It handles potential errors during session retrieval or clearing.
 func (t *TraefikOidc) handleLogout(rw http.ResponseWriter, req *http.Request) {
 	session, err := t.sessionManager.GetSession(req)
 	if err != nil {
@@ -390,11 +375,18 @@ func (t *TraefikOidc) handleLogout(rw http.ResponseWriter, req *http.Request) {
 	http.Redirect(rw, req, postLogoutRedirectURI, http.StatusFound)
 }
 
-// BuildLogoutURL constructs the OIDC end session URL with appropriate parameters.
+// BuildLogoutURL constructs the URL for redirecting the user agent to the OIDC provider's
+// end_session_endpoint, including the required id_token_hint and optional
+// post_logout_redirect_uri parameters as query arguments.
+//
 // Parameters:
-//   - endSessionURL: The OIDC provider's end session endpoint
-//   - idToken: The ID token to be invalidated
-//   - postLogoutRedirectURI: Where to redirect after logout completes
+//   - endSessionURL: The URL of the OIDC provider's end session endpoint.
+//   - idToken: The ID token previously issued to the user (used as id_token_hint).
+//   - postLogoutRedirectURI: The optional URI where the provider should redirect the user agent after logout.
+//
+// Returns:
+//   - The fully constructed logout URL string.
+//   - An error if the provided endSessionURL is invalid.
 func BuildLogoutURL(endSessionURL, idToken, postLogoutRedirectURI string) (string, error) {
 	u, err := url.Parse(endSessionURL)
 	if err != nil {

helpers_test.go

@@ -7,172 +7,12 @@ import (
 	"time"
 )
 
-func TestTokenBlacklistSizeLimit(t *testing.T) {
-	tb := NewTokenBlacklist()
-
-	// Add tokens up to maxSize
-	for i := 0; i < 1000; i++ {
-		tb.Add(fmt.Sprintf("token%d", i), time.Now().Add(time.Hour))
-	}
-
-	// Verify size is at max
-	if tb.Count() != 1000 {
-		t.Errorf("Expected blacklist size to be 1000, got %d", tb.Count())
-	}
-
-	// Add one more token, should trigger cleanup/eviction
-	tb.Add("newtoken", time.Now().Add(time.Hour))
-
-	// Size should still be at max
-	if tb.Count() > 1000 {
-		t.Errorf("Blacklist exceeded max size: %d", tb.Count())
-	}
-}
-
-func TestTokenBlacklistExpiredCleanup(t *testing.T) {
-	tb := NewTokenBlacklist()
-
-	// Add some expired tokens
-	for i := 0; i < 500; i++ {
-		tb.Add(fmt.Sprintf("expired%d", i), time.Now().Add(-time.Hour))
-	}
-
-	// Add some valid tokens
-	for i := 0; i < 500; i++ {
-		tb.Add(fmt.Sprintf("valid%d", i), time.Now().Add(time.Hour))
-	}
-
-	// Force cleanup
-	tb.Cleanup()
-
-	// Only valid tokens should remain
-	if tb.Count() != 500 {
-		t.Errorf("Expected 500 valid tokens after cleanup, got %d", tb.Count())
-	}
-
-	// Verify only valid tokens remain
-	tb.mutex.RLock()
-	defer tb.mutex.RUnlock()
-	for token, expiry := range tb.tokens {
-		if time.Now().After(expiry) {
-			t.Errorf("Found expired token after cleanup: %s", token)
-		}
-	}
-}
-
-func TestTokenBlacklistOldestEviction(t *testing.T) {
-	tb := NewTokenBlacklist()
-
-	// Add tokens at capacity with different expiration times
-	baseTime := time.Now()
-	oldestToken := "oldest"
-
-	// Add oldest token first
-	tb.Add(oldestToken, baseTime.Add(time.Hour))
-
-	// Fill up to capacity with newer tokens
-	for i := 0; i < 999; i++ {
-		tb.Add(fmt.Sprintf("token%d", i), baseTime.Add(time.Hour*2))
-	}
-
-	// Add a new token that should evict the oldest
-	newToken := "newest"
-	tb.Add(newToken, baseTime.Add(time.Hour*3))
-
-	// Verify oldest token was evicted
-	if tb.IsBlacklisted(oldestToken) {
-		t.Error("Oldest token should have been evicted")
-	}
-
-	// Verify newest token is present
-	if !tb.IsBlacklisted(newToken) {
-		t.Error("Newest token should be present")
-	}
-}
-
-func TestTokenBlacklistMemoryUsage(t *testing.T) {
-	tb := NewTokenBlacklist()
-	iterations := 10000
-
-	// Force initial GC
-	runtime.GC()
-
-	// Record initial memory stats
-	var m1, m2 runtime.MemStats
-	runtime.ReadMemStats(&m1)
-
-	// Simulate heavy usage
-	for i := 0; i < iterations; i++ {
-		// Add new token
-		tb.Add(fmt.Sprintf("token%d", i), time.Now().Add(time.Hour))
-
-		// Periodically check blacklisted status
-		if i%100 == 0 {
-			tb.IsBlacklisted(fmt.Sprintf("token%d", i-50))
-		}
-
-		// Periodically cleanup
-		if i%1000 == 0 {
-			tb.Cleanup()
-		}
-	}
-
-	// Force GC and wait for it to complete
-	runtime.GC()
-	time.Sleep(100 * time.Millisecond)
-	runtime.ReadMemStats(&m2)
-
-	// Check memory growth (using HeapAlloc for more accurate measurement)
-	memoryGrowth := int64(m2.HeapAlloc - m1.HeapAlloc)
-	maxAllowedGrowth := int64(2 * 1024 * 1024) // 2MB max growth
-
-	if memoryGrowth > maxAllowedGrowth {
-		t.Logf("Initial HeapAlloc: %d, Final HeapAlloc: %d", m1.HeapAlloc, m2.HeapAlloc)
-		t.Errorf("Excessive memory growth: %d bytes", memoryGrowth)
-	}
-
-	// Verify size stayed within limits
-	if tb.Count() > 1000 {
-		t.Errorf("Blacklist exceeded max size: %d", tb.Count())
-	}
-}
-
-func TestConcurrentTokenBlacklistOperations(t *testing.T) {
-	tb := NewTokenBlacklist()
-	iterations := 1000
-	concurrency := 10
-	done := make(chan bool)
-
-	// Start multiple goroutines performing operations
-	for i := 0; i < concurrency; i++ {
-		go func(id int) {
-			for j := 0; j < iterations; j++ {
-				// Add tokens
-				token := fmt.Sprintf("token%d-%d", id, j)
-				tb.Add(token, time.Now().Add(time.Hour))
-
-				// Check blacklist status
-				tb.IsBlacklisted(token)
-
-				// Periodic cleanup
-				if j%100 == 0 {
-					tb.Cleanup()
-				}
-			}
-			done <- true
-		}(i)
-	}
-
-	// Wait for all goroutines to complete
-	for i := 0; i < concurrency; i++ {
-		<-done
-	}
-
-	// Verify size constraints were maintained
-	if tb.Count() > 1000 {
-		t.Errorf("Blacklist exceeded max size under concurrent operations: %d", tb.Count())
-	}
-}
+// Removed tests related to the old TokenBlacklist implementation:
+// - TestTokenBlacklistSizeLimit
+// - TestTokenBlacklistExpiredCleanup
+// - TestTokenBlacklistOldestEviction
+// - TestTokenBlacklistMemoryUsage
+// - TestConcurrentTokenBlacklistOperations
 
