docs: public Map<String, String> presignedPostPolicy(PostPolicy policy)
      throws InvalidBucketNameException, NoSuchAlgorithmException, InsufficientDataException, IOException,
             InvalidKeyException, NoResponseException, XmlPullParserException, ErrorResponseException,
             InternalException, InvalidArgumentException {
      return policy.formData(this.accessKey, this.secretKey, getRegion(policy.bucketName()));
    }