title: Facebook iOS SDK to return a signed request object upon login
body: <p>The JavaScript SDK returns a signed request object which can be used to authenticate the user in the backend (the applications backend, that is). This is particularly useful, because the signed request object is signed with a shared secret. That allows to verify, that the Facebook id that is contained in the signed object is the actual user and not an impostor.</p>
  
  <p>The same would be great for the iOS SDK as well. From where I'm standing, it looks like it is using the same dialog/oauth call where one can pass in</p>
  
  <pre><code>response_type=token,signed_request,code&amp;sdk=joey.
  </code></pre>
  
  <p>I found the code in Facebook.m Facebook::authorizeWithFBAppAuth[164] where the params for the call are being setup. So I tried to add signed_request as a response type. However I could not get it to work. Any pointers?</p>
  
  <p>Here is the code I've tried:</p>
  
  <pre><code>NSMutableDictionary* params = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                               _appId, @"client_id",
                               @"user_agent", @"type",
                               kRedirectURL, @"redirect_uri",
                               @"touch", @"display",
                               @"token,signed_request,code", @"response_type",
                               kSDK, @"sdk",
                               nil];
  </code></pre>