example for loggin in guests in CakePHP 2.x

AppController.php

<?php
App::uses('Controller', 'Controller');

class AppController extends Controller {

	public $components = array(
		'Auth' => array(
			'authorize' => 'Controller',
		),
		'Session'
	);

	public function beforeFilter() {
		if ($this->action !=  'login' && !$this->Auth->user()) {
			$this->Auth->login('guest');
		}
	}

	public function isAuthorized() {
		$role = $this->Auth->user('role');
		if ($role == 'admin') {
			return true;
		} elseif ($role == 'user') {
			if (in_array($this->action, array('edit', 'delete'))) {
				return false;
			}
			return true;
		}
		if (in_array($this->action, array('index', 'view'))) {
			return true;
		}
		return false;
	}
}