# uses CGI::Application::Plugin::Forward and Authen.. etc
# you must know these by now..

sub break_a_leg : Runmode {
  my $self = shift;
  $self->__check or return $self->forward('error');
  # ... do whatever... 

}

sub __check {
  my $self = shift;
  $self->authen or die('no way.');
  $self->_my_sub_check_user_input() or return 0;
  return 1;
}