 func TestTokenCacheMemoryUsage(t *testing.T) {
 	tc := NewTokenCache()

jwk.go

@@ -45,6 +45,21 @@ type JWKCacheInterface interface {
 	Cleanup()
 }
 
+// GetJWKS retrieves the JSON Web Key Set (JWKS) from the cache or fetches it from the provider.
+// It first checks if a valid, non-expired JWKS is present in the cache. If so, it returns the cached version.
+// Otherwise, it attempts to fetch the JWKS from the specified jwksURL using the provided httpClient.
+// If the fetch is successful, the JWKS is stored in the cache with an expiration time based on CacheLifetime
+// (defaulting to 1 hour if not set) and returned.
+// This method uses double-checked locking to minimize contention when the cache needs refreshing.
+//
+// Parameters:
+//   - ctx: Context for the HTTP request if fetching is required.
+//   - jwksURL: The URL of the OIDC provider's JWKS endpoint.
+//   - httpClient: The HTTP client to use for fetching the JWKS.
+//
+// Returns:
+//   - A pointer to the JWKSet containing the keys.
+//   - An error if fetching fails or the response cannot be decoded.
 func (c *JWKCache) GetJWKS(ctx context.Context, jwksURL string, httpClient *http.Client) (*JWKSet, error) {
 	c.mutex.RLock()
 	if c.jwks != nil && time.Now().Before(c.expiresAt) {
@@ -74,6 +89,8 @@ func (c *JWKCache) GetJWKS(ctx context.Context, jwksURL string, httpClient *http
 	return jwks, nil
 }
 
+// Cleanup removes the cached JWKS if it has expired.
+// This is intended to be called periodically to ensure stale JWKS data is cleared.
 func (c *JWKCache) Cleanup() {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
@@ -84,6 +101,17 @@ func (c *JWKCache) Cleanup() {
 	}
 }
 
+// fetchJWKS retrieves the JSON Web Key Set (JWKS) from the specified URL.
+// It uses the provided context and HTTP client to make the request.
+//
+// Parameters:
+//   - ctx: Context for the HTTP request.
+//   - jwksURL: The URL of the OIDC provider's JWKS endpoint.
+//   - httpClient: The HTTP client to use for the request.
+//
+// Returns:
+//   - A pointer to the fetched JWKSet.
+//   - An error if the request fails, the status code is not OK, or the response body cannot be decoded.
 func fetchJWKS(ctx context.Context, jwksURL string, httpClient *http.Client) (*JWKSet, error) {
 	// Create a request with context to enforce timeout
 	req, err := http.NewRequestWithContext(ctx, "GET", jwksURL, nil)
@@ -109,6 +137,16 @@ func fetchJWKS(ctx context.Context, jwksURL string, httpClient *http.Client) (*J
 	return &jwks, nil
 }
 
+// jwkToPEM converts a JWK (JSON Web Key) object into PEM (Privacy-Enhanced Mail) format.
+// It selects the appropriate conversion function based on the JWK's key type ("kty").
+// Currently supports "RSA" and "EC" key types.
+//
+// Parameters:
+//   - jwk: A pointer to the JWK object to convert.
+//
+// Returns:
+//   - A byte slice containing the public key in PEM format.
+//   - An error if the key type is unsupported or conversion fails.
 func jwkToPEM(jwk *JWK) ([]byte, error) {
 	converter, ok := jwkConverters[jwk.Kty]
 	if !ok {
@@ -124,6 +162,17 @@ var jwkConverters = map[string]jwkToPEMConverter{
 	"EC":  ecJWKToPEM,
 }
 
+// rsaJWKToPEM converts an RSA JWK into PEM format.
+// It decodes the modulus (n) and exponent (e) from base64 URL encoding,
+// constructs an rsa.PublicKey, marshals it into PKIX format, and then
+// encodes it as a PEM block.
+//
+// Parameters:
+//   - jwk: A pointer to the RSA JWK object (must have "kty": "RSA").
+//
+// Returns:
+//   - A byte slice containing the RSA public key in PEM format.
+//   - An error if decoding parameters fails or key marshaling fails.
 func rsaJWKToPEM(jwk *JWK) ([]byte, error) {
 	nBytes, err := base64.RawURLEncoding.DecodeString(jwk.N)
 	if err != nil {
@@ -155,6 +204,18 @@ func rsaJWKToPEM(jwk *JWK) ([]byte, error) {
 	return pubKeyPEM, nil
 }
 
+// ecJWKToPEM converts an EC (Elliptic Curve) JWK into PEM format.
+// It decodes the X and Y coordinates from base64 URL encoding, determines the
+// elliptic curve based on the "crv" parameter (P-256, P-384, P-521),
+// constructs an ecdsa.PublicKey, marshals it into PKIX format, and then
+// encodes it as a PEM block.
+//
+// Parameters:
+//   - jwk: A pointer to the EC JWK object (must have "kty": "EC").
+//
+// Returns:
+//   - A byte slice containing the EC public key in PEM format.
+//   - An error if decoding parameters fails, the curve is unsupported, or key marshaling fails.
 func ecJWKToPEM(jwk *JWK) ([]byte, error) {
 	xBytes, err := base64.RawURLEncoding.DecodeString(jwk.X)
 	if err != nil {

jwt.go

@@ -15,9 +15,15 @@ import (
 	"time"
 )
 
-var replayCacheMu sync.Mutex
-var replayCache = make(map[string]time.Time)
+var (
+	replayCacheMu sync.Mutex
+	replayCache   = make(map[string]time.Time)
+)
 
+// cleanupReplayCache iterates through the replay cache and removes entries
+// whose expiration time is before the current time. This function should be
+// called periodically to prevent the cache from growing indefinitely.
+// It acquires a mutex to ensure thread safety during cleanup.
 func cleanupReplayCache() {
 	now := time.Now()
 	for token, expiry := range replayCache {
@@ -27,8 +33,16 @@ func cleanupReplayCache() {
 	}
 }
 
