I've been there. I can relate to everything you said!
The DHCP standard was such a waste of time. Ignore it completely, no client support whatsoever.
Intercepting all plain HTTP traffic (just drop https) and responding with a 30x redirect to your captive portal web page seems to be the ad-hoc "standard". Your captive portal domain can be served under secured HTTPS just fine.
I fully agree with the sandboxed browsers pain and absolute impossibility to get a nice consistent UX across platforms.
The DHCP standard was such a waste of time. Ignore it completely, no client support whatsoever.
Intercepting all plain HTTP traffic (just drop https) and responding with a 30x redirect to your captive portal web page seems to be the ad-hoc "standard". Your captive portal domain can be served under secured HTTPS just fine.
I fully agree with the sandboxed browsers pain and absolute impossibility to get a nice consistent UX across platforms.