CORS issue while trying to authenticate at Netweaver 7.40

The SAP Gateway doesn't add or doesn't seem to have the option to add CORS headers on reponses to OPTIONS requests. That's why modern browsers block following requests on client side. Therefore, even a request with "x-csrf-token":"fetch" header won't be let through.

The browser sends the OPTIONS preflight, because we need to modify the standard http headers to add an "Authoriztation" header and the "x-csrf-token":"fetch" header mentioned above.

let request = new XMLHttpRequest();
request.open('GET', this.serviceURL);
request.setRequestHeader('Authorization', 'Basic ' + basicAuthToken); // <-Triggers OPTIONS preflight
request.setRequestHeader('x-csrf-token', 'fetch');
request.addEventListener('load', function (event) {
   if (request.status >= 200 && request.status < 300) {
      responseCallback(request);
   } else {
      console.warn(request.statusText, request.responseText);
   }
 });
 request.send();