-// ClockSkewTolerance is configurable to adjust time-based validations.
-var ClockSkewTolerance = 2 * time.Minute
+// ClockSkewToleranceFuture defines the tolerance for future-based claims like 'exp'.
+// Allows for more leniency with expiration checks.
+var ClockSkewToleranceFuture = 2 * time.Minute
+
+// ClockSkewTolerancePast defines the tolerance for past-based claims like 'iat' and 'nbf'.
+// A smaller tolerance is typically used here to prevent accepting tokens issued too far in the future.
+var (
+	ClockSkewTolerancePast = 10 * time.Second
+	ClockSkewTolerance     = 2 * time.Minute
+)
 
 // JWT represents a JSON Web Token as defined in RFC 7519.
 type JWT struct {
@@ -38,7 +52,18 @@ type JWT struct {
 	Token     string
 }
 
-// parseJWT parses a JWT token string into a JWT struct.
+// parseJWT decodes a raw JWT string into its constituent parts: header, claims, and signature.
+// It splits the token string by '.', decodes each part using base64 URL decoding,
+// and unmarshals the header and claims JSON into maps. The raw signature bytes are stored.
+// It performs basic format validation (expecting 3 parts).
+// Note: This function does *not* validate the signature or the claims.
+//
+// Parameters:
+//   - tokenString: The raw JWT string.
+//
+// Returns:
+//   - A pointer to a JWT struct containing the decoded parts.
+//   - An error if the token format is invalid or decoding/unmarshaling fails.
 func parseJWT(tokenString string) (*JWT, error) {
 	parts := strings.Split(tokenString, ".")
 	if len(parts) != 3 {
@@ -74,8 +99,24 @@ func parseJWT(tokenString string) (*JWT, error) {
 	return jwt, nil
 }
 
-// Verify validates the standard JWT claims as defined in RFC 7519.
-// Verify validates the standard JWT claims as defined in RFC 7519.
+// Verify performs standard claim validation on the JWT according to RFC 7519.
+// It checks the following:
+// - Algorithm ('alg') is supported.
+// - Issuer ('iss') matches the expected issuerURL.
+// - Audience ('aud') contains the expected clientID.
+// - Expiration time ('exp') is in the future (within tolerance).
+// - Issued at time ('iat') is in the past (within tolerance).
+// - Not before time ('nbf'), if present, is in the past (within tolerance).
+// - Subject ('sub') claim exists and is not empty.
+// - JWT ID ('jti'), if present, is checked against a replay cache to prevent token reuse.
+//
+// Parameters:
+//   - issuerURL: The expected issuer URL (e.g., "https://accounts.google.com").
+//   - clientID: The expected audience value (the client ID of this application).
+//
+// Returns:
+//   - nil if all standard claims are valid.
+//   - An error describing the first validation failure encountered.
 func (j *JWT) Verify(issuerURL, clientID string) error {
 	// Validate algorithm to prevent algorithm switching attacks
 	alg, ok := j.Header["alg"].(string)
@@ -164,6 +205,17 @@ func (j *JWT) Verify(issuerURL, clientID string) error {
 
 	return nil
 }
+
+// verifyAudience checks if the expected audience is present in the token's 'aud' claim.
+// The 'aud' claim can be a single string or an array of strings.
+//
+// Parameters:
+//   - tokenAudience: The 'aud' claim value extracted from the token (can be string or []interface{}).
+//   - expectedAudience: The audience value expected for this application (client ID).
+//
+// Returns:
+//   - nil if the expected audience is found.
+//   - An error if the claim type is invalid or the expected audience is not present.
 func verifyAudience(tokenAudience interface{}, expectedAudience string) error {
 	switch aud := tokenAudience.(type) {
 	case string:
@@ -187,6 +239,15 @@ func verifyAudience(tokenAudience interface{}, expectedAudience string) error {
 	return nil
 }
 
+// verifyIssuer checks if the token's 'iss' claim matches the expected issuer URL.
+//
+// Parameters:
+//   - tokenIssuer: The 'iss' claim value from the token.
+//   - expectedIssuer: The expected issuer URL configured for the OIDC provider.
+//
+// Returns:
+//   - nil if the issuers match.
+//   - An error if the issuers do not match.
 func verifyIssuer(tokenIssuer, expectedIssuer string) error {
 	if tokenIssuer != expectedIssuer {
 		return fmt.Errorf("invalid issuer (token: %s, expected: %s)", tokenIssuer, expectedIssuer)
@@ -194,54 +255,76 @@ func verifyIssuer(tokenIssuer, expectedIssuer string) error {
 	return nil
 }
 
-// verifyTimeConstraint is a generic function to verify time-based claims
+// verifyTimeConstraint checks time-based claims ('exp', 'iat', 'nbf') against the current time,
+// allowing for configurable clock skew. It uses different tolerances for past and future checks.
+//
+// Parameters:
+//   - unixTime: The timestamp value from the claim (as a float64 Unix time).
+//   - claimName: The name of the claim being verified ("exp", "iat", "nbf").
+//   - future: A boolean indicating the direction of the check (true for 'exp', false for 'iat'/'nbf').
+//
+// Returns:
+//   - nil if the time constraint is met within the allowed tolerance.
+//   - An error describing the failure (e.g., "token has expired", "token used before issued").
 func verifyTimeConstraint(unixTime float64, claimName string, future bool) error {
 	claimTime := time.Unix(int64(unixTime), 0)
-	now := time.Now().Truncate(time.Second)
+	now := time.Now() // Use current time without truncation
 
-	// For expiration (future=true), we add skew to now (making now later)
-	// For iat/nbf (future=false), we subtract skew from now (making now earlier)
-	skewDirection := 1
-	if !future {
-		skewDirection = -1
-	}
-	skewedNow := now.Add(time.Duration(skewDirection) * ClockSkewTolerance)
-
-	if claimTime.Equal(now) {
-		return nil
-	}
-
-	// For expiration: if skewedNow (later) is after expiration, token expired
-	// For iat/nbf: if skewedNow (earlier) is before claim time, token not yet valid
-	if (future && skewedNow.After(claimTime)) || (!future && skewedNow.Before(claimTime)) {
-		var reason string
-		if future {
-			reason = "has expired"
-		} else {
+	var err error
+	if future { // 'exp' check
+		// Token is expired if Now is after (ClaimTime + FutureTolerance)
+		allowedExpiry := claimTime.Add(ClockSkewToleranceFuture)
+		if now.After(allowedExpiry) {
+			err = fmt.Errorf("token has expired (exp: %v, now: %v, allowed_until: %v)", claimTime.UTC(), now.UTC(), allowedExpiry.UTC())
+		}
+	} else { // 'iat' or 'nbf' check
+		// Token is invalid if Now is before (ClaimTime - PastTolerance)
+		allowedStart := claimTime.Add(-ClockSkewTolerancePast)
+		if now.Before(allowedStart) {
+			reason := "not yet valid"
 			if claimName == "iat" {
 				reason = "used before issued"
-			} else {
-				reason = "not yet valid"
 			}
+			err = fmt.Errorf("token %s (%s: %v, now: %v, allowed_from: %v)", reason, claimName, claimTime.UTC(), now.UTC(), allowedStart.UTC())
 		}
-		return fmt.Errorf("token %s (%s: %v, now: %v)", reason, claimName, claimTime.UTC(), now.UTC())
 	}
 
