I was trying to implement twitter sign in using OAuth (since this very same method should work on some other social networks too, such as yahoo). I've followed the instructions given at the official documentation and was getting 401 Unauthorized response all the time, I couldn't even get the oauth_token. Yet finally I found it. As a part of the OAuth request, there is a timestamp transferred. It must not be in the past. It can be years in the future, but not in the past. The OAuth protocol is Crap.
So we should see twitter and yahoo and maybe some others sign in options hopefully soon.
Why am I spending so much time on this? Actually the reason is that I am planing to make some of the features of this website for signed users only. Thus I need as many supported sign in providers as possible, to make life easier for everybody.