OpenID for Google Apps - Account Authentication API - Google Code. If you need information about creating an OpenID 2.0–based web application that accepts Google login authentication, see OpenID 2.0 (Deprecated).
For information about using OpenID 2.0 authentication with Google Apps (hosted) accounts, see OpenID API for Google Apps accounts. This document provides details about updating your code away from OpenID 2.0. The first section describes why you might want to switch to Google+ Sign-In and gives a few tips on switching. If you cannot switch to Google+ Sign-In or do not want to, the rest of this document provides step-by-step instructions for updating an OpenID 2.0 authentication process to use OAuth 2.0 (OpenID Connect). Yubico. JanRain OpenID Library.