This module implements a session engine for sessions stored entirely in
cookies. Usually only session id is stored in cookies and the session data
itself is saved in some external storage, e.g. database. This module allows
to avoid using external storage at all.

Since server cannot trust any data returned by client in cookies, this
module uses cryptography to ensure integrity and also secrecy. The data
your application stores in sessions is completely protected from both
tampering and analysis on the client-side.