problems authenticating an ajax request

problems authenticating an ajax request

Hello all,
I'm trying to send an ajax request which should authenticate via basic http authentication.
In the jQuery.ajax() documentation page (http://api.jquery.com/jQuery.ajax/) it states that there are two options, "username" and "password" that can be specified, and that they are going "to be used in response to an HTTP access authentication request."
I set those two options in my request, but I cannot see any "Authorization: Basic xxx" header being send by jquery.
this is my code:

  $.ajax( {
    cache: false,
    url: 'http://...',
    type: 'GET',
    dataType: 'xml',
    username: 'username',
    password: 'password',
    success: function(xml) {
        // ...
    }
  });

I have see that a lot of people suggest to use the beforeSend hook and set the Authorization header manually (using setRequestHeader()) but I really want to avoid this.