code: public byte[] createSecret (PublicKeyCredentials pkcred, PrivateKey key, int length)
      {
          _data = new AuthResponseData();
          byte[] clientSecret = pkcred.getSecret(key);
          if (clientSecret == null) {
              _data.code = FAILED_TO_SECURE;
              return null;
          }
          byte[] secret = SecureUtil.createRandomKey(length);
          _data.code = StringUtil.hexlate(SecureUtil.xorBytes(secret, clientSecret));
          return secret;
      }
docs: Encodes the server secret in the response data, or sets the failed state.
  
  @return the server secret if successfully encoded, or null.