Not sure why you're doing it but one way you could implment this is through document events. On document open go to a location for authentication (Windows, XML, or DB), return the results, if user is ok then you're done otherwise inform user and close down document.
I usually implement something like that in an extension. But you are not going down that path. What about embedding VBA code into your document to hook into the document event? The downside is you now have to distribute that map document to all your users.