code: func newAuthenticator(ctx context.Context, credentials, actAs string, scopes []string) *auth.Authenticator {
  	// TODO(vadimsh): Don't hardcode auth options here, pass them from outside
  	// somehow.
  	authOpts := chromeinfra.DefaultAuthOptions()
  	authOpts.ServiceAccountJSONPath = credentials
  	authOpts.Scopes = scopes
  	authOpts.ActAsServiceAccount = actAs
  	return auth.NewAuthenticator(ctx, auth.SilentLogin, authOpts)
  }
docs: // newAuthenticator returns a new authenticator for HTTP requests.