This isn't really a Stack Overflow problem, but since you asked here I'll answer you here (next time, feel free to ping me on twitter @sqlfiddle or email me : admin at sqlfiddle dot com).
OpenID 2 (which is what I use currently at SQL Fiddle) is basically a dead technology. The current system I have is buggy and many of the providers I list aren't running any more.
I am in the midst of a complete re-write of the backend ( see progress here: https://github.com/jakefeasel/sqlfiddle2 ) which will switch this mechanism to use OpenID Connect instead. The good news is that this is the latest and greatest social login standard; the bad news is that there are not many Identity Providers (IDPs) currently running; basically, Google is the only general-purpose one that I have found.
I would really be happy if the fine folks here at StackExchange made an OpenID Connect IDP similar to what they have for the old OpenID 2 one, found here: https://openid.stackexchange.com/ . I think that could really help the adoption of this new and far better login protocol.