How to do an ajax post/get to/from a php file?

I’m trying to extend the PiMusicbox by getting the stream uri’s from a local database, to which new streams can be added. I never worked with tornado before, and after reading up on it’s documentation I still can’t figure out how to allow XmlHttpRequests. I have a php file that retrieves data from a database, and I want to post/get data from that file in the controls.js function initStreams.

I was guessing if I had the php file in the same directory as index.html, if i’d do $.ajax({ url: ‘/myfile.php’, method: ‘get’, success: function (response) { console.log(response)} }) (…the usual stuff), I would see the retrieved data in my console, but I got a 405: method not allowed.
After reading up on this, it appears I need to allow XmlHttpRequests in a request handler, but in my situation with the furtheron unchanged pimusicbox webclient, I can’t seem to get this to work…

Anyone has a pretty straightforward answer to this? Or is this not something simple to adjust?
Thanks in advance!