gistfile1.txt

- (void) authenticateLocalPlayer
{
    GKLocalPlayer *localPlayer = [GKLocalPlayer localPlayer];
    localPlayer.authenticateHandler = ^(UIViewController *viewController, NSError *error){
        self.authenticated = NO;
        if (viewController != nil)
        {
            [self presentViewController:viewController];
        } else if (localPlayer.isAuthenticated) {
            if (![self.playerId isEqualToString:localPlayer.playerID]) {
                self.playerId = localPlayer.playerID;
                DLog(@"[GameCenter] New Player: %@", self.playerId);
            } else {
                DLog(@"[GameCenter] Reauthenticated: %@", self.playerId);
            }
            self.authenticated = YES;
        } else {
            DLog(@"Player not authenticated: %@", [error description]);
            self.playerId = nil;
        }
    };
}