I am trying to send a post request using Javascript, but the problem is that I do not seem to be able to add custom headers to the request.

The request that I want to send:

OPTIONS /startScan?domain=asite.com&user=38 HTTP/2
Host: MYHOST
Accept: */*
Access-Control-Request-Method: POST
Authorization: A_TOKEN
Origin: http://localhost
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.54 Safari/537.36
Sec-Fetch-Mode: cors
Sec-Fetch-Site: cross-site
Sec-Fetch-Dest: empty
Referer: http://localhost/
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9

note that MYHOST and A_TOKEN are in my case other values, but replaced them for security reasons.

The request that I send:

OPTIONS /startScan?domain=asite.comm&user=38 HTTP/2
Host: MYHOST
Accept: */*
Access-Control-Request-Method: POST
Access-Control-Request-Headers: authorization,content-type
Origin: http://localhost
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.54 Safari/537.36
Sec-Fetch-Mode: cors
Sec-Fetch-Site: cross-site
Sec-Fetch-Dest: empty
Referer: http://localhost/
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9

The code that I use to send this:

var data = JSON.stringify({
    "domain": "asite.com",
    "user": 38
    });

    var xhr = new XMLHttpRequest();
    xhr.withCredentials = true;

    xhr.addEventListener("readystatechange", function() {
    if(this.readyState === 4) {
        console.log(this.responseText);
    }
    });

    xhr.open("POST", "MYHOST/startScan?domain=asite.com&user=38");
    xhr.setRequestHeader("Content-Type", "application/json");
    xhr.setRequestHeader("Authorization", "A_TOKEN");

    xhr.send(data);

The problem:

The problem now is that I am not able to add a custom header to this request. Instead of adding a header that is called Authorization I add a Access-Request-Control-Header which has authorization as value. I have tried using jQuery, XHR (as you can see) and Fetch, but no success with all of them. Can anyone help me?