http://internals.rust-lang.org/ does not redirect to https://internals.rust-lang.org/ at the moment. (But users.rust-lang.org does redirect.) I think this is recent, but perhaps not.
If you try GitHub login on HTTP, you get "Sorry, there was an error authorizing your account. Perhaps you did not approve authorization?", probably because URL does not match GitHub OAuth authorization.
I see all the things you describe too when not logged in.
When I'm already logged in it does redirect though.
Maybe @neil can help us understand what's going on.
I think I fixed the problem. It should always be redirecting to https now.
wfm. Thanks @neil!