Client-Side or Server-Side?
While in this case we’ll be running Google+ Sign-In authentication on the client side, you have the option to run it server-side. You might use a server-side flow if you want to execute call Google APIs while the user isn’t actively logged in. The scope of this article will be the client-side login flow. Even if your goal is a server-side flow, I encourage you to keep reading as the server-side flow merely adds a few steps to those that will be outlined here.