This feature is a must enabled in your websites/portals to enable your users with highly advanced login facility.
Why Do I Need it?
Adding feature to your users
to login using Social Websites makes your website more user friendly and
reliable. Also it enhances the trust on your website/service. It
reduces your user's time as it just happens in few clicks rather than
typing username and password stuffs.
Create Google API Project.
Configure API Credentials and Auth Credentials
Write Script for Login using Google+ in your website.