/**
  * Initializes the authenticator with a key loader, auth header, and comparison timestamp.
  *
  * @param \Acquia\Hmac\KeyLoaderInterface $keyLoader
  *   A datastore used to locate secrets for corresponding IDs.
  * @param \Acquia\Hmac\AuthorizationHeaderInterface $authHeader
  *   An optional custom authorization header.
  * @param int $timestamp
  *   An optional custom timestamp by which to compare requests.
  */
 public function __construct(KeyLoaderInterface $keyLoader, AuthorizationHeaderInterface $authHeader = null, $timestamp = null)
 {
     parent::__construct($keyLoader);
     $this->authHeader = $authHeader;
     $this->timestamp = $timestamp ?: time();
 }