code: func updateTransport(stopCh <-chan struct{}, period time.Duration, clientConfig *restclient.Config, clientCertificateManager certificate.Manager, exitAfter time.Duration) (func(), error) {
  	if clientConfig.Transport != nil || clientConfig.Dial != nil {
  		return nil, fmt.Errorf("there is already a transport or dialer configured")
  	}
  
  	d := connrotation.NewDialer((&net.Dialer{Timeout: 30 * time.Second, KeepAlive: 30 * time.Second}).DialContext)
  
  	if clientCertificateManager != nil {
  		if err := addCertRotation(stopCh, period, clientConfig, clientCertificateManager, exitAfter, d); err != nil {
  			return nil, err
  		}
  	} else {
  		clientConfig.Dial = d.DialContext
  	}
  
  	return d.CloseAll, nil
  }
docs: // updateTransport is an internal method that exposes how often this method checks that the
  // client cert has changed.