-	return nil
+	return err
 }
 
+// verifyExpiration checks the 'exp' (Expiration Time) claim.
+// It calls verifyTimeConstraint with future=true.
 func verifyExpiration(expiration float64) error {
 	return verifyTimeConstraint(expiration, "exp", true)
 }
 
+// verifyIssuedAt checks the 'iat' (Issued At) claim.
+// It calls verifyTimeConstraint with future=false.
 func verifyIssuedAt(issuedAt float64) error {
 	return verifyTimeConstraint(issuedAt, "iat", false)
 }
 
+// verifyNotBefore checks the 'nbf' (Not Before) claim.
+// It calls verifyTimeConstraint with future=false.
 func verifyNotBefore(notBefore float64) error {
 	return verifyTimeConstraint(notBefore, "nbf", false)
 }
 
+// verifySignature validates the JWT's signature using the provided public key.
+// It parses the public key from PEM format, selects the appropriate hashing algorithm
+// based on the 'alg' parameter (SHA256/384/512), hashes the token's signing input
+// (header + "." + payload), and then verifies the signature against the hash using
+// the corresponding RSA (PKCS1v15 or PSS) or ECDSA verification method.
+//
+// Parameters:
+//   - tokenString: The raw, complete JWT string.
+//   - publicKeyPEM: The public key corresponding to the private key used for signing, in PEM format.
+//   - alg: The algorithm specified in the JWT header (e.g., "RS256", "ES384").
+//
+// Returns:
+//   - nil if the signature is valid.
+//   - An error if the token format is invalid, decoding fails, key parsing fails,
+//     the algorithm is unsupported, or the signature verification fails.
 func verifySignature(tokenString string, publicKeyPEM []byte, alg string) error {
 	parts := strings.Split(tokenString, ".")
 	if len(parts) != 3 {

metadata_cache.go

@@ -15,6 +15,8 @@ type MetadataCache struct {
 	stopCleanup         chan struct{}
 }
 
+// NewMetadataCache creates a new MetadataCache instance.
+// It initializes the cache structure and starts the background cleanup goroutine.
 func NewMetadataCache() *MetadataCache {
 	c := &MetadataCache{
 		autoCleanupInterval: 5 * time.Minute,
@@ -24,7 +26,8 @@ func NewMetadataCache() *MetadataCache {
 	return c
 }
 
-// Cleanup removes expired metadata from the cache.
+// Cleanup removes the cached provider metadata if it has expired.
+// This is called periodically by the auto-cleanup goroutine.
 func (c *MetadataCache) Cleanup() {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
@@ -34,11 +37,32 @@ func (c *MetadataCache) Cleanup() {
 		c.metadata = nil
 	}
 }
+
+// isCacheValid checks if the cached metadata is present and has not expired.
+// Note: This function assumes the read lock is held or it's called from a context
+// where the lock is already held (like within GetMetadata after locking).
 func (c *MetadataCache) isCacheValid() bool {
 	return c.metadata != nil && time.Now().Before(c.expiresAt)
 }
 
-// GetMetadata retrieves the metadata from cache or fetches it if expired
+// GetMetadata retrieves the OIDC provider metadata.
+// It first checks the cache for valid, non-expired metadata. If found, it's returned immediately.
+// If the cache is empty or expired, it attempts to fetch the metadata from the provider's
+// well-known endpoint using discoverProviderMetadata.
+// If fetching is successful, the new metadata is cached for 1 hour.
+// If fetching fails but valid metadata exists in the cache (even if expired), the cache expiry
+// is extended by 5 minutes, and the cached data is returned to prevent thundering herd issues.
+// If fetching fails and there's no cached data, an error is returned.
+// It employs double-checked locking for thread safety and performance.
+//
+// Parameters:
+//   - providerURL: The base URL of the OIDC provider.
+//   - httpClient: The HTTP client to use for fetching metadata.
+//   - logger: The logger instance for recording errors or warnings.
+//
+// Returns:
+//   - A pointer to the ProviderMetadata struct.
+//   - An error if metadata cannot be retrieved from cache or fetched from the provider.
 func (c *MetadataCache) GetMetadata(providerURL string, httpClient *http.Client, logger *Logger) (*ProviderMetadata, error) {
 	c.mutex.RLock()
 	if c.isCacheValid() {
@@ -67,24 +91,21 @@ func (c *MetadataCache) GetMetadata(providerURL string, httpClient *http.Client,
 	}
 
 	c.metadata = metadata
-	// Calculate expiration time based on usage patterns
-	usageCount := 0 // This should be replaced with actual usage tracking logic
-	if usageCount < 10 {
-		c.expiresAt = time.Now().Add(30 * time.Minute)
-	} else if usageCount < 50 {
-		c.expiresAt = time.Now().Add(1 * time.Hour)
-	} else {
-		c.expiresAt = time.Now().Add(2 * time.Hour)
-	}
+	// Set a fixed cache lifetime (e.g., 1 hour)
+	// TODO: Consider making this configurable or respecting HTTP cache headers
+	c.expiresAt = time.Now().Add(1 * time.Hour)
 
 	// End of GetMetadata
 	return metadata, nil
 }
 
+// startAutoCleanup starts the background goroutine that periodically calls Cleanup
+// to remove expired metadata from the cache.
 func (c *MetadataCache) startAutoCleanup() {
 	autoCleanupRoutine(c.autoCleanupInterval, c.stopCleanup, c.Cleanup)
 }
 
+// Close stops the automatic cleanup goroutine associated with this metadata cache.
 func (c *MetadataCache) Close() {
 	close(c.stopCleanup)
 }

session.go

@@ -16,8 +16,15 @@ import (
 	"github.com/gorilla/sessions"
 )
 
-// generateSecureRandomString creates a cryptographically secure random string of specified length.
-// It returns the generated string or an error if random generation fails.
+// generateSecureRandomString creates a cryptographically secure, hex-encoded random string.
+// It reads the specified number of bytes from crypto/rand and encodes them as a hexadecimal string.
+//
+// Parameters:
+//   - length: The number of random bytes to generate (the resulting hex string will be twice this length).
+//
+// Returns:
+//   - A hex-encoded random string.
+//   - An error if reading random bytes fails.
 func generateSecureRandomString(length int) (string, error) {
 	bytes := make([]byte, length)
 	if _, err := rand.Read(bytes); err != nil {
@@ -56,7 +63,14 @@ const (
 	minEncryptionKeyLength = 32
 )
 
