gistfile1.pl

use Plack::Builder;

my $old_app = sub {
  return sub {
    my $respond = shift;
    $respond->([200, [], ['success']]);
  }
};

sub delayed_auth {
  my ($env, $cb) = @_;
  # ... AE::DBI query
  $cb->(1);
}

sub {
  my $env = shift;

  return sub {
    my $respond = shift;

    delayed_auth($env, sub {
      my $success = shift;
      $respond->($success ? $old_app->($env) : [401, [], []]);
    });

  };
};