ตรวจสอบสิทธิ์โดยใช้ Game Center

let localPlayer = GKLocalPlayer.localPlayer()
localPlayer.authenticateHandler = { (gcAuthViewController?, error) in
  if let gcAuthViewController = gcAuthViewController {
    // Pause any activities that require user interaction, then present the
    // gcAuthViewController to the player.
  } else if localPlayer.isAuthenticated {
    // Player is signed in to Game Center. Get Firebase credentials from the
    // player's Game Center credentials (see below).
  } else {
    // Error
  }
}

__weak GKLocalPlayer *localPlayer = [GKLocalPlayer localPlayer];
localPlayer.authenticateHandler = ^(UIViewController *gcAuthViewController,
                                    NSError *error) {
  if (gcAuthViewController != nil) {
    // Pause any activities that require user interaction, then present the
    // gcAuthViewController to the player.
  } else if (localPlayer.isAuthenticated) {
    // Player is signed in to Game Center. Get Firebase credentials from the
    // player's Game Center credentials (see below).
  } else {
    // Error
  }
};

// Get Firebase credentials from the player's Game Center credentials
GameCenterAuthProvider.getCredential() { (credential, error) in
  if let error = error {
    return
  }
  // The credential can be used to sign in, or re-auth, or link or unlink.
  Auth.auth().signIn(with:credential) { (user, error) in
    if let error = error {
      return
    }
    // Player is signed in!
  }

// Get Firebase credentials from the player's Game Center credentials
[FIRGameCenterAuthProvider getCredentialWithCompletion:^(FIRAuthCredential *credential,
                                                         NSError *error) {
  // The credential can be used to sign in, or re-auth, or link or unlink.
  if (error == nil) {
    [[FIRAuth auth] signInWithCredential:credential
                              completion:^(FIRUser *user, NSError *error) {
      // If error is nil, player is signed in.
    }];
  }
}];

let user = Auth.auth().currentUser
if let user = user {
  let playerName = user.displayName

  // The user's ID, unique to the Firebase project.
  // Do NOT use this value to authenticate with your backend server,
  // if you have one. Use getToken(with:) instead.
  let uid = user.uid
}

FIRUser *user = [FIRAuth auth].currentUser;
if (user) {
  NSString *playerName = user.displayName;

  // The user's ID, unique to the Firebase project.
  // Do NOT use this value to authenticate with your backend server,
  // if you have one. Use getTokenWithCompletion:completion: instead.
  NSString *uid = user.uid;
}

let firebaseAuth = Auth.auth()
do {
  try firebaseAuth.signOut()
} catch let signOutError as NSError {
  print ("Error signing out: %@", signOutError)
}

NSError *signOutError;
BOOL status = [[FIRAuth auth] signOut:&signOutError];
if (!status) {
  NSLog(@"Error signing out: %@", signOutError);
  return;
}