title: Get Facebook real user ID
body: <p>I have App on Facebook, and this code using FB JS-SDK:</p>
  
  <pre><code>FB.login(function(response) {
      if (response.authResponse) {
          FB.api('/me', {fields: 'first_name, last_name, email'}, function(response) {
              var user_id = response.id;
              ...
          });
      }
  }, {scope: 'public_profile,email'});
  </code></pre>
  
  <p>The <code>user_id</code> returns only user ID that belongs to my APP. But how can I retrieve the real Facebook user ID from this ID?</p>
  
  <p>I need to show profile using this URL: <a href="https://www.facebook.com/profile.php?id=XXXX" rel="nofollow">https://www.facebook.com/profile.php?id=XXXX</a>.</p>