I tried to do a XHR request inside a HTML rule, but it failed to execute… I used Firefox’s Network tool to monitor the traffic and headers information. I noticed that only a POST request (related to my activity that gets executed) is done when you click the link. The GET request inside the HTML rule gets ignored... The code I used for the XHR request is the following:

<div id="dms-document-viewer"></div>
<script>
var token = "<%= tools.getParamValue("token") %>";
var documentURL = "<%= tools.getParamValue("DocumentURL") %>";

var dmsDocumentViewer = document.getElementById("dms-document-viewer");
var request = new XMLHttpRequest();
request.open('GET', documentURL, true);
request.setRequestHeader("token", token);

request.onload = function() {
  if (request.status >= 200 && request.status < 400) {
    // Success!
    var resp = request.responseText;
    dmsDocumentViewer.innerHTML = resp;
  } else {
    dmsDocumentViewer.innerHTML = "We reached our target server, but it returned an error";
  }
};

request.onerror = function() {
  dmsDocumentViewer.innerHTML = "There was a connection error of some sort";
};

request.send();
</script>

Thanks for any ideas or help in this topic :)