[web2py] How to show user_id encrypted in the browser address bar and decrypt in the app?

[Constantine Vasil]

I am getting  user_id = str(auth.user.id), form a link to be clicked later.

When clicked on to the browser bar looks like like /user?user_id=9

That is insecure. How to encrypt it to look like /user?user_id=10iksmwu0 
(something like that)
and decrypt later when extracting from the request_vars?