getSignedRequest Facebook SDK 4

Question

I'm creating a Fan gate on Facebook SDK 4,

I'm trying to use $signed_request = $facebook->getSignedRequest();

However, I'm currently not sure which object I should be calling getSignedRequest() on.

The doc says $facebook, when I create a $facebook object from
$facebook = FacebookSession::setDefaultApplication('app_id 'secret');

I get the following error

Fatal error: Call to a member function getSignedRequest() on a non-object 

CODE

$facebook = FacebookSession::setDefaultApplication('app_id', 'secret);

// login helper with redirect_uri
$helper = new FacebookRedirectLoginHelper( 'http://www.metah.ch/' );

try {
  $session = $helper->getSessionFromRedirect();
} catch( FacebookRequestException $ex ) {
  // When Facebook returns an error
} catch( Exception $ex ) {
  // When validation fails or other local issues
}

$signed_request = $facebook->getSignedRequest();

var_dump($signed_request);

Answer 1

I don't imagine that FacebookSession::setDefaultApplication('app_id', 'secret'); returns a facebook object. You can try to var_dump($facebook); to confirm.

The docs didn't seem to suggest it returned a facebook object either. https://developers.facebook.com/docs/php/gettingstarted/4.0.0

I haven't used the SDK in some time but it used to be that you'd do new Facebook() to get a facebook object. The docs seem to indicate the getSignedRequest method exists in the BaseFacebook class. https://developers.facebook.com/docs/reference/php/facebook-getSignedRequest