private async void postRequest(string url)
    {
        using (HttpClient client = new HttpClient())
        {
            var values = new List<KeyValuePair<string, string>>();
            values.Add(new KeyValuePair<string, string>("case_type", "55"));
            values.Add(new KeyValuePair<string, string>("petname", "singh"));
            values.Add(new KeyValuePair<string, string>("year", "2016"));
            values.Add(new KeyValuePair<string, string>("button", "Submit"));

            var content = new FormUrlEncodedContent(values);

            var response = await client.PostAsync(url, content);
            var responseString = await response.Content.ReadAsStringAsync();

            using (StreamWriter post = new StreamWriter("post_website.txt"))
            {
                post.WriteLine(responseString);
            }
        }
    }