public String loginWithDropbox(String code, String messageId) {
        Verifier verifier = new Verifier(code);
        Token accessToken = service.getAccessToken(null, verifier);
        String userId = getAccountID(service, accessToken);

        String message = "id | " + messageId + " ; userId | " + userId;
        String response = communicateMulticast(message, messageId);

        if (response.contains("true")) {
            HashMap<String,String> treat = processProtocolMessage(response);
            String username = treat.get("username");
            String password = treat.get("password");
            return login(new Person(username, password), messageId);
        }
        return response;
    }