Run a script when a user hits a home assistant static page


I want to create a little advent surprise so that when a user hits a static page home assistant will start playing a video on the TV.

So I’ve got a script to play a video via Chromecast and that works.

Now I want to be able to execute the script when the user goes to a webpage. So I have created a static page in ${ha_config}/www/advent.html now how can I execute the script when the user requests the page? I tried using a Ajax post request but I get an authenticaion error:

    url: 'REDACTED_URL/api/services/script/turn_on',
    type: 'post',
    data: {
        "entity_id": "script.advent_script",
    headers: {
      'Authorization': 'Bearer REDACTED_TOKEN'
    dataType: 'application/json',
    success: function (data) {;

Any ideas what I need to do? I can also run this on another web server if required but I figure with cross site scripting issues this will be easier.