(By the way, this was done with the Java version of Shindig. I
didn't try
the PHP version yet.)
See:
http://www.chabotc.com/opensocial/xrds-fetcher-tool-and-shindig-atom-support/
PHP version supports json & atom in & output formats, the current
batching protocol (which is bound to change soon) and everything else,
except for oauth.
Also using the XRDS document on www.partuza.nl you can also develop &
test your XRDS discovery:
http://www.chabotc.com/xrds-test.php?url=http://www.partuza.nl
Have fun !
-- Chris