Authenticate to Wunderlist

WunderlistHelper.cs

public class WunderlistHelper
{
    private static Template10.Services.NetworkAvailableService.NetworkAvailableService _NetworkService = new NetworkAvailableService();
    private static Template10.Services.SecretService.SecretService _SecretService = new SecretService();
    private static Template10.Services.HttpService.HttpHelper _HttpHelper = new HttpHelper();
    private WunderlistSettings _settings;

    public WunderlistHelper(WunderlistSettings settings)
    {
        _settings = settings;
    }

    string Token
    {
        get { return _SecretService.ReadSecret(GetType().ToString(), nameof(Token)); }
        set { _SecretService.WriteSecret(GetType().ToString(), nameof(Token), value); }
    }

    bool IsConnected => _NetworkService.IsInternetAvailable().Result;

    public async Task<bool> AuthenticateAsync()
    {
        // https://developer.wunderlist.com/documentation/concepts/authorization

        if (!IsConnected)
        {
            return false;
        }

        var code = await GetCodeFromUserAsync();
        if (string.IsNullOrEmpty(code))
        {
            return false;
        }

        var token = Token = await GetTokenFromCodeAsync(code);
        if (string.IsNullOrEmpty(token))
        {
            return false;
        }

        SetupAuthHeaders();
        return true;
    }

    private async Task<string> GetCodeFromUserAsync()
    {
        var state = Uri.EscapeUriString(Guid.NewGuid().ToString());
        var client_id = Uri.EscapeUriString(_settings.CLIENT_ID);
        var redirect_uri = Uri.EscapeUriString(_settings.AUTH_CALLBACK_URL);
        var getCodeUri = new Uri($"https://www.wunderlist.com/oauth/authorize?client_id={client_id}&redirect_uri={redirect_uri}&state={state}");
        var callbackUri = new Uri(_settings.AUTH_CALLBACK_URL);

        WebAuthenticationResult response = null;
        try
        {
            response = await WebAuthenticationBroker.AuthenticateAsync(WebAuthenticationOptions.None, getCodeUri, callbackUri);
        }
        catch (Exception)
        {
            return string.Empty;
        }

        switch (response.ResponseStatus)
        {
            case WebAuthenticationStatus.UserCancel:
            case WebAuthenticationStatus.ErrorHttp:
                return string.Empty;
        }

        var responseData = response.ResponseData.ToString();
        var responseQuerystring = new Uri(responseData).QueryString();
        var correlationState = responseQuerystring.GetFirstValueByName("state");
        if (correlationState != state)
        {
            return string.Empty;
        }

        return responseQuerystring.GetFirstValueByName("code");
    }

    private async Task<string> GetTokenFromCodeAsync(string code)
    {
        var requestObject = new
        {
            client_id = _settings.CLIENT_ID,
            client_secret = _settings.CLIENT_SECRET,
            code = code,
        };
        var requestJson = JsonConvert.SerializeObject(requestObject);
        var requestContent = new HttpStringContent(requestJson,
            Windows.Storage.Streams.UnicodeEncoding.Utf8, "application/json");

        var requestUri = new Uri($"https://www.wunderlist.com/oauth/access_token");
        var response = await _HttpHelper.Client.PostAsync(requestUri, requestContent);
        if (!response.IsSuccessStatusCode)
        {
            return string.Empty; // <-- always a 422
        }

        var responseJson = await response.Content.ReadAsStringAsync();
        dynamic responseModel = JsonConvert.DeserializeObject(responseJson);
        return responseModel.access_token;
    }

    private void SetupAuthHeaders()
    {
        var httpClientHeaders = _HttpHelper.Client.DefaultRequestHeaders;

        var clientKey = "X-Client-ID";
        if (httpClientHeaders.ContainsKey(clientKey)) httpClientHeaders[clientKey] = _settings.CLIENT_ID;
        else httpClientHeaders.Add(clientKey, _settings.CLIENT_ID);

        var tokenKey = "X-Access-Token";
        if (httpClientHeaders.ContainsKey(tokenKey)) httpClientHeaders[tokenKey] = Token;
        else httpClientHeaders.Add(tokenKey, Token);
    }
}

public class WunderlistSettings
{
    // https://developer.wunderlist.com/apps

    public string CLIENT_ID { get; set; }
    public string CLIENT_SECRET { get; set; }
    public string APP_URL { get; set; }
    public string AUTH_CALLBACK_URL { get; set; }
}