Package google provides Google OAuth2 login and callback handlers.
Google login errors
CallbackHandler handles Google redirection URI requests and adds the Google access token and Userinfoplus to the ctx. If authentication succeeds, handling delegates to the success handler, otherwise to the failure handler.
LoginHandler handles Google login requests by reading the state value from the ctx and redirecting requests to the AuthURL with that state value.
StateHandler checks for a state cookie. If found, the state value is read and added to the ctx. Otherwise, a non-guessable value is added to the ctx and to a (short-lived) state cookie issued to the requester.
Implements OAuth 2 RFC 6749 10.12 CSRF Protection. If you wish to issue state params differently, write a http.Handler which sets the ctx state, using oauth2 WithState(ctx, state) since it is required by LoginHandler and CallbackHandler.
UserFromContext returns the Google Userinfoplus from the ctx.
WithUser returns a copy of ctx that stores the Google Userinfoplus.