Pretty good. The only thing I'd suggest is in your AuthenticateInterface implementation lose the Facade and inject the actual guard instance.

Also the if statement isn't necessary in the auth function.

<?php
namespace Acme\Services;

use Acme\Interfaces\AuthenticateInterface as AuthenticateInterface;

class GuardAuthenticator implements AuthenticateInterface
{
	protected $authenticator;

	public function __construct(Guard $authenticator)
	{
		$this->authenticator = $authenticator;
	}

    public function auth($credentials)
    {
    	$credentials = [
    		'email' => $credentials['email'], 
    		'password' => $credentials['password']
    	];
        return $this->authenticator->attempt($credentials, true));
    }           
}