I am writing a webapp on Google App Engine with python and right now I am using the built in federated login system with OpenID and it works great with Google/Yahoo/AOL but I want to give users on Facebook and Twitter access to the site as well. There have been questions like this in the past year or two but none have been fully answered or are out of date.
Basically all I want is for the user to be able to login with either of these three services and I want to be able to authenticate them and store a unique user_id along with each user. I am not all that interested in posting to facebook walls or sending tweet updates from the site I simply want to give users a really easy way to login with existing accounts.
Have you thought of using a library that provides this functionality? Something like simpleauth:
Most of the boilerplate for new projects have this stuff built in too: