If you would like to have your web site use a social identity provider rather than creating or maintaining your own identity store you’ve got options.
Using an external identity provider means that your users can come to your site and use credentials they already own, and they will be able to grant you the permissions you explicitly request from their identity provider.
You may wish to register your application with one of the following services:
You don’t currently require explicit registration with Google, but you can read more about web sign-in here.