奇怪的getSessionFromRedirect（）在CodeIgniter中返回null

I am using Facebook SDK in Facebook. All I am trying to do is login and get user details.

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
if ( session_status() == PHP_SESSION_NONE ) {
 session_start();
}
// Autoload the required files
require_once( APPPATH . 'libraries/facebook/vendor/autoload.php' );
use Facebook\FacebookRedirectLoginHelper;
use Facebook\FacebookSession;
use Facebook\FacebookRequest;
class Facebook {
 var $ci;
 var $helper;
 var $session;
 var $permissions;
 public function __construct() {
 $this->ci =& get_instance();
 $this->permissions = $this->ci->config->item('permissions', 'facebook');
 // Initialize the SDK
 FacebookSession::setDefaultApplication( $this->ci->config->item('api_id', 'facebook'), $this->ci->config->item('app_secret', 'facebook') );

$this->helper = new FacebookRedirectLoginHelper( $this->ci->config->item('redirect_url', 'facebook') );
if ( $this->ci->session->userdata('fb_token') ) {
  $this->session = new FacebookSession( $this->ci->session->userdata('fb_token') );
  // Validate the access_token to make sure it's still valid
  try {
    if ( ! $this->session->validate() ) {
      $this->session = null;
    }
  } catch ( Exception $e ) {
    // Catch any exceptions
    $this->session = null;
  }
} else {
  // No session exists
  try {
    $this->session = $this->helper->getSessionFromRedirect();
  } catch( FacebookRequestException $ex ) {
    // When Facebook returns an error
  } catch( Exception $ex ) {
    // When validation fails or other local issues
  }
}
if ( $this->session ) {
  $this->ci->session->set_userdata( 'fb_token', $this->session->getToken() );
  $this->session = new FacebookSession( $this->session->getToken() );
}
  }
  /**
   * Returns the login URL.
   */
  public function login_url() {
    return $this->helper->getLoginUrl( $this->permissions );
  }
  /**
       * Returns the current user's info as an array.
   */
      public function get_user() {
       if ( $this->session ) {
     /**
          * Retrieve User’s Profile Information
     */
     // Graph API to request user data
      $request = ( new FacebookRequest( $this->session, 'GET', '/me' ) )->execute();
  // Get response as an array
  $user = $request->getGraphObject()->asArray();
  return $user;
}
return false;
  }
}

I am trying to work with Localhost.

The strange things is that when I view source of the generated view, it works when the login URL generated from $this->helper->getLoginUrl( $this->permissions ); is clicked.

Otherwise, getSessionFromRedirect() returns null.

I have tried everything from last two days, searched for every possible solution in stackoverflow and I am still without any progress.