docs: public static String postPresignV4(String stringToSign, String secretKey, DateTime date, String region)
      throws NoSuchAlgorithmException, InvalidKeyException {
      Signer signer = new Signer(null, null, date, region, null, secretKey, null);
      signer.stringToSign = stringToSign;
      signer.setSigningKey();
      signer.setSignature();
  
      return signer.signature;
    }