title: Facebook problem: cant get user id into iframe without authorization
body: <p>I have a facebook page with an iframe app.</p>
  
  <p>I want it to be able to work in the same way as <a href="http://www.facebook.com/pepsi" rel="nofollow">http://www.facebook.com/pepsi</a>
  With the following user journey.</p>
  
  <ol>
  <li>User goes app tab on my page.</li>
  <li>User is prompted with a page, partial content, that invites to click the like button    </li>
  <li>User clicks like and is shown full content.</li>
  </ol>
  
  <p>all this is done without the client needing to login or authenticate.</p>
  
  <p>My problem is that facebook is not passing me the user id.</p>
  
  <p>I have tried 
  <code>var_dump($_REQUEST);</code>
  and
  <code>var_dump($fb-&gt;fb_params);</code>
  to see if user id is there but nothing.</p>
  
  <p>I dont think php sdk 3.0 or oauth works for signed_request </p>
  
  <p>Can someone tell me how I get the user id from facebook without login?</p>
  
  <p>thanks</p>