-// compressToken compresses a token using gzip and base64 encodes it.
+// compressToken compresses the input string using gzip and then encodes the result using standard base64 encoding.
+// If any error occurs during compression, it returns the original uncompressed token as a fallback.
+//
+// Parameters:
+//   - token: The string to compress.
+//
+// Returns:
+//   - The base64 encoded, gzipped string, or the original string if compression fails.
 func compressToken(token string) string {
 	var b bytes.Buffer
 	gz := gzip.NewWriter(&b)
@@ -69,7 +83,15 @@ func compressToken(token string) string {
 	return base64.StdEncoding.EncodeToString(b.Bytes())
 }
 
-// decompressToken decompresses a base64 encoded gzipped token.
+// decompressToken decodes a standard base64 encoded string and then decompresses the result using gzip.
+// If base64 decoding or gzip decompression fails, it returns the original input string as a fallback,
+// assuming it might not have been compressed.
+//
+// Parameters:
+//   - compressed: The base64 encoded, gzipped string.
+//
+// Returns:
+//   - The decompressed original string, or the input string if decompression fails.
 func decompressToken(compressed string) string {
 	data, err := base64.StdEncoding.DecodeString(compressed)
 	if err != nil {
@@ -128,25 +150,27 @@ func NewSessionManager(encryptionKey string, forceHTTPS bool, logger *Logger) (*
 
 	// Initialize session pool.
 	sm.sessionPool.New = func() interface{} {
+		// Initialize SessionData with necessary fields and the mutex.
 		return &SessionData{
 			manager:            sm,
 			accessTokenChunks:  make(map[int]*sessions.Session),
 			refreshTokenChunks: make(map[int]*sessions.Session),
+			refreshMutex:       sync.Mutex{}, // Initialize the mutex
 		}
 	}
 
 	return sm, nil
 }
 
-// getSessionOptions returns secure session options configured for the current request.
-// Parameters:
-//   - isSecure: Whether the current request is using HTTPS.
+// getSessionOptions returns a sessions.Options struct configured with security best practices.
+// It sets HttpOnly to true, Secure based on the request scheme or forceHTTPS setting,
+// SameSite to LaxMode, MaxAge to the absoluteSessionTimeout, and Path to "/".
 //
-// The options ensure cookies are:
-//   - HTTP-only (not accessible via JavaScript)
-//   - Secure when using HTTPS or when forceHTTPS is enabled
-//   - Using SameSite=Lax for CSRF protection
-//   - Set with appropriate timeout and path settings
+// Parameters:
+//   - isSecure: A boolean indicating if the current request context is secure (HTTPS).
+//
+// Returns:
+//   - A pointer to a configured sessions.Options struct.
 func (sm *SessionManager) getSessionOptions(isSecure bool) *sessions.Options {
 	return &sessions.Options{
 		HttpOnly: true,
@@ -208,11 +232,14 @@ func (sm *SessionManager) GetSession(r *http.Request) (*SessionData, error) {
 	return sessionData, nil
 }
 
-// getTokenChunkSessions retrieves all session chunks for a given token type.
+// getTokenChunkSessions retrieves all cookie chunks associated with a large token (access or refresh).
+// It iteratively attempts to load cookies named "{baseName}_0", "{baseName}_1", etc., until
+// a cookie is not found or returns an error. The loaded sessions are stored in the provided chunks map.
+//
 // Parameters:
-//   - r: The HTTP request
-//   - baseName: The base name for the token's session cookies
-//   - chunks: Map to store the chunks in
+//   - r: The incoming HTTP request containing the cookies.
+//   - baseName: The base name of the cookie (e.g., accessTokenCookie).
+//   - 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++ {
 		sessionName := fmt.Sprintf("%s_%d", baseName, i)
@@ -251,12 +278,21 @@ type SessionData struct {
 	// refreshTokenChunks stores additional chunks of the refresh token
 	// when it exceeds the maximum cookie size.
 	refreshTokenChunks map[int]*sessions.Session
+
+	// refreshMutex protects refresh token operations within this session instance.
+	refreshMutex sync.Mutex
 }
 
-// Save persists all session data to cookies in the HTTP response.
-// It saves the main session, token sessions, and any token chunks,
-// applying appropriate security options to each cookie. All cookies
-// are saved with consistent security settings based on the request scheme.
+// Save persists all parts of the session (main, access token, refresh token, and any chunks)
+// back to the client as cookies in the HTTP response. It applies secure cookie options
+// obtained via getSessionOptions based on the request's security context.
+//
+// Parameters:
+//   - r: The original HTTP request (used to determine security context for cookie options).
+//   - w: The HTTP response writer to which the Set-Cookie headers will be added.
+//
+// Returns:
+//   - An error if saving any of the session components fails.
 func (sd *SessionData) Save(r *http.Request, w http.ResponseWriter) error {
 	isSecure := strings.HasPrefix(r.URL.Scheme, "https") || sd.manager.forceHTTPS
 
@@ -300,7 +336,19 @@ func (sd *SessionData) Save(r *http.Request, w http.ResponseWriter) error {
 	return nil
 }
 
-// Clear removes all session data by expiring all cookies and clearing their values.
+// Clear removes all session data associated with this SessionData instance.
+// It clears the values map of the main, access, and refresh sessions, sets their MaxAge to -1
+// to expire the cookies immediately, and clears any associated token chunk cookies.
+// If a ResponseWriter is provided, it attempts to save the expired sessions to send the
+// expiring Set-Cookie headers. Finally, it clears internal fields and returns the SessionData
+// object to the pool.
+//
+// Parameters:
+//   - r: The HTTP request (required by the underlying session store).
+//   - w: The HTTP response writer (optional). If provided, expiring Set-Cookie headers will be sent.
+//
+// Returns:
+//   - An error if saving the expired sessions fails (only if w is not nil).
 func (sd *SessionData) Clear(r *http.Request, w http.ResponseWriter) error {
 	// Clear and expire all sessions.
 	sd.mainSession.Options.MaxAge = -1
@@ -335,7 +383,12 @@ func (sd *SessionData) Clear(r *http.Request, w http.ResponseWriter) error {
 	return err
 }
 
-// clearTokenChunks removes all session chunks for a given token type.
+// clearTokenChunks iterates through a map of session chunks, clears their values,
+// and sets their MaxAge to -1 to expire them. This is used internally by Clear.
+//
+// Parameters:
+//   - r: The HTTP request (required by the underlying session store, though not directly used here).
+//   - chunks: The map of session chunks (e.g., sd.accessTokenChunks) to clear and expire.
 func (sd *SessionData) clearTokenChunks(r *http.Request, chunks map[int]*sessions.Session) {
 	for _, session := range chunks {
 		session.Options.MaxAge = -1
@@ -345,7 +398,12 @@ func (sd *SessionData) clearTokenChunks(r *http.Request, chunks map[int]*session
 	}
 }
 
