code: func RunWithManager(r http.Handler, m *autocert.Manager) error {
  	s := &http.Server{
  		Addr:      ":https",
  		TLSConfig: m.TLSConfig(),
  		Handler:   r,
  	}
  
  	go http.ListenAndServe(":http", m.HTTPHandler(nil))
  
  	return s.ListenAndServeTLS("", "")
  }
docs: // RunWithManager support custom autocert manager