Why must set UserAuthorizationHandler? about oauth2

[wd0517]

oauth2/server/handler.go

Lines 22 to 23 in b369a2d

	// UserAuthorizationHandler get user id from request authorization
	UserAuthorizationHandler func(w http.ResponseWriter, r *http.Request) (userID string, err error)

For authorization code flow, it need to know which user is granting permission to third-party application, since the user is already logged in at this point, you need to implement the UserAuthorizationHandler to retrieve and return the authenticated user.

To run the broken demo in the readme, you can add some dummy code as below:

    ....
    srv.SetClientInfoHandler(server.ClientFormHandler)
    srv.SetUserAuthorizationHandler(func(w http.ResponseWriter, r *http.Request) (userID string, err error) {
        return "1", nil
    })
    .....