title: Why is Facebook PHP SDK getUser always returning 0?
body: <p>I'm trying to work with a website that requires some information from a Facebook user, I'm using PHP and JS SDKs.</p>
  
  <p>I have a function in PHP:</p>
  
  <pre><code>public function isLoggedOnFacebook() {
      $user = $this-&gt;_facebook-&gt;getUser();
      if ($user) {
          return $this-&gt;_facebook-&gt;api("/$user");
      }
      return false;
  }
  </code></pre>
  
  <p>On a class that is holding the facebook object from the SDK in <code>$this-&gt;_facebook</code>.</p>
  
  <p>Then on a block I do this:</p>
  
  <pre><code>&lt;?php if (!$this-&gt;isLoggedOnFacebook()): ?&gt;
  &lt;div&gt;
     &lt;fb:login-button show-faces="true" perms="email" width="500" /&gt;
  &lt;/div&gt;
  &lt;?php endif ?&gt;
  </code></pre>
  
  <p>And the FB JS environment is properly set up (I think) so it works. So the user gets the pop up and authorizes the site.</p>
  
  <p>The problem is even after the app is been authorized by the user $user is always 0, meaning <code>$facebook-&gt;getUser()</code> always returns 0, and then lists the faces of users, including the logged user, but if I make it call <code>$facebook-&gt;api('/me')</code> or whatever, then it'll throw the invalid token exception.</p>
  
  <p>I've seen this problem, but I haven't seen a solution, I have no idea 
  where the problem is and I run out of ideas.</p>
  
  <p>There's a Website tab on the developers' Facebook page in the apps section, where you can set up your Site URL and your Site Domain, and I'm thinking this are the cause of my problem, but I have no knowledge of exactly what these fields are supposed to contain.</p>