Clearbits.net seems to fail for purely internal reasons. If you create a new account with an OpenID everything seems fine; the whole exchange works properly from our end so far as I can tell.
After a brief exchange with Andrew Arnott (author of dotNetOpenAuth), it was found that openid-consumer.appspot.com is non-compliant with the OpenID spec; claiming to sign fields it does not actually send. It is impossible to securely complete authentication, so we send them an error (the cause of the "Login cancelled" message).
We only really care to support well written OpenID relying parties, such as...
- Ourselves (more generally, anybody using dotNetOpenAuth semi-competently)