code: func (s *StorageOverseer) Del(w http.ResponseWriter, r *http.Request) error {
  	sessID, err := s.options.getCookieValue(w, r)
  	if err != nil {
  		return nil
  	}
  
  	s.options.deleteCookie(w)
  
  	err = s.Storer.Del(sessID)
  	if IsNoSessionError(err) {
  		return nil
  	} else if err != nil {
  		return errors.Wrap(err, "unable to delete server-side session")
  	}
  
  	return nil
  }
docs: // Del deletes the session if it exists and sets the session cookie to expire instantly.