var parameters = new List<KeyValuePair<string, string>>
        {
            new KeyValuePair<string, string>("username","***"),
            new KeyValuePair<string, string>("password","***"),
            new KeyValuePair<string, string>("get","***")
        };

        var data = new FormUrlEncodedContent(parameters);

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://ekinobilet.ru/ekbs/upload.aspx");
        request.Method = "POST";

        byte[] dataArray = await data.ReadAsByteArrayAsync();
        request.ContentLength = dataArray.Length;
        request.ContentType = "multipart/form-data";

        var dataStream = await request.GetRequestStreamAsync();
        dataStream.Write(dataArray, 0, dataArray.Length);
        dataStream.Close();

        var resp = await request.GetResponseAsync();
        dataStream = resp.GetResponseStream();

        Stream receiveStream = resp.GetResponseStream();
        StreamReader readStream = new StreamReader(receiveStream, Encoding.UTF8);
        var responseText = readStream.ReadToEnd();

<error code="14"><![CDATA[Параметры "Имя пользователя" и "Пароль" должны быть указаны обязательно!]]></error>