title: Get Facebook user ID in FB PHP SDK 4.0
body: <p>In FB SDK 3.0, you could run <code>$facebook-&gt;getUser()</code> to get the user's Facebook UID.</p>
  
  <p>SDK 4.0 doesn't have a BaseFacebook object any more; I can't see how to get the user ID off of a FacebookSession created by FacebookJavaScriptLoginHelper. How do you do it?</p>