public static function fetchClient($client_id, $client_secret = null)
	{
		$query = DB::table('oauth_clients')->where('id', $client_id);
		if (null !== $client_secret) {
			$query->where('secret', $client_secret);
		}
		$client = $query->first();
		
		if (!$client) {
			return null;
		}
		
		return new Authentication\Client($client_id, (array) $client);
	}