Allow Authenticated IOS Game Center Users to Auto-Authenticate - iphone

Question

I am making an iphone app (a game) and while it will not be my first game, it will be my first game that uses a network connection (I intend on adding a few multiplier features)
So, now for my question.
I want the player to be able to open my app, sign into game center, and then use that to connect to my server. Is this possible? In other words:
Player signs in to game center
Sends username to my server
if (game center username doesnt exist)
{
Add their username to my sql database
}
else if (username does exist)
{
Send sign in successful message to device.
}
I believe I read another question from a while ago asking how to do this, but the answer said something about using the device UDID, which I do not want to do (for obvious reasons if you read technology related news).
So anyway, is there a trusted way that I can be sure that the user is who they say they are once they authenticate with game center that I can use to authenticate them against my server? Thank you

Answer 1

I think instead of UDID you can use GKPlayer.playerID which is unique to each gamecenter account. For your other purposes you can customize the completion block of authenticate handler
GKLocalPlayer * __weak localPlayer = [GKLocalPlayer localPlayer];
localPlayer.authenticateHandler = ^(UIViewController *viewController, NSError *error)
{
if (viewController != nil)
{
[currentViewController presentViewController:viewController animated:YES completion:nil];
}
else if (localPlayer.isAuthenticated)
{
NSLog(#"Player authenticated");
/* Your custom methods here
Sends username to my server -- send localPlayer.playerID to your server
if (game center username doesnt exist)
{
Add their username to my sql database
}
else if (username does exist)
{
Send sign in successful message to device.
}
*/
}
else
{
NSLog(#"Player not authenticated");
//disableGameCenter
}
NSLog(#"Error: %#",error);
};