internal string ToAskMessage()
        {
            var buttonValue = string.Empty;

            if (Button1 != null)
            {
                buttonValue += "~" + Button1.ToAskMessage();
            }

            if (Button2 != null)
            {
                buttonValue += "~" + Button2.ToAskMessage();
            }
            return(Base64UrlTextEncoder.Encode(Encoding.ASCII.GetBytes(Message)) + buttonValue);
        }