Hi Graham, we investigated OpenID and we found several issues. First, website owners have been complaining about it, see:
http://blog.wekeroad.com/thoughts/open-id-is-a-party-that-happenedhttp://news.ycombinator.com/item?id=1915588Besides that, we really tried to implement it. The first information OpenID must give to Nabble is the email of the user. Not all providers give this information, which is pointless to Nabble because we would have to request the emails anyways in the registration page. So we cannot generally accept OpenID on Nabble. But we started looking into Google and Facebook because they provide the email of the user and this integration could possibly work. In fact, it was quite easy to integrate these services with Nabble, until we tested embedding and custom domain names. Nabble has a complex login mechanism for embedding and only Google was able to work with it. On the other hand, Facebook requires a fixed domain to send/receive requests, so custom domains don't work. In summary, Google is probably the only OpenID provider that can work smoothly with Nabble. Since you originally requested generic OpenID, I am not sure Google will satisfy your needs. Unfortunately, that's the only service we could offer for now. Please let me know what you think.