code: func (s *CookieStore) Save(r *http.Request, w http.ResponseWriter,
  	session *Session) error {
  	encoded, err := securecookie.EncodeMulti(session.Name(), session.Values,
  		s.Codecs...)
  	if err != nil {
  		return err
  	}
  	http.SetCookie(w, NewCookie(session.Name(), encoded, session.Options))
  	return nil
  }
docs: // Save adds a single session to the response.