What you might not be as familiar with is that these authentication sites often block you from visiting any domain at all, and then to access the authentication

What you might not be as familiar with is that these authentication sites often block you from visiting any domain at all, and then to access the authentication site on their own domain you must explicitly link their domain to an IP address through the /etc/hosts file.³ 3. I'm assuming on Mac and Windows this is taken care of for you somehow and it is a non-problem. I... have never had to do this in any distro or OS (NixOS, Arch, macOS at least). The way I've found captive portals to work in practice is that when I connect to the WiFi, my computer gets the captive portal's DNS server through DHCP, and their DNS server points any and every website to the IP address of the captive portal. To make it even easier, Firefox checks "detectportal.firefox.com" every so often to see whether or not there's a captive portal, and gives me a prompt to log in to it if need be.