How to Save quiz attempt Step data in Moodle?

I am writing a custom Moodle (2.6) web service for taking up the moodle quiz, that requires to create an attempt or start an attempt. I written the API to start an attempt as well as get the questions for a particular quiz. However I m not able to figure out how to save the User responses for the question attempt. (Question attempt step data). Will appreciate if anyone can help me.

    //Fetch all the user attempts

    $attempts = quiz_get_user_attempts($quizObj->get_quizid(), 3, 'all', true);

    //Get the last attempt

    $lastattempt = end($attempts);


    // Delete any previous preview attempts belonging to this user.
    quiz_delete_previews($quizObj->get_quiz(), $USER->id);

    //fetch the quiz usage object
    $quba = question_engine::make_questions_usage_by_activity('mod_quiz', $quizObj->get_context());


    $quba->set_preferred_behaviour($quizObj->get_quiz()->preferredbehaviour);


    // Create the new attempt and initialize the question sessions
    $timenow = time(); // Update time now, in case the server is running really slowly.
    $attempt = quiz_create_attempt($quizObj, $attemptnumber, $lastattempt, $timenow, $quizObj->is_preview_user());


    if ($lastAttemptStatus == quiz_attempt::FINISHED) {
        $attemptnumber = $lastattempt->attempt + 1;

        $attempt = quiz_start_new_attempt($quizObj, $quba, $attempt, $attemptnumber, $timenow);


    } elseif ($lastAttemptStatus == quiz_attempt::IN_PROGRESS) {
        $attempt = quiz_start_attempt_built_on_last($quba, $attempt, $lastattempt);

    }

// It is here Lets say I would like to hardcode (get param) the responses from the user for a quiz for a specific question must go.. and I have add these responses as attempt step data..

    $transaction = $DB->start_delegated_transaction();


    $attempt = quiz_attempt_save_started($quizObj, $quba, $attempt);
    quiz_fire_attempt_started_event($attempt, $quizObj);

    $transaction->allow_commit();

    $lastattempt = end($attempts);