R: [PHP] stupid crosscookie function

Please be patient.. but how does site 3 ask site 2 the ID of the user?: A. Site 3 can read the cookie on site 2. If so, site 3 can also read the cookie on site3 (of course, site 3 canonly read the cookie value not other info.. But If we get the cookie value, and if site1 stores referers and user info.. so site 3 can read them by querying site1--->> Why using the site between 1 and 3?) B. Site 3 cannot read the cookie on site 2. So how can site 2 (the middle one), know that user "foo" of site3 is the same as user "bar" of site1 and backchannel infoz? what a mess.. >That's correct. You can have pages at site1 and site3 that get a >cookied-image from site2, and site 2 can track activity across those sites >(look at the referrer, etc.), but site1 and site3 still can't read the >cookie directly. > >Where I've set up a cross-domain cookie server, the site that serves the >image has to be a proxy and hold the cookie on behalf of the other sites. >They can then exchange data through some back-channel (i.e. a common >database or request broker). > >For example: > >site1: > >... <img src="site2.com/setcookie.php?user=12345"> > >Site 2 sets a proxy cookie with info about user 12345 and stores info in a >database. > >If the user subsequently goes to site3, a page at site3 can ask site2 to >return the user associated with the cookie. > >I hope that's clear...it's been a looong day. :) > >It's an awkward process, but it's possible. > >- Tim >