code: public static Map<String, Object> nok(Map<String, Object> msg, String error) {
  		HashMap<String, Object> r = new HashMap<>();
  		r.put((String) msg.get("cmd"), "NOK");
  		r.put("session", msg.get("session"));
  		if (error != null) {
  			r.put("ERROR", error);
  		}
  		return r;
  	}
docs: User by client