WnsTokenAccessManager.cs

using System;
using System.Threading.Tasks;
using System.Net.Http;
using PushSharp.Core;
using System.Collections.Generic;
using Newtonsoft.Json.Linq;

namespace PushSharp.Windows
{
	public class WnsAccessTokenManager
	{
		Task renewAccessTokenTask = null;
		string accessToken = null;
		HttpClient http;

		public WnsAccessTokenManager(WnsConfiguration configuration)
		{
			http = new HttpClient();
			Configuration = configuration;
		}

		public WnsConfiguration Configuration { get; private set; }

		public async Task<string> GetAccessToken()
		{
			if (accessToken == null)
			{
				if (renewAccessTokenTask == null)
				{
					Log.Info("Renewing Access Token");
					renewAccessTokenTask = RenewAccessToken();
					await renewAccessTokenTask;
				}
				else
				{
					Log.Info("Waiting for access token");
					await renewAccessTokenTask;
				}
			}

			return accessToken;
		}

		public void InvalidateAccessToken(string currentAccessToken)
		{
			if (accessToken == currentAccessToken)
				accessToken = null;
		}

		async Task RenewAccessToken()
		{
			var p = new Dictionary<string, string> {
								{ "grant_type", "client_credentials" },
								{ "client_id", Configuration.PackageSecurityIdentifier },
								{ "client_secret", Configuration.ClientSecret },
								{ "scope", "notify.windows.com" }
						};

			var result = await http.PostAsync("https://login.live.com/accesstoken.srf", new FormUrlEncodedContent(p));

			var data = await result.Content.ReadAsStringAsync();

			var token = string.Empty;
			var tokenType = string.Empty;

			try
			{
				var json = JObject.Parse(data);
				token = json.Value<string>("access_token");
				tokenType = json.Value<string>("token_type");
			}
			catch
			{
			}

			if (!string.IsNullOrEmpty(token) && !string.IsNullOrEmpty(tokenType))
			{
				accessToken = token;
			}
			else
			{
				accessToken = null;
				throw new UnauthorizedAccessException("Could not retrieve access token for the supplied Package Security Identifier (SID) and client secret");
			}
		}
	}
}