public Agent.Result SignResult (Agent.Result resut, string agentId) {
            string salt = CryptoUtils.RandomString(32);
            byte[] sign = null;
            if (RSASigner.Sign(Encoding.UTF8.GetBytes(salt + agentId + resut.SessionId), privateKey, out sign)) {
                resut.Sign = new Agent.sign_data() {
                    Salt = salt,
                    Sign = Convert.ToBase64String(sign)
                };
            } else {
                Log.Error(Ident, $"RSA sign failed for agent '{agentId}' session '{resut.SessionId}'");
            }
            return resut;
        }