code: func (site *installationSite) initClient(ctx context.Context, authFlags authcli.Flags) (err error) {
  	if site.client != nil {
  		return errors.New("client is already initialized")
  	}
  	clientOpts := clientOptions{
  		authFlags:  authFlags,
  		serviceURL: site.cfg.ServiceURL,
  		cacheDir:   site.cfg.CacheDir,
  		rootDir:    site.siteRoot,
  	}
  	site.client, err = clientOpts.makeCIPDClient(ctx)
  	return err
  }
docs: // initClient initializes cipd.Client to use to talk to backend.
  //
  // Can be called only once. Use it directly via site.client.