CakePHP：在AppController :: beforeFilter中访问帖子数据

I am using CakePHP 2.3.4.

I found that the post data ($this->request->data) is not ready in AppController::beforeFilter. It is only available when routed to the action methods (e.g. UserController::login).

I found that the post data is available after the Controller::startupProcess where it dispatch a CakeEvent:

$this->getEventManager()->dispatch(new CakeEvent('Controller.startup', $this));

But I cannot make this call in my AppController::beforeFilter as it will let the program free run. Is there is a way to make the post data available in AppController::beforeFilter?