Lol they're HTTPS on the login form but plain HTTP immediately after... what a joke? That invites people to do cred fishing on bigger LAN parties or conferences...
Yeah...you could just replace the HTTP landing page with your own containing your own login form.
It took me a minute of browsing around the site and then coming back here to ask, before I realized that you're saying they're redirecting httpS to PLAIN http. Wow.
I've actually seen it a few times myself but I don't have any examples offhand. My company's filter is lazy so it doesn't filter https traffic. Sometimes if I get a blocked site that's http I try the URL with https instead. Once in a while I get a redirect to http.