Hellbound,
it is not very easy to understand, what do you mean by 'It means having a hotspot login page'.
HotSpot provides embedded proxy for the clients, if you need to setup proxy that can be used for non-HotSpot clients, you have to disable transparent-proxy for HotSpot, and setup web-proxy on the routers. Access list or firewall might be used as filtering option for clients.
Let me put it this way:
hotspot package in routeros authenticate users who are allowed to send/receive traffic to internet.
webproxy is caching web content for those users and it runs on local IP addresses or even external IP address.
if it is not blocked in firewall filter, your web-proxy service can be accessed from anyone outside your network (from internet) to relay traffic for spam and web surfing and etc.
what I am doing at this moment is blocking any request from outside to access my webproxy server.
what I like to do is to authenticate who is allowed to access webproxy server from outside network and who is not.
hotspot is working based on MAC and cookie, is it possible to bind hotspot to web-proxy and redirect outsiders who access webproxy server to hotspot login page, once they are authenticated they'll be redirected to their visiting page.
thanks