/**
  * Initializes the middleware with a key, realm, and custom auth header.
  *
  * @param \Acquia\Hmac\KeyInterface $key
  *   The key to sign requests with.
  * @param string $realm
  *   The API realm/provider.
  * @param array $customHeaders
  *   Custom headers to use in the signature.
  * @param \Acquia\Hmac\AuthorizationHeaderInterface $authHeader
  *   The custom authorization header.
  */
 public function __construct(KeyInterface $key, $realm, array $customHeaders, AuthorizationHeader $authHeader)
 {
     parent::__construct($key, $realm);
     $this->requestSigner = new MockRequestSigner($key, $realm, new Digest(), $authHeader);
 }