Some further updates. I've given up on doing this in perl, we'll get further, faster in python, and there's a suggestion to integrate it with an app already written in python.

The python client identified in my earlier post cannot handle HTTPS and doesn't provide any useful response codes. This one does, although you'll need to manually install ssl support in python if you don't have it.

However, it provides the guts of a working WISPr routine in python, which could quickly be modified to accept credentials at command line, or doubtless the issue with the XML config file can be found and fixed. I have confirmed a successful login to BTWiFi using this code, although I have not yet gone live with it on my main phone.

The logic in this client is nice; it identifies the captive portal by the domain of the login URL, so if you're presented with a recognised login portal, regardless of the SSID that got you there, then the proper credentials will be selected. It also aborts graciously if we're already connected or there's no WISPr support, so I'd have no problem with running it on every connect. More testing is needed, and maybe a rewrite to use openssl which is more readily available in Maemo, but the guts of what we need is here.