ASP.NET and third party cookies

I'm working on a website that is merging with another company's site. My
site is ASP.NET based and will be running on a separate server. We
aren't going to allow access to my site unless the user has a certain
cookie set by the main site. I'm a little unsure of how to check this.

Their site is http://test.com/
My site will be http://mysite.test.com/

Do they just need to point DNS to my server for this to work? I know the
name of the cookie to check, but am unsure if I will be able to actually
read it from my server. What are the specifics for this? I believe there
is some sort of security in place for cookies, but am unsure of how it
works with third level domains. Any thoughts/documentation for doing
this?

Thanks,
Brian

===================================
This list is hosted by DevelopMentor®  http://www.develop.com

View archives and manage your subscription(s) at http://discuss.develop.com