I know that Wordpress is stateless and doesn't use any global session variables, but when a user logs in via Wordpress, it must somehow keep track of who is logged in, right? Does Wordpress keep track of that in cookies?
I'm working on a plugin that must keep track of something similar. I can easily store some data in transients, but is there a unique identifier available that can identify a user, whether he or she is logged in to Wordpress or not? I would then use that to access the transient, for example.