code: func (state *UserState) UsernameCookie(req *http.Request) (string, error) {
  	username, ok := cookie.SecureCookie(req, "user", state.cookieSecret)
  	if ok && (username != "") {
  		return username, nil
  	}
  	return "", ErrCookieGetUsername
  
  }
docs: // Retrieve the username that is stored in a cookie in the browser, if available.