Try to patch Ajax.Request
like this:
Ajax.Request.prototype.request = Ajax.Request.prototype.request.wrap(function(request, url) {
if (this.options.withCredentials) {
this.transport.withCredentials = true;
}
request(url);
});
And then you'll have additional option withCredentials
:
new Ajax.Request('example.com', {
withCredentials: true
});