code: func (h *DeployHandler) authenticatedClient() (project string, hc *http.Client, err error) {
  	var ctx = context.Background()
  
  	project = os.Getenv("CAMLI_GCE_PROJECT")
  	accountFile := os.Getenv("CAMLI_GCE_SERVICE_ACCOUNT")
  	if project != "" && accountFile != "" {
  		data, errr := ioutil.ReadFile(accountFile)
  		err = errr
  		if err != nil {
  			return
  		}
  		jwtConf, errr := google.JWTConfigFromJSON(data, "https://www.googleapis.com/auth/compute.readonly")
  		err = errr
  		if err != nil {
  			return
  		}
  		hc = jwtConf.Client(ctx)
  		return
  	}
  	if !metadata.OnGCE() {
  		err = errNoRefresh
  		return
  	}
  	project, _ = metadata.ProjectID()
  	hc, err = google.DefaultClient(ctx)
  	return project, hc, err
  }
docs: // authenticatedClient returns the GCE project running the /launch/
  // app (e.g. "camlistore-website" usually for the main instance) and
  // an authenticated OAuth2 client acting as that service account.
  // This is only used for refreshing the list of valid zones to give to
  // the user in a drop-down.
  // If we're not running on GCE (e.g. dev mode on localhost) and have
  // no other way to get the info, the error value is is errNoRefresh.