title: user id not returning using facebook php sdk
body: <pre><code>$this-&gt;_facebookObj = new Facebook($config); 
  try
  {
     $this-&gt;_userId = $this-&gt;_facebookObj-&gt;getUser();
  }
  catch(Exception $e)
  {
  }
  </code></pre>
  
  <p>I've tried to run this sample code on my local machine with proper application id and secret key.
  But response shows like I need an active access token. So i logged in to the Facebook,
  then i get the user id successfully. 
  but whenever I logged out from Facebook I couldn't run the above sample code. I think its because of session. </p>
  
  <p>How do we run above API when the user's logged in session not available? </p>
  
  <p>I tried the following :</p>
  
  <pre><code>$this-&gt;_facebookObj-&gt;getAccessToken();
  $this-&gt;_facebookObj-&gt;setAccessToken(); 
  </code></pre>
  
  <p>before making the <code>getUser()</code> API.</p>