My service http://sociall.cc sends and receivesmessages from and to
more social networks like twitter, facebook, etc. I would like to add
a timed messages service where users could set messages to send in a
future time.

For this I need to have my own cake shell and run it by a crontask.

At a certain point I want to call

$this->requestAction('/messages/send');

But messages controller's send action is available if there is an
authenticated user.

So before I call this somehow the shell should authenticated itself as
a user. Than it could send the message, and the shell could
reauthenticate itself as a different user and send messages belongs to
that user.

The question is how could I authenticate the shell as a particular
user?