CakePHP and Facebook with Security Component turned on - facebook

Question

I want the Security Component turned on.
BUT when you load a CakePHP app inside a Facebook tab, FB posts $_REQUEST['signed_request'] to my form - the problem with this is that the Security Component "reacts" to this "post" and gives me validation errors, black-hole, etc.
How do I go around this?
I could not find anything on the documentation to go around this problem.
What I wanted was to somehow run the Security Component "manually" so that it only "reacts" when I actually submit my form and not when Facebook posts the $_REQUEST['signed_request'] to my form.
UPDATE:
<?php
App::uses('CakeEmail', 'Network/Email');
class PagesController extends AppController {
public $helpers = array('Html','Form');
public $components = array('RequestHandler');
public function beforeFilter() {
parent::beforeFilter();
$this->Auth->allow('*');
$this->Security->validatePost = true;
$this->Security->csrfCheck = true;
$this->Security->unlockedFields[] = 'signed_request';
}
public function home() {
$this->loadModel('Memberx');
if($this->request->is('post') && isset($this->request->data['Memberx']['name'])) {
//...save here, etc. ...
}
}
FYI: I get a "black hole" error.
FINAL UPDATE (After #tigrang's answer):
public function beforeFilter() {
parent::beforeFilter();
$this->Auth->allow('*');
$this->set('hasLiked', false);
if(isset($this->request->data['signed_request'])){
$this->set('hasLiked', $this->hasLiked($this->request->data['signed_request']));
}
if(isset($this->request->data['Memberx']['signed_request'])) {
$this->set('hasLiked', $this->hasLiked($this->request->data['Memberx']['signed_request']));
}
/*
To go around Facebook's post $_REQUEST['signed_request'],
we unset the $_REQUEST['signed_request'] and disable the csrfCheck
ONLY after we have set the hasLiked view variable
*/
unset($this->request->data['signed_request']);
if (empty($this->request->data)) {
$this->Security->csrfCheck = false;
}
}
Then, I do something like below in my views:
<?php
if($hasLiked) {
?>
You have liked this page!
<?php
}
?>

Answer 1

public function beforeFilter() {
parent::beforeFilter();
$this->Auth->allow('*');
$this->_validateFbRequest();
}
protected function _valdiateFbRequest() {
if (!isset($this->request->data['signed_request'])) {
// not a valid request from fb
// throw exception or handle however you want
return;
}
$signedRequest = $this->request->data['signed_request'];
unset($this->request->data['signed_request']);
if (empty($this->request->data)) {
$this->Security->csrfCheck = false;
}
// validate the request
}