CakePHP Auth how to allow specific controller and actions

The period will not work. You could try '/' instead. If that fails as well, you should set $this->Auth->allow('index') in PostController's and UserController's ::beforeFilter() individually. Don't forget to call parent::beforeFilter().

Depends on the version you're working on. If it's cakephp 2.x, put this code into the controller that has the action you want give access without login. As your question, you should put this code to Posts controller:

function beforeFilter(){
     $this->Auth->allow(array('index','another action'));}

allow(array('acction you want to allow')) instead allow('acction you want to allow')