Im confused, don't the vast majority of public wifi spots use a some sort of custom web gui pop up so consistent programmatic access is difficult/impossible?
> custom web gui pop up
A captive portal.
Once you get proxy url as shown in the bash script, you can post to it whatever info they require (most of the time, it is just an email or zip code etc). The web gui pop up is just browser window opened by your OS. If you happen to use BSD/Linux, you are most likely will not see the popup. It is surely the case with OpenBSD.