-// GetAuthenticated returns whether the current session is authenticated.
+// GetAuthenticated checks if the session is marked as authenticated and has not exceeded
+// the absolute session timeout.
+//
+// Returns:
+//   - true if the "authenticated" flag is set to true and the session creation time is within the allowed timeout.
+//   - false otherwise.
 func (sd *SessionData) GetAuthenticated() bool {
 	auth, _ := sd.mainSession.Values["authenticated"].(bool)
 	if !auth {
@@ -360,8 +418,15 @@ func (sd *SessionData) GetAuthenticated() bool {
 	return time.Since(time.Unix(createdAt, 0)) <= absoluteSessionTimeout
 }
 
-// SetAuthenticated updates the session's authentication status and rotates session ID.
-// Returns an error if generating a new session ID fails.
+// SetAuthenticated sets the authentication status of the session.
+// If setting to true, it generates a new secure session ID for the main session
+// to prevent session fixation attacks and records the current time as the creation time.
+//
+// Parameters:
+//   - value: The boolean authentication status (true for authenticated, false otherwise).
+//
+// Returns:
+//   - An error if generating a new session ID fails when setting value to true.
 func (sd *SessionData) SetAuthenticated(value bool) error {
 	if value {
 		id, err := generateSecureRandomString(32)
@@ -375,7 +440,12 @@ func (sd *SessionData) SetAuthenticated(value bool) error {
 	return nil
 }
 
-// GetAccessToken retrieves the complete access token from the session.
+// GetAccessToken retrieves the access token stored in the session.
+// It handles reassembling the token from multiple cookie chunks if necessary
+// and decompresses it if it was stored compressed.
+//
+// Returns:
+//   - The complete, decompressed access token string, or an empty string if not found.
 func (sd *SessionData) GetAccessToken() string {
 	token, _ := sd.accessSession.Values["token"].(string)
 	if token != "" {
@@ -409,7 +479,14 @@ func (sd *SessionData) GetAccessToken() string {
 	return token
 }
 
-// SetAccessToken stores the access token in the session.
+// SetAccessToken stores the provided access token in the session.
+// It first expires any existing access token chunk cookies.
+// It then compresses the token. If the compressed token fits within a single cookie (maxCookieSize),
+// it's stored directly in the primary access token session. Otherwise, the compressed token
+// is split into chunks, and each chunk is stored in a separate numbered cookie (_oidc_raczylo_a_0, _oidc_raczylo_a_1, etc.).
+//
+// Parameters:
+//   - token: The access token string to store.
 func (sd *SessionData) SetAccessToken(token string) {
 	// Expire any existing chunk cookies first.
 	if sd.request != nil {
@@ -439,7 +516,12 @@ func (sd *SessionData) SetAccessToken(token string) {
 	}
 }
 
-// GetRefreshToken retrieves the complete refresh token from the session.
+// GetRefreshToken retrieves the refresh token stored in the session.
+// It handles reassembling the token from multiple cookie chunks if necessary
+// and decompresses it if it was stored compressed.
+//
+// Returns:
+//   - The complete, decompressed refresh token string, or an empty string if not found.
 func (sd *SessionData) GetRefreshToken() string {
 	token, _ := sd.refreshSession.Values["token"].(string)
 	if token != "" {
@@ -473,7 +555,14 @@ func (sd *SessionData) GetRefreshToken() string {
 	return token
 }
 
-// SetRefreshToken stores the refresh token in the session.
+// SetRefreshToken stores the provided refresh token in the session.
+// It first expires any existing refresh token chunk cookies.
+// It then compresses the token. If the compressed token fits within a single cookie (maxCookieSize),
+// it's stored directly in the primary refresh token session. Otherwise, the compressed token
+// is split into chunks, and each chunk is stored in a separate numbered cookie (_oidc_raczylo_r_0, _oidc_raczylo_r_1, etc.).
+//
+// Parameters:
+//   - token: The refresh token string to store.
 func (sd *SessionData) SetRefreshToken(token string) {
 	// Expire any existing chunk cookies first.
 	if sd.request != nil {
@@ -503,7 +592,13 @@ func (sd *SessionData) SetRefreshToken(token string) {
 	}
 }
 
-// expireAccessTokenChunks expires any existing access token chunk cookies.
+// expireAccessTokenChunks finds all existing access token chunk cookies (_oidc_raczylo_a_N)
+// associated with the current request, clears their values, and sets their MaxAge to -1.
+// If a ResponseWriter is provided, it attempts to save the expired chunk sessions to send
+// the expiring Set-Cookie headers. This is used internally when setting a new access token.
+//
+// Parameters:
+//   - w: The HTTP response writer (optional). If provided, expiring Set-Cookie headers will be sent.
 func (sd *SessionData) expireAccessTokenChunks(w http.ResponseWriter) {
 	for i := 0; ; i++ {
 		sessionName := fmt.Sprintf("%s_%d", accessTokenCookie, i)
@@ -521,7 +616,13 @@ func (sd *SessionData) expireAccessTokenChunks(w http.ResponseWriter) {
 	}
 }
 
-// expireRefreshTokenChunks expires any existing refresh token chunk cookies.
+// expireRefreshTokenChunks finds all existing refresh token chunk cookies (_oidc_raczylo_r_N)
+// associated with the current request, clears their values, and sets their MaxAge to -1.
+// If a ResponseWriter is provided, it attempts to save the expired chunk sessions to send
+// the expiring Set-Cookie headers. This is used internally when setting a new refresh token.
+//
+// Parameters:
+//   - w: The HTTP response writer (optional). If provided, expiring Set-Cookie headers will be sent.
 func (sd *SessionData) expireRefreshTokenChunks(w http.ResponseWriter) {
 	for i := 0; ; i++ {
 		sessionName := fmt.Sprintf("%s_%d", refreshTokenCookie, i)
@@ -539,7 +640,15 @@ func (sd *SessionData) expireRefreshTokenChunks(w http.ResponseWriter) {
 	}
 }
 
-// splitIntoChunks splits a string into chunks of specified size.
+// splitIntoChunks divides a string `s` into a slice of strings, where each element
+// has a maximum length of `chunkSize`.
+//
+// Parameters:
+//   - s: The string to split.
+//   - chunkSize: The maximum size of each chunk.
+//
+// Returns:
+//   - A slice of strings representing the chunks.
 func splitIntoChunks(s string, chunkSize int) []string {
 	var chunks []string
 	for len(s) > 0 {
@@ -554,46 +663,97 @@ func splitIntoChunks(s string, chunkSize int) []string {
 	return chunks
 }
 
-// GetCSRF retrieves the CSRF token from the session.
+// GetCSRF retrieves the Cross-Site Request Forgery (CSRF) token stored in the main session.
+//
+// Returns:
+//   - The CSRF token string, or an empty string if not set.
 func (sd *SessionData) GetCSRF() string {
 	csrf, _ := sd.mainSession.Values["csrf"].(string)
 	return csrf
 }
 
-// SetCSRF stores a new CSRF token in the session.
+// SetCSRF stores the provided CSRF token string in the main session.
+// This token is typically generated at the start of the authentication flow.
+//
+// Parameters:
+//   - token: The CSRF token to store.
 func (sd *SessionData) SetCSRF(token string) {
 	sd.mainSession.Values["csrf"] = token
 }
 
