trying to use $_SESSION['Auth']['User']['id'] in beforefilter()

I'm trying to use $_SESSION['Auth']['User']['id'] in beforefilter() function in app_controller.php. But I'm getting error message. Error message is -> Undefined variable: _SESSION [APP\app_controller.php Here is my app_controller file. thanks

     `class AppController extends Controller {
         var $components = ar开发者_开发百科ray('Acl', 'Session', 'Auth');
         ....................................`

Use $this->Auth->user('id'), not the $_SESSION variable.
If you insist on reading from the session directly, use $this->Session->read('Auth.User.id').

$_SESSION should be accessible, but that depends on when the session gets started and whether you're using PHP's session management at all. Use Cake's wrappers, they take care of those details.