How do you set up an OpenID provider (server) in Ubuntu?

I want to log onto Stack Overflow using OpenID, but I thought I'd set up my own OpenID provider, just because it's harder :) How do you do this in Ubuntu?

Edit: Replacing 'server' with the correct term OpenID provider (Identity provider would also be correct according to wikipedia).

Solution

I personnally used phpMyID just for StackOverflow. It's a simple two-files PHP script to put somewhere on a subdomain. Of course, it's not as easy as installing a .deb, but since OpenID relies completely on HTTP, I'm not sure it's advisable to install a self-contained server...