I'm working with a third party company that will supply content for my site through a subdomain on my domain, but I'll be linking to their IP. They have to rebuild my header and footer on their end to make it somewhat seamless, but it's not perfect because the dynamic data in my header (unique to the logged in user) will be lost.

The rep I'm working with isn't a techy, so we're in a back and forth of me asking him if they can do something, then he has to go to the tech team and come back to me a few days later. I'm hoping to bypass that if you guys and gals can help me come up with a better solution.

So. If I set a cookie on my main page, then there's a subdomain pointing to a different IP, would they be able to include an Ajax script or IFRAME from the main domain that could read that cookie?

Meaning, the user goes to www.example.com, logs in, and I set a cookie with their username. Then they go to foo.example.com that's technically on a different server; could foo.example.com include an IFRAME or Ajax from www.example.com that reads the cookie that was set on www.example.com?