Submission of
                            |
                     [login.tmpl] form
                            |
                   fires instance script 
                            |
                       [login.cgi] 
                            |
                        that calls 
                            |
                        [Login.pm] 
                            |
    which authenticates user and assigns the user's id to 
                            |    
        $self->session->param('user_id' => $user_id) 
                            |
                         and then
                            |
$self->redirects('admin.cgi'), an instance script which fires 
                            |
                        [Admin.pm]
                            |
                  which tries to retrieve
                            |
             $self->session->param('user_id')
                            |
                    which is undef'ed