Rereading this I realize I didn't provide much context or frame the issue very well, and since I can't edit I'll post what the OP should have started with here.
From the pfSense Docs:
Captive Portal in pfSense software forces users on an interface to authenticate before granting access to the Internet. Where possible, the firewall automatically presents a login web page in which the user must enter credentials such as a username/password, a voucher code, or a simple click-through agreement.
Users have made many requests for something similar, but for authorizing access into the intranet, instead of out to the internet. This is often called a "reverse portal". This would be useful for e.g. setting up MFA for wireguard vpn connections or requiring login to access a different segment of the local network. Unfortunately, despite being nearly identical in implementation, netgate explicitly states that their captive portal feature is not capable of acting as a reverse portal, aka authorizing access to the local intranet.
One of the challenges with reverse portals is how to know when the user has disconnected and needs to reauthenticate. Here I propose a design where the user has to keep a browser tab with an open tcp connection (SSE with heartbeats) connected to the firewall to for the pass rule to be enabled; when the connection closes the pass rule is disabled and they will have to reauthenticate.
