Codeigniter white list csrf and custom if for fb apps and jquery csrf snippet

MY_Security.php

/* sample code on ajax csrf
$.ajax({
    type: 'POST',
    url: '/action/fetch_more_blog_posts',
    data: {
        type: 'news', limit: limit, offset: offset,
        <?php echo $this->security->get_csrf_token_name(); ?>: '<?php echo $this->security->get_csrf_hash(); ?>' },
    success: function(data) {
        $(data).appendTo('#more-entries');
        $('#older-posts').slideDown();
        offset += limit;
    }
});
*/

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
 
class MY_Security extends CI_Security {
  
	function __construct(){ parent::__construct(); }
	
	public function csrf_verify()
	{
		// If it's not a POST request we will set the CSRF cookie
		if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST')
		{
			
			return $this->csrf_set_cookie();
		}
	
		// this IF statement is the fix
		// Check if URI has been whitelisted from CSRF checks
		if ($exclude_uris = config_item('csrf_exclude_uris'))
		{
			$uri = load_class('URI', 'core');
			$uri_string = $uri->uri_string(); 
			foreach($exclude_uris as $val){								        // i.e.  exempt = array('one', 'abc/def')
				if(is_int(strpos($uri_string,$val))) {		 					// uri == 'one'         returns true
					return $this;												// uri == 'one/two'     returns true
				}																// uri == 'abc'		    returns false
			}																	// uri == 'abc/def'     returns true
		}	
	
		// Do the tokens exist in both the _POST and _COOKIE arrays?
		if ( ! isset($_POST[$this->_csrf_token_name]) OR ! isset($_COOKIE[$this->_csrf_cookie_name])
			OR $_POST[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name]) // Do the tokens match?
		{
      // add if .. check for facebook apps (remove if not from fb apps)
			if(! isset($_POST['signed_request']) || $_POST['signed_request'] == ''){ 
        $this->csrf_show_error();
      }
		}
	
		// We kill this since we're done and we don't want to polute the _POST array
		unset($_POST[$this->_csrf_token_name]);
	
		// Regenerate on every submission?
		if (config_item('csrf_regenerate'))
		{
			// Nothing should last forever
			unset($_COOKIE[$this->_csrf_cookie_name]);
			$this->_csrf_hash = '';
		}
	
		$this->_csrf_set_hash();
		$this->csrf_set_cookie();
	
		log_message('debug', 'CSRF token verified');
		return $this;
	}

}