code: func newVerifyHandler(token string) func(w http.ResponseWriter, r *http.Request) {
  	return func(w http.ResponseWriter, r *http.Request) {
  		if r.FormValue("hub.verify_token") == token {
  			fmt.Fprintln(w, r.FormValue("hub.challenge"))
  			return
  		}
  		fmt.Fprintln(w, "Incorrect verify token.")
  	}
  }
docs: // newVerifyHandler returns a function which can be used to handle webhook verification