Users to log in to an Android application with Google account

I want to enable the users to log in to my application via their Google account. I was reading topics on the web, for example this one where you log i开发者_JAVA技巧n with a google account using OAuth and you can access contact, calendars etc. for further use. I don't need this - I just want to acquire the user id after a successful user/password input. How would you suggest to do this?