code: func (m *Manager) ServeHTTPS() error {
  	srv := &http.Server{
  		Addr: ":https",
  		TLSConfig: &tls.Config{
  			GetCertificate: m.GetCertificate,
  		},
  	}
  	return srv.ListenAndServeTLS("", "")
  }
docs: // ServeHTTPS runs an HTTPS web server using TLS certificates obtained by the manager.
  // The HTTPS server obtains TLS certificates as needed and responds to requests
  // by invoking http.DefaultServeMux.
  // ServeHTTPS does not return unitil the HTTPS server fails to start or else stops.
  // Either way, ServeHTTPS can only return a non-nil error, never nil.