I'd like to share with you pubcookie authentication module that I've developed not a long time ago. I think there's no need to write about the advantage of using pubcookie SSO.
The module works with Moodle versions 1.8 and 1.9. I am attaching the module source to this message.
Please read the module documentation before installation, or you may lock yourself out of your moodle site. Here are links to the documentation:
Module was developed as a part of iEARN project.
Feel free to post your comments.