Detecting if user doesn't want to sign in with Play Game Services

So basically I have a script which prompts the user to sign in with google play games and the script is run everytime the user opens my game. If he signs, then he won't see it again, but if he doesn't everytime he opens the game the log in screen will open. I need a way to detect if the player presses cancel, and if he presses cancel to not run the authentication process.