code: func FetchLUCIServiceIdentity(c context.Context, serviceURL string) (identity.Identity, error) {
  	info, err := FetchServiceInfoFromLUCIService(c, serviceURL)
  	if err != nil {
  		return "", err
  	}
  	return identity.MakeIdentity("service:" + info.AppID)
  }
docs: // FetchLUCIServiceIdentity returns "service:<app-id>" of a LUCI service.
  //
  // It is the same thing as inf.AppID returned by FetchServiceInfoFromLUCIService
  // except it is cached more aggressively because service ID is static (unlike
  // some other ServiceInfo fields).
  //
  // 'serviceURL' is root URL of the service (e.g. 'https://example.com').