title: iOS Game Player IDs
body: <p>I am going to work on a game project for the first time. I have some thoughts in pieces, but couldn't get all things to make sense.</p>
  
  <p><strong>The Game can only be played if the user is logged in.</strong>
  Plan to let user has the following options to login:</p>
  
  <ol>
  <li>Game Center ID</li>
  <li>Facebook ID</li>
  <li>registered ID (email/username/password) with my server.</li>
  </ol>
  
  <p>Question: does it make sense? Looks like there is no API to get user's Game Center ID, so that I can post it to my server.
  For Facebook ID, I can get it and post to server. 
  Registered ID surely no programed.</p>
  
  <p>I need those IDs to be posted to server because, I need to keep record in server for a game achievement award system by us, apart from Game Center's Leader Board.</p>
  
  <p>Thanks in advance.</p>