title: no signed_request on FIRST view via page tab
body: <p>I'm having a problem with my page tab.
  When I access the app via the page tab the first time (e.g. logout, change browser, delete all cookies), I don't get the signed_request.
  Here's (a part of) my code (I'm using the newest PHP SDK):</p>
  
  <pre><code>require_once ('facebook.php');
  $app_id = "xxx";
  $app_secret = "xxx";
  $facebook = new Facebook(array(
                            'appId' =&gt; $app_id,
                            'secret' =&gt; $app_secret,
                            'cookie' =&gt; true
                       ));
  
  
  
  $signed_request = $facebook-&gt;getSignedRequest();
  $page_id = $signed_request['page']['id'];
  </code></pre>
  
  <p>$page_id is empty the first time I open the page tab. When I click the page tab again, everthing's fine and $page_id gets populated.</p>
  
  <p>What am I doing wrong?
  I found possible solutions on stackoverflow, but they don't work for me:
  "signed_request for Canvas" is enabled and my page tab url ends with "tab.php".</p>
  
  <p>Thanks a lot!</p>