How do providers do it?

Question

Computer networks

According to the IPoE pseudo-protocol, we are given a dhcp address, but access to the Internet is made only after the mac-address of the equipment is bound. In this case, we observe that in the browser, when you go to any site, you are prompted to enter the username and password of the subscriber. The question is, how is it implemented?

Answer 1

At the beginning, when the IP is not authorized, all http requests from it are directed by the firewall to its web server, which issues an authorization page.
After authorization, the firewall is told to route normally.

Answer 2

And if a person opens HTTPs?