Hello.
That's not secret that many people use web-proxy like small web server, you can just deny access to all and edit error.html page.

But that's only one page and often more than one needed.

Right now you can specify multiply ports for web-proxy. It may use in conditions inside error.html: if it's 8080 port, show "no money" page, if it's 8081 port, show "blocked by laws" page, etc.
But there is no predefined variable $(port) in error.html.

Also, it can be very nice if you add variables $(user-ip) for IP address from which came the request (it can be used for ajax loading info about subscriber, e.g his account balance), and editable $(http-status), $(http-header) like in Hotspot.