Multiple improvements.

* Add todo list.

* fixup! Add todo list.

* fixup! fixup! Add todo list.

* fixup! fixup! fixup! Add todo list.

* Improve the session handling and cache.

* Fix an issue where expired session can cause infinite redirect loop

* fixup! Fix an issue where expired session can cause infinite redirect loop

* Add semver setup for automatic releases.

* fixup! Add semver setup for automatic releases.

* fixup! fixup! Add semver setup for automatic releases.

* fixup! fixup! fixup! Add semver setup for automatic releases.

cache.go

@@ -1,172 +1,153 @@
 package traefikoidc
 
 import (
+	"container/list"
 	"sync"
 	"time"
 )
 
 // CacheItem represents an item stored in the cache with its associated metadata.
 type CacheItem struct {
-	// Value is the cached data of any type
+	// Value is the cached data of any type.
 	Value interface{}
 
-	// ExpiresAt is the timestamp when this item should be considered expired
-	// and removed from the cache during cleanup operations
+	// ExpiresAt is the timestamp when this item should be considered expired.
 	ExpiresAt time.Time
 }
 
-// Cache provides a thread-safe in-memory caching mechanism with expiration support.
-// It uses a read-write mutex to ensure safe concurrent access to the cached items.
-type Cache struct {
-	// items stores the cached data with string keys
-	items map[string]CacheItem
-
-	// mutex protects concurrent access to the items map
-	// Use RLock/RUnlock for reads and Lock/Unlock for writes
-	mutex sync.RWMutex
-
-	// maxSize is the maximum number of items allowed in the cache
-	maxSize int
-
-	// accessList maintains the order of item access for eviction
-	accessList []string
+// lruEntry represents an entry in the LRU list.
+type lruEntry struct {
+	key string
 }
 
-// DefaultMaxSize is the default maximum number of items in the cache
+// Cache provides a thread-safe in-memory caching mechanism with expiration support.
+// It implements an LRU (Least Recently Used) eviction policy using a doubly-linked list for efficiency.
+type Cache struct {
+	// items stores the cached data with string keys.
+	items map[string]CacheItem
+
+	// order maintains the usage order; most recently used items are at the back.
+	order *list.List
+
+	// elems maps keys to their corresponding list elements for O(1) access.
+	elems map[string]*list.Element
+
+	// mutex protects concurrent access to the cache.
+	mutex sync.RWMutex
+
+	// maxSize is the maximum number of items allowed in the cache.
+	maxSize int
+}
+
+// DefaultMaxSize is the default maximum number of items in the cache.
 const DefaultMaxSize = 1000
 
-// NewCache creates a new empty cache instance.
-// The cache is immediately ready for use and is thread-safe.
+// NewCache creates a new empty cache instance that is ready for use.
 func NewCache() *Cache {
 	return &Cache{
-		items:      make(map[string]CacheItem),
-		maxSize:    DefaultMaxSize,
-		accessList: make([]string, 0, DefaultMaxSize),
+		items:   make(map[string]CacheItem, DefaultMaxSize),
+		order:   list.New(),
+		elems:   make(map[string]*list.Element, DefaultMaxSize),
+		maxSize: DefaultMaxSize,
 	}
 }
 
 // Set adds or updates an item in the cache with the specified expiration duration.
-// Parameters:
-//   - key: Unique identifier for the cached item
-//   - value: The data to cache (can be of any type)
-//   - expiration: How long the item should remain in the cache
-//
-// Thread-safe: Uses write locking to ensure safe concurrent access.
+// It moves the item to the most recently used position.
 func (c *Cache) Set(key string, value interface{}, expiration time.Duration) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 
-	// If key exists, update it
+	now := time.Now()
+	expTime := now.Add(expiration)
+
+	// Update existing item.
 	if _, exists := c.items[key]; exists {
 		c.items[key] = CacheItem{
 			Value:     value,
-			ExpiresAt: time.Now().Add(expiration),
+			ExpiresAt: expTime,
+		}
+		if elem, ok := c.elems[key]; ok {
+			c.order.MoveToBack(elem)
 		}
 		return
 	}
 
-	// If cache is full, remove oldest item
+	// Evict oldest item if cache is full.
 	if len(c.items) >= c.maxSize {
 		c.evictOldest()
 	}
 
