I found that through dynamic scope user authentication can be an orthagonal concept in lisp, so I put out an earlier implementation of mine and here you go.
NOTE: I do not mean the special variable user-db
(let ((*user-db* (make-instance 'memory-db)))
(add "blub" "secret")
(assert-true (verify "blub" "secret"))
(assert-false (verify "blub" "wrong")))