-// GetNonce retrieves the nonce value from the session.
+// GetNonce retrieves the OIDC nonce value stored in the main session.
+// The nonce is used to associate an ID token with the specific authentication request.
+//
+// Returns:
+//   - The nonce string, or an empty string if not set.
 func (sd *SessionData) GetNonce() string {
 	nonce, _ := sd.mainSession.Values["nonce"].(string)
 	return nonce
 }
 
-// SetNonce stores a new nonce value in the session.
+// SetNonce stores the provided OIDC nonce string in the main session.
+// This nonce is typically generated at the start of the authentication flow.
+//
+// Parameters:
+//   - nonce: The nonce string to store.
 func (sd *SessionData) SetNonce(nonce string) {
 	sd.mainSession.Values["nonce"] = nonce
 }
 
-// GetEmail retrieves the authenticated user's email address from the session.
+// GetCodeVerifier retrieves the PKCE (Proof Key for Code Exchange) code verifier
+// stored in the main session. This is only relevant if PKCE is enabled.
+//
+// Returns:
+//   - The code verifier string, or an empty string if not set or PKCE is disabled.
+func (sd *SessionData) GetCodeVerifier() string {
+	codeVerifier, _ := sd.mainSession.Values["code_verifier"].(string)
+	return codeVerifier
+}
+
+// SetCodeVerifier stores the provided PKCE code verifier string in the main session.
+// This is typically called at the start of the authentication flow if PKCE is enabled.
+//
+// Parameters:
+//   - codeVerifier: The PKCE code verifier string to store.
+func (sd *SessionData) SetCodeVerifier(codeVerifier string) {
+	sd.mainSession.Values["code_verifier"] = codeVerifier
+}
+
+// GetEmail retrieves the authenticated user's email address stored in the main session.
+// This is typically extracted from the ID token claims after successful authentication.
+//
+// Returns:
+//   - The user's email address string, or an empty string if not set.
 func (sd *SessionData) GetEmail() string {
 	email, _ := sd.mainSession.Values["email"].(string)
 	return email
 }
 
-// SetEmail stores the user's email address in the session.
+// SetEmail stores the provided user email address string in the main session.
+// This is typically called after successful authentication and claim extraction.
+//
+// Parameters:
+//   - email: The user's email address to store.
 func (sd *SessionData) SetEmail(email string) {
 	sd.mainSession.Values["email"] = email
 }
 
-// GetIncomingPath retrieves the original request path that triggered the authentication flow.
+// GetIncomingPath retrieves the original request URI (including query parameters)
+// that the user was trying to access before being redirected for authentication.
+// This is stored in the main session to allow redirection back after successful login.
+//
+// Returns:
+//   - The original request URI string, or an empty string if not set.
 func (sd *SessionData) GetIncomingPath() string {
 	path, _ := sd.mainSession.Values["incoming_path"].(string)
 	return path
 }
 
-// SetIncomingPath stores the original request path that triggered the authentication flow.
+// SetIncomingPath stores the original request URI (path and query parameters)
+// in the main session. This is typically called at the start of the authentication flow.
+//
+// Parameters:
+//   - path: The original request URI string (e.g., "/protected/resource?id=123").
 func (sd *SessionData) SetIncomingPath(path string) {
 	sd.mainSession.Values["incoming_path"] = path
 }

session_test.go

@@ -1,7 +1,9 @@
 package traefikoidc
 
 import (
-	"math/rand"
+	"crypto/rand"
+	"fmt"
+	"math/big"
 	"net/http/httptest"
 	"strings"
 	"testing"
@@ -12,7 +14,12 @@ func generateRandomString(length int) string {
 	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
 	b := make([]byte, length)
 	for i := range b {
-		b[i] = charset[rand.Intn(len(charset))]
+		num, err := rand.Int(rand.Reader, big.NewInt(int64(len(charset))))
+		if err != nil {
+			// Handle error appropriately in a real application, maybe panic in test helper
+			panic(fmt.Sprintf("crypto/rand failed: %v", err))
+		}
+		b[i] = charset[num.Int64()]
 	}
 	return string(b)
 }

settings.go

@@ -22,6 +22,11 @@ type Config struct {
 	// If not provided, it will be discovered from provider metadata
 	RevocationURL string `json:"revocationURL"`
 
+	// EnablePKCE enables Proof Key for Code Exchange (PKCE) for the authorization code flow (optional)
+	// This enhances security but might not be supported by all OIDC providers
+	// Default: false
+	EnablePKCE bool `json:"enablePKCE"`
+
 	// CallbackURL is the path where the OIDC provider will redirect after authentication (required)
 	// Example: /oauth2/callback
 	CallbackURL string `json:"callbackURL"`
@@ -79,6 +84,11 @@ type Config struct {
 
 	// HTTPClient allows customizing the HTTP client used for OIDC operations (optional)
 	HTTPClient *http.Client
+
+	// RefreshGracePeriodSeconds defines how many seconds before a token expires
+	// the plugin should attempt to refresh it proactively (optional)
+	// Default: 60
+	RefreshGracePeriodSeconds int `json:"refreshGracePeriodSeconds"`
 }
 
 const (
@@ -103,20 +113,36 @@ const (
 //   - RateLimit: 100 requests per second
 //   - PostLogoutRedirectURI: "/"
 //   - ForceHTTPS: true (for security)
+//   - EnablePKCE: false (PKCE is opt-in)
+//
+// CreateConfig initializes a new Config struct with default values for optional fields.
+// It sets default scopes, log level, rate limit, enables ForceHTTPS, and sets the
+// default refresh grace period. Required fields like ProviderURL, ClientID, ClientSecret,
+// CallbackURL, and SessionEncryptionKey must be set explicitly after creation.
+//
+// Returns:
+//   - A pointer to a new Config struct with default settings applied.
 func CreateConfig() *Config {
 	c := &Config{
-		Scopes:     []string{"openid", "profile", "email"},
-		LogLevel:   DefaultLogLevel,
-		RateLimit:  DefaultRateLimit,
-		ForceHTTPS: true, // Secure by default
+		Scopes:                    []string{"openid", "profile", "email"},
+		LogLevel:                  DefaultLogLevel,
+		RateLimit:                 DefaultRateLimit,
+		ForceHTTPS:                true,  // Secure by default
+		EnablePKCE:                false, // PKCE is opt-in
+		RefreshGracePeriodSeconds: 60,    // Default grace period of 60 seconds
 	}
 
 	return c
 }
 
-// Validate performs validation checks on the Config.
-// It ensures all required fields are set and have valid values.
-// Returns an error if any validation check fails.
+// Validate checks the configuration settings for validity.
+// It ensures that required fields (ProviderURL, CallbackURL, ClientID, ClientSecret, SessionEncryptionKey)
+// are present and that URLs are well-formed (HTTPS where required). It also validates
+// the session key length, log level, rate limit, and refresh grace period.
+//
+// Returns:
+//   - nil if the configuration is valid.
+//   - An error describing the first validation failure encountered.
 func (c *Config) Validate() error {
 	// Validate provider URL
 	if c.ProviderURL == "" {
@@ -190,16 +216,34 @@ func (c *Config) Validate() error {
 		return fmt.Errorf("rateLimit must be at least %d", MinRateLimit)
 	}
 
