I'm working on an application that lets registered users create or upload content, and allows anonymous users to view that content and browse registered users' pages to find that content - this is very similar to how a site like Flickr, for example, allows people to browse its users' pages.
To do this, I need a way to identify the user in the anonymous HTTP GET request. A user should be able to type http://myapplication.com/browse/<userid>/<contentid> and get to the right page - should be unique, but mustn't be something like the user's email address, for privacy reasons.
Through Google App Engine, I can get the email address associated with the user, but like I said, I don't want to use that. I can have users of my application pick a unique user name when they register, but I would like to make that optional if at all possible, so that the registration process is as short as possible.
Another option is to generate some random cookie (a GUID?) during the registration process, and use that, I don't see an obvious way of guaranteeing uniqueness of such a cookie without a trip to the database.
Is there a way, given an App Engine user object, of getting a unique identifier for that object that can be used in this way?
I'm looking for a Python solution - I forgot that GAE also supports Java now. Still, I expect the techniques to be similar, regardless of the language.