Override laravel 4's authentication methods to use custom hasing function

This is how ended up solving the problem:

libraries\CustomHasherServiceProvider.php

use Illuminate\Support\ServiceProvider;

class CustomHasherServiceProvider extends ServiceProvider {

    public function register()
    {
        $this->app->bind('hash', function()
        {
            return new CustomHasher;
        });
    }

}

libraries\CustomHasher.php

class CustomHasher implements Illuminate\Hashing\HasherInterface {

private $NUMBER_OF_ROUNDS = '$5$rounds=7331$';


public function make($value, array $options = array())
{

    $salt = uniqid();
    $hash = crypt($password, $this->NUMBER_OF_ROUNDS . $salt);
    return substr($hash, 15);
}

public function check($value, $hashedValue, array $options = array())
{
    return $this->NUMBER_OF_ROUNDS . $hashedValue === crypt($value, $this->NUMBER_OF_ROUNDS . $hashedValue);
}

}

And then I replaced 'Illuminate\Hashing\HashServiceProvider' with 'CustomHasherServiceProvider' in the providers array in app/config/app.php

and added "app/libraries" to autoload classmap in composer.json

@vFragosop was on the right path with extending Auth.

There are a couple of ways to skin the cat and here is how I would do that without replacing the default Hasher class:

Include in your app/routes.php or wherever:

use Illuminate\Auth\Guard;
Auth::extend("eloquent", function() {
    return new Guard(
        new \Illuminate\Auth\EloquentUserProvider(new CustomHasher(), "User"),  
        App::make('session.store')
    );
});

Create and autoload a CustomHasher class (i.e., app/libraries/CustomHasher.php):

class CustomHasher extends Illuminate\Hashing\BcryptHasher {
    public function make($value, array $options = array())
    {
        ...
    }
    public function check($value, $hashedValue, array $options = array())
    {
        ...
    }
}

That's it.