title: Creating unique users for a leaderboard in iOS game
body: <p>I'm looking at implementing a leaderboard in to my iOS game, and after a little research I've decided to use Firebase to store the leaderboard data.</p>
  
  <p>Users in the game can login via Facebook and their userID is then used to create a unique record in Firebase.  However, for players who don't want to authenticate via Facebook or the other methods (Email, phone number, etc) how would I go about creating a unique ID in the game so they can still post their scores to Firebase?</p>