Comment by deathanatos

Dumb captive portals, which do still exist in some places, usually do MitM attacks on the connection, so you need some http(no-s) site that you can abuse as "yeah, this can get attacked by the WiFi" to then answer the portal.

The right way is that there's DHCP option for the network to signal "I have a captive portal", that's been standardized for over a decade.

… or … IDK … just stop shoving ads down people's throats just because they want WiFi.