trait S3fsCorsSignatureTrait in S3 File System CORS Upload 7

trait S3fsCorsSignatureTrait {

  /** @var array Cache of previously signed values */
  private $cache = [];

  /** @var int Size of the hash cache */
  private $cacheSize = 0;
  private function createScope($shortDate, $region, $service) {
    return "{$shortDate}/{$region}/{$service}/aws4_request";
  }
  private function getSigningKey($shortDate, $region, $service, $secretKey) {
    $k = $shortDate . '_' . $region . '_' . $service . '_' . $secretKey;
    if (!isset($this->cache[$k])) {

      // Clear the cache when it reaches 50 entries
      if (++$this->cacheSize > 50) {
        $this->cache = [];
        $this->cacheSize = 0;
      }
      $dateKey = hash_hmac('sha256', $shortDate, "AWS4{$secretKey}", true);
      $regionKey = hash_hmac('sha256', $region, $dateKey, true);
      $serviceKey = hash_hmac('sha256', $service, $regionKey, true);
      $this->cache[$k] = hash_hmac('sha256', 'aws4_request', $serviceKey, true);
    }
    return $this->cache[$k];
  }

}