The Open ID plugin is still giving me trouble with the latest Ruby-OpenID gem, 2.0.4. I fixed the issue I had with it, which was the a class name that changed from 1.x to 2.x.
OpenID::FilesystemStore should be OpenID::Store::Filesystem
OpenID::Store::Filesystem.new(OPEN_ID_AUTHENTICATION_DIR)
Also, root_url is still in there. According to the changelog DHH took it out. I safely moved it to a seperate function that defaults to the host if root_url isn't set.
def realm
root_url || "#{request.protocol + request.host_with_port}"
end