GameCenterPlayerAuth.kt

GKLocalPlayer localPlayer = GKLocalPlayer.localPlayer();
localPlayer.setAuthenticateHandler(new GKLocalPlayer.Block_setAuthenticateHandler() {
    @Override
    public void call_setAuthenticateHandler(UIViewController viewController, NSError nsError) {
        if (viewController != null) {
            iosApplication.getUIWindow().rootViewController().showDetailViewControllerSender(viewController, null);
        } else if (localPlayer.isAuthenticated()) {
            localPlayer.generateIdentityVerificationSignatureWithCompletionHandler(
                new GKLocalPlayer.Block_generateIdentityVerificationSignatureWithCompletionHandler() {
                @Override
                public void call_generateIdentityVerificationSignatureWithCompletionHandler(
                    NSURL publicKeyUrl, NSData signature, NSData salt, long timestamp, NSError error) {
                    //successfully logged into gamecenter
                }
            });
        } else {
            //canceled by the user or GameCenter is disabled
            //display alert view
        }
    }
});