How do I implement an OpenID consumer in my Google App Engine project?

Question

I want to use OpenID in my Java Google App Engine web application but I don't know where to start...

I have looked at openid4java and joid.

openid4java says you have to place some libraries on the "endorsed libraries"-path. I don't have one locally on my computer, and I sure don't know how to do that on Google App Engine.

joid looks simple enough but doesn't look up to date or something because I get a HTTP 400 back from Google when I try to get an authentication.

Any pointers?