ReviewR.Web.Services.Authenticators.GoogleAuthenticator.VerifyToken C# (CSharp) Method

        public override Task<string> VerifyToken(string appId, string accessToken)
        {
            HttpClient client = CreateHttpClient();
            return client.GetAsync("https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=" + accessToken).Then(resp =>
            {
                resp.EnsureSuccessStatusCode();
                return resp.Content.ReadAsStringAsync();
            }).Then(content =>
            {
                dynamic response = JObject.Parse(content);
                if (response.error == "invalid_token" ||
                    response.audience != appId)
                {
                    return (string)null;
                }
                else
                {
                    return accessToken;
                }
            });
        }