Try opening the console tools of your browser, find the network tab, then log in (you should be able to get the captive portal in your browser if you experiment

Try opening the console tools of your browser, find the network tab, then log in (you should be able to get the captive portal in your browser if you experiment a bit, kinda as per the article.) Then locate the request that was made when you logged in, right click, and “Copy as cURL.” Then just paste the resulting command in a terminal when needed. It should capture everything you need (notwithstanding CSRF/session IDs rotating etc.)