Multisite (MultiWP) – Single Sign on in 2.6

Is it possible to get cookies to behave in such a way as to allow one login to take effect across a whole domain?

I have been trying to get this to work for some time now. I have:

– ensured that AUTH_KEY, SECURE_AUTH_KEY, LOGGED_IN_KEY, LOGGED_IN_SALT, AUTH_SALT and SECRET_KEY are identical accross all installs
– define(‘COOKIE_DOMAIN’, ”);
– define(‘COOKIEPATH’, ‘/’);

in addition I have also tried:

– define(‘COOKIE_DOMAIN’, ‘.mydomain.com’);
– made db entry wp_options.secret the same accross all installs

The cookie keys and values that wordpress creates seem to always have a unique, per install value which is a very long garbled code.

I get the feeling that if i could get all my installs to create this same code, single sign on will work (I may be wrong). However, I can’t find how WP creates these unique codes. No matter how I try to make my installs identical, they insist on having unique cookies.

Can anybody shed any light on this? It’s doing my head in!