public function isValid(string $key) : bool
    {
        $key  = $this->getActualCacheKey($key);
        $meta = $this->getCacheContents()[$key] ?? [];

        if (empty($meta['expires_at'])) {
            return false;
        }

        return Carbon::now() < Carbon::createFromFormat(self::RFC_7231, $meta['expires_at']);
    }