Retrieve User ID of Facebook App Invitor - facebook

Question

In the context of a given Facebook app, suppose User A invited user B to start using it. Once User B accepts to use the app, is there any way to retrieve the ID of User A programmatically (via either PHP/JS SDK) ? This doesn't seem quite documented.
For what it's worth, A/B users are friends, if it's any use.

Answer 1

when user comes following the app request, you can get request id's using
$_GET['request_ids']
then retrieve all the request ids with which you can call graph api to get the corresponding request details like below:
if(isset($_GET['request_ids']))
{
$request_ids = $_GET['request_ids'];
}
$request_ids = explode(",", $request_ids);
foreach($request_ids as $request_id)
{
$request_object = $facebook->api($request_id);
//this $request_object have sender facebook id in the field uid_from
}

Answer 2

If you look here:
http://developers.facebook.com/docs/reference/dialogs/requests/
You can see the object layout. Of note is the data property:
Optional, additional data you may pass for tracking. This will be
stored as part of the request objects created. The maximum length is
255 characters.
In this object you can add your referring UserId and then when the request is claimed, you can then process it on your end.
Hope this helps.