implement session and CSRF handling

context.php

@@ -1,5 +1,7 @@
 <?php
 
+require_once __DIR__ . '/session.php';
+
 /**
  * Context holds the request, response, and shared state for a request
  */
@@ -7,6 +9,7 @@ class Context
 {
     public Request $request;
     public Response $response;
+    public Session $session;
     public array $state = [];
 
     /**
@@ -16,6 +19,8 @@ class Context
     {
         $this->request = new Request();
         $this->response = new Response();
+        $this->session = new Session();
+        $this->session->start();
     }
 
     /**

session.php

@@ -0,0 +1,186 @@
+<?php
+
+/**
+ * Session provides session management with flash messages and CSRF protection
+ */
+class Session
+{
+    private bool $started = false;
+    private array $flashData = [];
+
+    /**
+     * start initializes the session if not already started
+     */
+    public function start(): void
+    {
+        if ($this->started || session_status() === PHP_SESSION_ACTIVE) {
+            $this->started = true;
+            $this->loadFlashData();
+            return;
+        }
+
+        session_start();
+        $this->started = true;
+        $this->loadFlashData();
+    }
+
+    /**
+     * get retrieves a value from the session
+     */
+    public function get(string $key, mixed $default = null): mixed
+    {
+        $this->ensureStarted();
+        return $_SESSION[$key] ?? $default;
+    }
+
+    /**
+     * set stores a value in the session
+     */
+    public function set(string $key, mixed $value): void
+    {
+        $this->ensureStarted();
+        $_SESSION[$key] = $value;
+    }
+
+    /**
+     * has checks if a key exists in the session
+     */
+    public function has(string $key): bool
+    {
+        $this->ensureStarted();
+        return isset($_SESSION[$key]);
+    }
+
+    /**
+     * remove deletes a value from the session
+     */
+    public function remove(string $key): void
+    {
+        $this->ensureStarted();
+        unset($_SESSION[$key]);
+    }
+
+    /**
+     * flash sets a flash message that will be available only for the next request
+     */
+    public function flash(string $key, mixed $value): void
+    {
+        $this->ensureStarted();
+        $_SESSION['_flash_new'][$key] = $value;
+    }
+
+    /**
+     * getFlash retrieves a flash message (available only for current request)
+     */
+    public function getFlash(string $key, mixed $default = null): mixed
+    {
+        return $this->flashData[$key] ?? $default;
+    }
+
+    /**
+     * hasFlash checks if a flash message exists
+     */
+    public function hasFlash(string $key): bool
+    {
+        return isset($this->flashData[$key]);
+    }
+
+    /**
+     * csrfToken generates or retrieves the CSRF token for the session
+     */
+    public function csrfToken(): string
+    {
+        $this->ensureStarted();
+
+        if (!isset($_SESSION['_csrf_token'])) {
+            $_SESSION['_csrf_token'] = bin2hex(random_bytes(32));
+        }
+
+        return $_SESSION['_csrf_token'];
+    }
+
+    /**
+     * validateCsrf validates a CSRF token
+     */
+    public function validateCsrf(string $token): bool
+    {
+        $this->ensureStarted();
+
+        if (!isset($_SESSION['_csrf_token'])) {
+            return false;
+        }
+
+        return hash_equals($_SESSION['_csrf_token'], $token);
+    }
+
+    /**
+     * regenerate regenerates the session ID for security
+     */
+    public function regenerate(bool $deleteOldSession = true): bool
+    {
+        $this->ensureStarted();
+        return session_regenerate_id($deleteOldSession);
+    }
+
+    /**
+     * destroy destroys the session
+     */
+    public function destroy(): void
+    {
+        $this->ensureStarted();
+
+        $_SESSION = [];
+
+        if (ini_get("session.use_cookies")) {
+            $params = session_get_cookie_params();
+            setcookie(session_name(), '', time() - 42000,
+                $params["path"], $params["domain"],
+                $params["secure"], $params["httponly"]
+            );
+        }
+
+        session_destroy();
+        $this->started = false;
+        $this->flashData = [];
+    }
+
+    /**
+     * clear removes all session data but keeps the session active
+     */
+    public function clear(): void
+    {
+        $this->ensureStarted();
+        $_SESSION = [];
+        $this->flashData = [];
+    }
+
+    /**
+     * all returns all session data
+     */
+    public function all(): array
+    {
+        $this->ensureStarted();
+        $data = $_SESSION;
+        unset($data['_flash_old'], $data['_flash_new'], $data['_csrf_token']);
+        return $data;
+    }
+
+    /**
+     * ensureStarted ensures the session is started
+     */
+    private function ensureStarted(): void
+    {
+        if (!$this->started) $this->start();
+    }
+
+    /**
+     * loadFlashData loads flash messages and rotates them
+     */
+    private function loadFlashData(): void
+    {
+        $this->flashData = $_SESSION['_flash_old'] ?? [];
+
+        $_SESSION['_flash_old'] = $_SESSION['_flash_new'] ?? [];
+        unset($_SESSION['_flash_new']);
+    }
+}