WNS: Authentication token gets renewed only once

[es-alt]

What version of PushSharp are you using?

4.0.4

Describe your issue:

I have WNS broker running in process in the cloud. The broker is instantiated only once when the azure role starts and it runs uninterrupted for days. When a WNS authentication token expires, WnsAccessTokenManager will try to updated it only once.

Look at the code:

` 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;
    }`

"renewAccessTokenTask " will be null only for the first time.