title: Any way to get facebook user id included in invite callback from notification / app center?
body: <p>When a facebook user clicks on an invitation to my app from either the notification list or the app center, they are redirected to my homepage, and as expected, the link includes the app request id(s).  However, in cases where the user sending the invite selected multiple friends at once, that request id maps to multiple facebook users in my invite records.  In this case, I have no idea who the user is, as the link does not include the facebook user id.  </p>
  
  <p>Of course, if the invitee signs up with their facebook account, I will then be able to retrieve the user id.  However, if they sign up with their email address instead, I won't be able to:</p>
  
  <p>a) delete the facebook request
  b) notify the sender that the invitee joined</p>
  
  <p>So in short, I need the facebook user id included in the invite links - is there any way to make this happen?</p>