+	// Validate refresh grace period
+	if c.RefreshGracePeriodSeconds < 0 {
+		return fmt.Errorf("refreshGracePeriodSeconds cannot be negative")
+	}
+
 	return nil
 }
 
-// isValidSecureURL checks if the provided string is a valid HTTPS URL
+// isValidSecureURL checks if a given string represents a valid, absolute HTTPS URL.
+// It uses url.Parse and checks for a nil error, an "https" scheme, and a non-empty host.
+//
+// Parameters:
+//   - s: The URL string to validate.
+//
+// Returns:
+//   - true if the string is a valid HTTPS URL, false otherwise.
 func isValidSecureURL(s string) bool {
 	u, err := url.Parse(s)
 	return err == nil && u.Scheme == "https" && u.Host != ""
 }
 
-// isValidLogLevel checks if the provided log level is valid
+// isValidLogLevel checks if the provided log level string is one of the supported values ("debug", "info", "error").
+//
+// Parameters:
+//   - level: The log level string to validate.
+//
+// Returns:
+//   - true if the log level is valid, false otherwise.
 func isValidLogLevel(level string) bool {
 	return level == "debug" || level == "info" || level == "error"
 }
@@ -216,14 +260,20 @@ type Logger struct {
 	logDebug *log.Logger
 }
 
-// NewLogger creates a new Logger with the specified log level.
-// The log level determines which messages are output:
-//   - "debug": Outputs all messages (debug, info, error)
-//   - "info": Outputs info and error messages
-//   - "error": Outputs only error messages
+// NewLogger creates and configures a new Logger instance based on the provided log level.
+// It initializes loggers for ERROR (stderr), INFO (stdout), and DEBUG (stdout) levels,
+// enabling output based on the specified level:
+//   - "error": Only ERROR messages are output.
+//   - "info": INFO and ERROR messages are output.
+//   - "debug": DEBUG, INFO, and ERROR messages are output.
 //
-// Error messages are always written to stderr, while info and debug
-// messages are written to stdout when enabled.
+// If an invalid level is provided, it defaults to behavior similar to "error".
+//
+// Parameters:
+//   - logLevel: The desired logging level ("debug", "info", or "error").
+//
+// Returns:
+//   - A pointer to the configured Logger instance.
 func NewLogger(logLevel string) *Logger {
 	logError := log.New(io.Discard, "ERROR: TraefikOidcPlugin: ", log.Ldate|log.Ltime)
 	logInfo := log.New(io.Discard, "INFO: TraefikOidcPlugin: ", log.Ldate|log.Ltime)
@@ -245,51 +295,77 @@ func NewLogger(logLevel string) *Logger {
 	}
 }
 
-// Info logs an informational message.
-// These messages are intended for general operational information
-// and are written to stdout.
+// Info logs a message at the INFO level using Printf style formatting.
+// Output is directed to stdout if the configured log level is "info" or "debug".
+//
+// Parameters:
+//   - format: The format string (as in fmt.Printf).
+//   - args: The arguments for the format string.
 func (l *Logger) Info(format string, args ...interface{}) {
 	l.logInfo.Printf(format, args...)
 }
 
-// Debug logs a debug message.
-// These messages are only output when debug level logging is enabled
-// and are intended for detailed troubleshooting information.
+// Debug logs a message at the DEBUG level using Printf style formatting.
+// Output is directed to stdout only if the configured log level is "debug".
+//
+// Parameters:
+//   - format: The format string (as in fmt.Printf).
+//   - args: The arguments for the format string.
 func (l *Logger) Debug(format string, args ...interface{}) {
 	l.logDebug.Printf(format, args...)
 }
 
-// Error logs an error message.
-// These messages indicate problems that need attention and are
-// always written to stderr regardless of the log level.
+// Error logs a message at the ERROR level using Printf style formatting.
+// Output is always directed to stderr, regardless of the configured log level.
+//
+// Parameters:
+//   - format: The format string (as in fmt.Printf).
+//   - args: The arguments for the format string.
 func (l *Logger) Error(format string, args ...interface{}) {
 	l.logError.Printf(format, args...)
 }
 
-// Infof logs an informational message using Printf formatting.
-// These messages are intended for general operational information
-// and are written to stdout.
+// Infof logs a message at the INFO level using Printf style formatting.
+// Equivalent to calling l.Info(format, args...).
+// Output is directed to stdout if the configured log level is "info" or "debug".
+//
+// Parameters:
+//   - format: The format string (as in fmt.Printf).
+//   - args: The arguments for the format string.
 func (l *Logger) Infof(format string, args ...interface{}) {
 	l.logInfo.Printf(format, args...)
 }
 
-// Debugf logs a debug message using Printf formatting.
-// These messages are only output when debug level logging is enabled
-// and are intended for detailed troubleshooting information.
+// Debugf logs a message at the DEBUG level using Printf style formatting.
+// Equivalent to calling l.Debug(format, args...).
+// Output is directed to stdout only if the configured log level is "debug".
+//
+// Parameters:
+//   - format: The format string (as in fmt.Printf).
+//   - args: The arguments for the format string.
 func (l *Logger) Debugf(format string, args ...interface{}) {
 	l.logDebug.Printf(format, args...)
 }
 
-// Errorf logs an error message using Printf formatting.
-// These messages indicate problems that need attention and are
-// always written to stderr regardless of the log level.
+// Errorf logs a message at the ERROR level using Printf style formatting.
+// Equivalent to calling l.Error(format, args...).
+// Output is always directed to stderr, regardless of the configured log level.
+//
+// Parameters:
+//   - format: The format string (as in fmt.Printf).
+//   - args: The arguments for the format string.
 func (l *Logger) Errorf(format string, args ...interface{}) {
 	l.logError.Printf(format, args...)
 }
 
-// handleError writes an error message to both the HTTP response and the error log.
-// It ensures consistent error handling across the middleware by logging the error
-// and sending an appropriate HTTP response to the client.
+// handleError logs an error message using the provided logger and sends an HTTP error
+// response to the client with the specified message and status code.
+//
+// Parameters:
+//   - w: The http.ResponseWriter to send the error response to.
+//   - message: The error message string.
+//   - code: The HTTP status code for the response.
+//   - logger: The Logger instance to use for logging the error.
 func handleError(w http.ResponseWriter, message string, code int, logger *Logger) {
 	logger.Error(message)
 	http.Error(w, message, code)