public async Task AuthenticateUser(string userName, string password)
        {
            var fileName = $"BGG-{userName}-Auth.json"; // auth cache
            var options  = new JsonSerializerOptions {
                Converters = { new CookieConverter() }, WriteIndented = true
            };

            if (password != null)
            {
                Log.Info("Authenticating user");
                var cookies = await BggService.LoginUserAsync(userName, password);

                var json = JsonSerializer.Serialize(cookies, options);
                await File.WriteAllTextAsync(fileName, json);
            }
            else
            {
                var json = await File.ReadAllTextAsync(fileName);

                var cookies = JsonSerializer.Deserialize <IEnumerable <FlurlCookie> >(json, options);
                BggService.LoginUser(cookies);
            }
        }