Skipping the proxy cache based on a cookie?

[ehudros2]

Hi everyone,
I'm looking into setting up nginx as a proxy cache. I was wondering if
someone can elaborate a bit about ways to bypass the cache
in certain requests. For example, I'd like every new user to go to the
backend server once in order for some cookies to be written.
On further requests I'd like to serve the user with a cached copy of the
site.
How can I set a mechanism that bypasses the cache if a cookie with a
certain name does/does not exist?

Thanks!

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,161969,161969#msg-161969