User.pm

package MyApp::Model::Session;

use Moose;
extend 'Catalyst::ApplicationModel';

has 'person' => (is=>'ro', required=>1, model=>'Schema::Person');

sub authenticate($self, $username='', $password='') {
  my $user = $self->person->authenticate($username, $password);
  $self->ctx->session->{user_id} = $user->id if !$user->has_errors;
  return $user; 
}

sub user($self) {
  return $self->ctx->stash->{user} ||= do {
    my $id = $self->ctx->session->{user_id} // return;
    my $person = $self->person->find({id=>$id}) // return;
  };  
}