Going back to "Captive Portal is made for Browser Based Auth only".
While this is perfectly true, browser communication in the end is just HTTP GET and HTTP POST requests.
If we would to capture a HTTP session between a, let's say Windows supported browser, and the IDA portal auth, with Fiddler or similar, and then extract and replicate the HTTP post of the authentication itself, and then script that into the linux cli box ?
Would this work ?
Afaik, Captive portal does not require any ongoing resources (keep-alive window open / cookies validation /etc) and once the IP and username have been linked on the FW side, it remains so until the configured session timeout.