Complete Tutorial in: https://ionicthemes.com/tutorials/about/ionic2-google-login
In this post you will learn how to add Google Native Login to your Ionic 2 app. I will explain you why I think this approach is the best you can take.
As an example we are going to build a simple app that allows users to login to your app using their GooglePlus account. Once they log in, they will see a home page with their basic profile info.
Note: This post is for Ionic 2. If you are working with Ionic 1 go here.