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