code: func (service *Service) GetOauthUser(r *http.Request, w http.ResponseWriter) (username string, err error) {
  	oauthSession, err := service.GetSession(r, SessionOauth, "oauthsession")
  	if err != nil {
  		log.Error(err)
  		return
  	}
  	err = oauthSession.Save(r, w)
  	if err != nil {
  		log.Error(err)
  		return
  	}
  	savedusername := oauthSession.Values["username"]
  	if savedusername != nil {
  		username, _ = savedusername.(string)
  	}
  	return
  }
docs: // GetOauthUser returns the user in an oauth session, or an empty string if there is none