-	// Add new item
+	// Add new item.
 	c.items[key] = CacheItem{
 		Value:     value,
-		ExpiresAt: time.Now().Add(expiration),
+		ExpiresAt: expTime,
 	}
-	c.accessList = append(c.accessList, key)
+	elem := c.order.PushBack(lruEntry{key: key})
+	c.elems[key] = elem
 }
 
 // Get retrieves an item from the cache if it exists and hasn't expired.
-// Parameters:
-//   - key: The identifier of the item to retrieve
-//
-// Returns:
-//   - value: The cached data (nil if not found or expired)
-//   - found: true if the item was found and is valid, false otherwise
-//
-// Thread-safe: Uses read locking to ensure safe concurrent access.
+// Moving the accessed item to the most recently used position.
 func (c *Cache) Get(key string) (interface{}, bool) {
-	c.mutex.RLock()
-	item, found := c.items[key]
-	c.mutex.RUnlock()
-
-	if !found {
-		return nil, false
-	}
-
-	if time.Now().After(item.ExpiresAt) {
-		c.mutex.Lock()
-		c.removeItem(key)
-		c.mutex.Unlock()
-		return nil, false
-	}
-
-	// Update access order
 	c.mutex.Lock()
-	c.updateAccessOrder(key)
-	c.mutex.Unlock()
+	defer c.mutex.Unlock()
+
+	item, exists := c.items[key]
+	if !exists {
+		return nil, false
+	}
+
+	// Check for expiration.
+	if time.Now().After(item.ExpiresAt) {
+		c.removeItem(key)
+		return nil, false
+	}
+
+	// Move item to the back (most recently used).
+	if elem, ok := c.elems[key]; ok {
+		c.order.MoveToBack(elem)
+	}
 
 	return item.Value, true
 }
 
-// Delete removes an item from the cache if it exists.
-// If the item doesn't exist, this operation is a no-op.
-// Thread-safe: Uses write locking to ensure safe concurrent access.
+// Delete removes an item from the cache.
 func (c *Cache) Delete(key string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
-	delete(c.items, key)
+
+	c.removeItem(key)
 }
 
-// Cleanup removes all expired items from the cache.
-// This should be called periodically to prevent memory leaks from
-// expired items that haven't been accessed (and thus not removed during Get operations).
-// Thread-safe: Uses write locking to ensure safe concurrent access.
+// Cleanup removes all expired items from the cache. This should be called periodically
+// to prevent memory bloat from expired entries.
 func (c *Cache) Cleanup() {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 
 	now := time.Now()
-	var newAccessList []string
-
-	for _, key := range c.accessList {
-		if item, exists := c.items[key]; exists && !now.After(item.ExpiresAt) {
-			newAccessList = append(newAccessList, key)
-		} else {
-			delete(c.items, key)
+	for key, item := range c.items {
+		if now.After(item.ExpiresAt) {
+			c.removeItem(key)
 		}
 	}
-
-	c.accessList = newAccessList
 }
 
-// evictOldest removes the least recently used item from the cache
+// evictOldest removes the least recently used item from the cache.
 func (c *Cache) evictOldest() {
-	if len(c.accessList) > 0 {
-		oldest := c.accessList[0]
-		c.removeItem(oldest)
+	elem := c.order.Front()
+	if elem != nil {
+		entry := elem.Value.(lruEntry)
+		c.removeItem(entry.key)
 	}
 }
 
-// removeItem removes an item from both the cache and access list
+// removeItem removes an item from both the cache and the LRU tracking structures.
 func (c *Cache) removeItem(key string) {
 	delete(c.items, key)
-	for i, k := range c.accessList {
-		if k == key {
-			c.accessList = append(c.accessList[:i], c.accessList[i+1:]...)
-			break
-		}
-	}
-}
-
-// updateAccessOrder moves the accessed key to the end of the access list
-func (c *Cache) updateAccessOrder(key string) {
-	for i, k := range c.accessList {
-		if k == key {
-			c.accessList = append(append(c.accessList[:i], c.accessList[i+1:]...), key)
-			break
-		}
+	if elem, ok := c.elems[key]; ok {
+		c.order.Remove(elem)
+		delete(c.elems, key)
 	}
 }