Create a website to login in with Gmail, Yahoo, or Facebook accounts

Question

How does Stack Overflow allow new users to login into Stack Overflow using their Gmail or Facebook or Yahoo accounts? I am working on a little project website and I was curi

Answer 1

StackOverflow (and all other StackExchange sites) use OpenID.

OpenID is a decentralized authentication protocol that makes it easy for people to sign up and access web accounts.

Yahoo, Google and facebook are all OpenID providers, so simply implementing it on your site will be enough for your users to be able to login using them (and any other OpenID provider).

There is no need to get permission - the permission will be gotten by the users of your application.