The hasher is bound to the IoC container as hash
, and can be resolved from the container using a couple of different methods. The method you use usually depends on where exactly you're extending the authentication layer.
To resolve the hasher from the container:
$hasher = App::make('hash');
$hasher = $app['hash'];
When extending auth the callback you supply should receive the application container as the first parameter. You can access the hasher using the second method described above.
Auth::extend('custom', function($app)
{
$hasher = $app['hash'];
return YourAuthProvider($hasher);
});