I've noticed a couple of problems. If you got to the forum page directly via HTTP, the sign in button won't work. It just keeps looping. HTTPS fixes the problem. Coming from the Tech homage page brings you in via Https.
The second is that sometimes you're taken to a non-functional forum webpage for login. That usually happens when I click on a link that can't work if I'm not logged in. (An example is "view unread posts".) I that case, I don't log in but click the "Login" button which takes me to the functional single-signon page.
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