feat: Add Redis caching layer for policies

This commit introduces a Redis caching layer to the DBAL adapter to improve performance and reduce database load.

Features:
- Policies loaded via `loadPolicy` and `loadFilteredPolicy` are now cached in Redis.
- Configurable Redis connection parameters (host, port, password, database, TTL, prefix).
- Automatic cache invalidation for the main policy cache (`all_policies`) when policies are modified.
- A `preheatCache()` method to proactively load all policies into Redis.
- The adapter remains fully functional if Redis is not configured.

Includes:
- Updates to `Adapter.php` to integrate caching logic.
- Addition of `predis/predis` as a dependency.
- Unit tests for the caching functionality in `AdapterWithRedisTest.php`.
- Documentation in `README.md` for the new feature.

Known limitations:
- Cache invalidation for `loadFilteredPolicy` currently only clears the global `all_policies` key, not specific filtered policy keys, to avoid using `KEYS` in production with Predis.

Author: google-labs-jules[bot]

README.md

@@ -62,6 +62,81 @@ if ($e->enforce($sub, $obj, $act) === true) {
 }
 ```
 
+### Redis Caching
+
+To improve performance and reduce database load, the adapter supports caching policy data using [Redis](https://redis.io/). When enabled, Casbin policies will be fetched from Redis if available, falling back to the database if the cache is empty.
+
+#### Configuration
+
+To enable Redis caching, pass a Redis configuration array as the second argument to the `Adapter::newAdapter()` method or the `Adapter` constructor.
+
+Available Redis configuration options:
+
+*   `host` (string): Hostname or IP address of the Redis server. Default: `'127.0.0.1'`.
+*   `port` (int): Port number of the Redis server. Default: `6379`.
+*   `password` (string, nullable): Password for Redis authentication. Default: `null`.
+*   `database` (int): Redis database index. Default: `0`.
+*   `ttl` (int): Cache Time-To-Live in seconds. Policies stored in Redis will expire after this duration. Default: `3600` (1 hour).
+*   `prefix` (string): Prefix for all Redis keys created by this adapter. Default: `'casbin_policies:'`.
+
+**Example:**
+
+```php
+require_once './vendor/autoload.php';
+
+use Casbin\Enforcer;
+use CasbinAdapter\DBAL\Adapter as DatabaseAdapter;
+
+// Database configuration (as before)
+$dbConfig = [
+    'driver' => 'pdo_mysql',
+    'host' => '127.0.0.1',
+    'dbname' => 'test',
+    'user' => 'root',
+    'password' => '',
+    'port' => '3306',
+];
+
+// Redis configuration
+$redisConfig = [
+    'host' => '127.0.0.1',      // Optional, defaults to '127.0.0.1'
+    'port' => 6379,             // Optional, defaults to 6379
+    'password' => null,         // Optional, defaults to null
+    'database' => 0,            // Optional, defaults to 0
+    'ttl' => 7200,              // Optional, Cache policies for 2 hours
+    'prefix' => 'myapp_casbin:' // Optional, Custom prefix
+];
+
+// Initialize adapter with both DB and Redis configurations
+$adapter = DatabaseAdapter::newAdapter($dbConfig, $redisConfig);
+
+$e = new Enforcer('path/to/model.conf', $adapter);
+
+// ... rest of your Casbin usage
+```
+
+#### Cache Preheating
+
+The adapter provides a `preheatCache()` method to proactively load all policies from the database and store them in the Redis cache. This can be useful during application startup or as part of a scheduled task to ensure the cache is warm, reducing latency on initial policy checks.
+
+**Example:**
+
+```php
+if ($adapter->preheatCache()) {
+    // Cache preheating was successful
+    echo "Casbin policy cache preheated successfully.\n";
+} else {
+    // Cache preheating failed (e.g., Redis not available or DB error)
+    echo "Casbin policy cache preheating failed.\n";
+}
+```
+
+#### Cache Invalidation
+
+The cache is designed to be automatically invalidated when policy-modifying methods are called on the adapter (e.g., `addPolicy()`, `removePolicy()`, `savePolicy()`, etc.). Currently, this primarily clears the cache key for all policies (`{$prefix}all_policies`).
+
+**Important Note:** The automatic invalidation for *filtered policies* (policies loaded via `loadFilteredPolicy()`) is limited. Due to the way `predis/predis` client works and to avoid using performance-detrimental commands like `KEYS *` in production environments, the adapter does not automatically delete cache entries for specific filters by pattern. If you rely heavily on `loadFilteredPolicy` and make frequent policy changes, consider a lower TTL for your Redis cache or implement a more sophisticated cache invalidation strategy for filtered results outside of this adapter if needed. The main `{$prefix}all_policies` cache is cleared on any policy change, which means subsequent calls to `loadPolicy()` will refresh from the database and update this general cache.
+
 ### Getting Help
 
 - [php-casbin](https://github.com/php-casbin/php-casbin)

composer.json

@@ -20,7 +20,8 @@
     "require": {
         "php": ">=8.0",
         "casbin/casbin": "^4.0",
-        "doctrine/dbal": "^3.9|^4.0"
+        "doctrine/dbal": "^3.9|^4.0",
+        "predis/predis": "^2.0"
     },
     "require-dev": {
         "phpunit/phpunit": "~9.0",