Symfony2 + Facebook API：无法检索会话对象

I try to integrate FB functionality in my Symfony2 app.

I have a base.html.twig where I initialise the javascript facebook api:

<script>
  window.fbAsyncInit = function() {
    FB.init({
      appId      : '{{ fb_appid }}',
      xfbml      : false,
      version    : 'v2.1'
    });

    FB.getLoginStatus(function(response) {
      statusChangeCallback(response);
    });
  };

  (function(d, s, id){
     var js, fjs = d.getElementsByTagName(s)[0];
     if (d.getElementById(id)) {return;}
     js = d.createElement(s); js.id = id;
     js.src = "//connect.facebook.net/de_DE/sdk.js";
     fjs.parentNode.insertBefore(js, fjs);
   }(document, 'script', 'facebook-jssdk'));
</script>

Then, in my DefaultController.php I want to retrieve the session and after that the current logged in users facebook id:

use Facebook\FacebookSession;
use Facebook\FacebookRequest; 
use Facebook\FacebookJavaScriptLoginHelper;

/**
 * @Route("/overview", name="_overview")
 * @Template()
 */
public function overviewAction()
{
    $helper = new FacebookJavaScriptLoginHelper();
    try {
      $session = $helper->getSession();
    } catch(FacebookRequestException $ex) {
      // When Facebook returns an error
        echo $ex."<br>";
    } catch(\Exception $ex) {
      // When validation fails or other local issues
        echo $ex."<br>";
    }
    if ($session) {
      // Logged in
        echo "some";
    }else{
        echo "none";
    }
}

And all I get is "none".

I dont know why I have no session, because the javascript method gives me the "connected" status.. so user is logged into facebook and have permitted my app.

Could anyone help me a little on this please, since this should not be such a difficult task?! Thanks in advance :)

Ok I've found out by myself: I had to configure cookie and status on Fb.init()

  window.fbAsyncInit = function() {
    FB.init({
      appId      : '{{ fb_appid }}',
      xfbml      : false,
      version    : 'v2.1',
      cookie     : true,
      status     : true
    });