code: func (s *ProviderServer) Present(domain, token, keyAuth string) error {
  	if s.port == "" {
  		s.port = "80"
  	}
  
  	var err error
  	s.listener, err = net.Listen("tcp", s.GetAddress())
  	if err != nil {
  		return fmt.Errorf("could not start HTTP server for challenge -> %v", err)
  	}
  
  	s.done = make(chan bool)
  	go s.serve(domain, token, keyAuth)
  	return nil
  }
docs: // Present starts a web server and makes the token available at `ChallengePath(token)` for web requests.