minimal HTTP GCM application server in C#

GoogleCloudMessagingApplicationServer.cs

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

namespace Siliconbrain.Utilities
{
    public class GoogleCloudMessagingApplicationServer : IDisposable
    {
        private static readonly Uri _sendUri = new Uri("https://android.googleapis.com/gcm/send");

        private readonly HttpClient _httpClient;

        public GoogleCloudMessagingApplicationServer(string apiKey)
            : this(SetAuthorization(new HttpClient(), apiKey))
        {
        }

        public GoogleCloudMessagingApplicationServer(HttpClient httpClient)
        {
            _httpClient = httpClient;
        }

        static HttpClient SetAuthorization(HttpClient httpClient, string apiKey)
        {
            var success = httpClient.DefaultRequestHeaders.TryAddWithoutValidation("Authorization", "key=" + apiKey);

            System.Diagnostics.Debug.Assert(success);

            return httpClient;
        }

        public async Task SendMessageAsync<TMessageData>(IEnumerable<string> registrationIds, TMessageData messageData)
        {
            var requestBody = new
            {
                registration_ids = registrationIds,
                data = messageData,
            };

            await _httpClient.PostAsJsonAsync(_sendUri, requestBody);
        }

        public void Dispose()
        {
            _httpClient.Dispose();
        }
    }
}