使用Rails从子域读取域的cookie

Question

In order to store some Google Analytics data, I would like to access to GA "__utmz" domain's cookie ( domain=.example.com ) from my www subdomain ( domain=www.example.com ). Is it possible to read this domain's cookie from a subdomain ? If yes, how can I do that with Rails ?

cookies[:__utmz] doesn't seem to work with all browsers.

I know I could configure my app setting the cookie domain to '.example.com' in my production.rb ( config.action_controller.session = { :domain => ".example.com" } ), but I'd rather not (because I don't want my www-subdomain's cookie to be shared among all subdomains).

I hope my question is clear enough...

Thanks by advance for your help (and sorry for the possible mistakes in my language...)

Answer 1

The only way to allow an app on subdomain.example.com to read a cookie from www.example.com would be for www.example.com to set a top-level example.com cookie.

This would allow subdomain.example.com to read it, but it would also allow every other subdomain of example.com to see this - which you said you don't want.

To follow this through - cookies are retrieved by name and scoped by the browser. If there are multiple cookies with the same name, you will have collisions. I believe the more generic example.com cookie will be the only one ever returned for subdomain.example.com if BOTH example.com and subdomain.example.com cookies exist.

TL;DR

Don't use top-level domain cookies unless you want the data to be the authoritative cookie across all domains (like single sign on). If you do this for Google Analytics you're going to collide on your different subdomains.