So far I've got varnish setting the header. I've got a solid handle on how to get the value from document.cookie, although I'm still wrapping my head around ipv6 compatibility.
Any feedback before I charge ahead? Am I barking up the wrong tree?
Cheers - Callum.
Keep in mind though, that varnish may not cache responses that have a Set-Cookie header. I don't know if this changes if varnish itself sets the header.