Async Download

DownloadAsync.cs

using System;
using System.IO;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Net.Http;

namespace ConsoleApplication
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine("Downloading page...");
            SaveWebsite();
            Console.WriteLine("Done.");
            Console.ReadLine();
        }

        static async Task<byte[]> DownloadPageAsync()
        {
            HttpClient client = new HttpClient();

            Uri page = new Uri("http://httpbin.org/post");

            Dictionary<string, string> credentials = new Dictionary<string, string> {
                {"firstname", "Test"},
                {"lastname", "User"}
            };

            FormUrlEncodedContent formCredentials = new FormUrlEncodedContent(credentials);

            HttpResponseMessage response = await client.PostAsync(page, content: formCredentials);
            byte[] contents = await response.Content.ReadAsByteArrayAsync();
            return contents;
        }

        private static async Task SaveWebsite()
        {
            byte[] contents = await DownloadPageAsync();
            File.WriteAllBytes(path: "/Users/william/Desktop/out.html", bytes: contents);
        }
    }
}