private async Task ConnectToGdaxFix()
    {
        _socketTcpClient = new TcpClient();
        _socketTcpClient.NoDelay = true;
        _bufferEnd = 0;
        await _socketTcpClient.ConnectAsync(_gdaxFixGateway, _gdaxFixPort);
        _sslStream = new SslStream(_socketTcpClient.GetStream());
        await _sslStream.AuthenticateAsClientAsync(_gdaxFixGateway);
        byte[] buffer = new byte[2048];
        var message = await FixSendLoginMessage();
        var bytes = await _sslStream.ReadAsync(buffer, 0, buffer.Length);
    }

    private async Task<string> FixSendLoginMessage()
    {
        var sendTime = DateTime.UtcNow.ToString("yyyyMMdd-HH:mm:ss.fff");
        string msgType = "A";
        var messageSeqNumber = (++messageSeqNum).ToString();
        var senderCompId = "apiKey";
        var targetCompId = "Coinbase";
        var password = "passphrase";
        var accessSign = CreateAccessSign(
                sendTime,
                msgType,
                messageSeqNumber,
                senderCompId,
                targetCompId,
                password
            );
        var logonMessage = $"98=0{'x01'}108=30{'x01'}554={password}{'x01'}96={accessSign}{'x01'}8013=Y";
        var headerAfter9Tag = $"35={msgType}{'x01'}34={messageSeqNumber}{'x01'}52={sendTime}{'x01'}49={senderCompId}{'x01'}56={targetCompId}";
        var length = logonMessage.Length + headerAfter9Tag.Length + 1;
        var messageHeader = $"8=FIX.4.2{'x01'}9={length}{'x01'}{headerAfter9Tag}";
        var messageWithHeader = $"{messageHeader}{'x01'}{logonMessage}";
        int sum = 0;
        int len = messageWithHeader.Length;
        for (int i = 0; i < len; i++)
        {
            sum += Convert.ToChar(messageWithHeader.Substring(i, 1));
        }
        sum = sum % 256;
        var messageWithChecksum = $"{messageWithHeader}{'x01'}10={sum.ToString("000")}{'x01'}";
        byte[] buffer = Encoding.ASCII.GetBytes(messageWithChecksum);
        await _sslStream.WriteAsync(buffer, 0, buffer.Length);
        return messageWithChecksum;
    }

    private string CreateAccessSign(
            string sendingTime,
            string msgType,
            string msgSeqNumber,
            string senderCompId,
            string targetCompId,
            string password
        )
    {
        var stringToHash = string.Join('x01', sendingTime, msgType, msgSeqNumber, senderCompId, targetCompId, password);
        var privateKeyAsBytes = Encoding.UTF8.GetBytes("privateKey");
        using (var hmac = new HMACSHA256(privateKeyAsBytes))
        {
            var signature = hmac.ComputeHash(Encoding.UTF8.GetBytes(stringToHash));
            return Convert.ToBase64String(signature);
        }
    }