So I have this: ini_set('session.cookie_domain', '.mydomain.com'); and it appears to be working just fine across abc.mydomain.com and xyz.mydomain.com. HOWEVER, it does NOT seem to be working with sub.abc.mydomain.com or sub2.xyz.mydomain.com. Will that work with sub-subdomains, or only the level one below it (subdomain)? Would really love to know if this is in fact the problem or I somehow have another problem lurking around!
You probabley have to enable it for each subdomain, that way their subdomains will be covered. Example: ini_set('session.cookie_domain', '.mydomain.com') will work for *.mydomain.com ini_set('session.cookie_domain', '.abz.mydomain.com') will work for *.abz.mydomain.com