When a captive portal is enabled on a network, users attempting to access the network from a desktop/laptop computer or mobile device are first directed to a web page. Although captive portals can be enabled on wired networks, more typically they are used as gatekeepers on wireless networks.
Captive portal pages are displayed after a user connects to a network protected by a captive portal. The user then will try to access a URL. If the URL request comes from an unknown client, the network operating system—in this case, pfSense/FreeBSD—will recognize that users must pass through the captive portal before they have full access to the network.
The user will be redirected to a web page or splash screen. They may simply have to click on a button to indicate their agreement with the network's terms of service or an End User License Agreement...