Capture the 401 Authentication code

auth.js

// A lazy raw JS function to quickly play with this.
function getHTTPObject() {
  if (typeof XMLHttpRequest != 'undefined') {
    return new XMLHttpRequest();
  }
  try {
    return new ActiveXObject("Msxml2.XMLHTTP");
  } catch (e) {
    try {
      return new ActiveXObject("Microsoft.XMLHTTP");
    } catch (e) {}
  }
  return false;
}

window.onload = function()
{
  var http = getHTTPObject();
  if (http) {
    // You'll need to fill out url, user, and pass manually.

    // It breaks somewhere between this line and the next. It does
    // however correctly catch the Auth dialog. It just can't go
    // passed it.
    this.http.open("get", url, false, user, pass);
    this.http.send("");
    if (http.status == 200) {
      // do something as the url has been authed
    } else {
      alert("Incorrect username and/or password.");
    }
  } else {
    alert("Couldn't build HTTPObject.");
  }
}