Creating a login/registration feature into your app is always an important task. But google introduces a one click login button in android and web. Here users do not need to create an account, they can access to their personal area using their existing real email addresses. This tutorial will help you making a login feature using Google Sign In using Firebase in Android Studio.
Full article: http://www.androstock.com/tutorials/google-sign-in-using-firebase-in-android-android-studio.html