JS Post

var request = new XMLHttpRequest();
request.onreadystatechange= function () {
    if (request.readyState==4) {
        request.getAllResponseHeaders().toString();
        //if I receive array('status' => 'Success',) - OK. If not - error. Please help with parsing
    }
};

request.open("POST", " qaapi.staffpass.eu/sppEnable?user_id=295753599", true);
request.setRequestHeader("X-Qaapi-Auth-Secret", "kjdsGju76kjhJHGklk92");
request.setRequestHeader("Accept","text/plain");
request.send("post data"); // what should I add here?