Introducing Google+ Sign-In: simple and secure, minus the social spam

Today we’re adding a new feature to the Google+ platform: application
sign-in. Whether you’re building an app for Android, iOS or the web, users
can now sign in to your app with Google, and bring along their Google+ info
for an upgraded experience. It’s simple, it’s secure, and it prohibits
social spam. And we’re just getting started.

http://googleplusplatform.blogspot.cz/2013/02/google-plus-sign-in.html