Provided you are happy to depend on cookies just set a session cookie with the desired path and it will be delivered back to you when you hit that path. If you go to another subdomain you will get a different cookie/sessionID. If you want to set lots of session cookies, all globally accessible set the path as / (root) and they will all be available everywhere. You will then get all the sessid's for that user which can reference any data you care to set.