Where to get started with GWT and Federated login? (php only)

I'm interested in adapting my site to work with a federated login
system.
(you can see a beta of my site here to get the general idea;
http://www_rateoholic.co.uk/test/Rateoholic/main/Rateoholic_Frame.html#titlepage
)

Ive looked over the;
http://code.google.com/apis/accounts/docs/OpenID.html
pages and I see a wealth of helpfull information and advice. But to be
honest its overwealming me and I really dont know where to get
started.

My requirements are;
1. Has to be PHP/GWT based...my server cant use servlets.
2. Not worried about getting other user data, just a login will do.
3. thats it really.

Can someone help put me on the best road to get started? Is there any
gwt/php based methods established already?