code: func GetConfigServiceAppID(c context.Context) (string, error) {
  	s, err := FetchCachedSettings(c)
  	switch {
  	case err != nil:
  		return "", err
  	case s.ConfigServiceHost == "":
  		return "", nil
  	}
  	info, err := signing.FetchServiceInfoFromLUCIService(c, "https://"+s.ConfigServiceHost)
  	if err != nil {
  		return "", err
  	}
  	return info.AppID, nil
  }
docs: // GetConfigServiceAppID looks up the app ID of the LUCI Config service, as set
  // in the app's settings.
  //
  // Returns an empty string if the LUCI Config integration is not configured for
  // the app.