Securing classic asp ajax call

[SJshah]

I need to be able to add javascript to an existing classic asp page that does an ajax query to a service a remote service. My theory is that the javascript would call a proxy asp page that would actually call the service (to hide the actual url called). How can I ensure that the proxy can only be called from the specific page?The existing page is part of a site that's not on our server, so no changes can be made to IIS, etc.AmendmentI'm adding a button to the 'Enter Address' page of an e-commerce service's site (this is in Classic ASP). The button executes a query to obtain details from a web service.