Everyone with a smartphone or laptop has tried to access a public wireless network at least once and got an authentication page before proceeding with internet access—haven't you?

This method used to redirect a user trying to access the internet to an authentication page is a Captive Portal, which OPNsense has as a core feature. Captive Portals are usually used on guest networks Captive Portals are usually used on guest networks, such as airports and hotels' wireless networks hotspots, pay-as-you-go Wi-Fi guest networks, or even on wired networks in business centers.

OPNsense Captive Portal implementation

On OPNsense, the method used to redirect users is an HTTP redirect. Once the user tries to access a web page, a network address translation (NAT) rule will redirect it to a web service that runs the Captive Portal authentication page.

The following authentication methods are available through the OPNsense backend fabric: LDAP, RADIUS...