/**
  * return the auth driver
  * @return jIAuthDriver
  * @since 1.2.10
  */
 public static function getDriver()
 {
     if (self::$driver === null) {
         $config = self::loadConfig();
         $db = strtolower($config['driver']);
         $driver = jApp::loadPlugin($db, 'auth', '.auth.php', $config['driver'] . 'AuthDriver', $config[$config['driver']]);
         if (is_null($driver)) {
             throw new jException('jelix~auth.error.driver.notfound', $db);
         }
         self::$driver = $driver;
     }
     return self::$driver;
 }