First of all lets see what Oauth 2.0 is, it is an authorization framework that let 3rd party apps to obtain limited and access permission a user account and perform some action on behalf of the user. It uses delegated tokens provided by service that hosts the user account to access user account information. it is important to understand that Oauth 2.0 is not an authentication framework but an authorization framework. Today many sites like Facebook and google provide Oauth 2.0 services.