public static string TokenIsValid(HttpRequestMessage req, bool useKeyVault, string appSettingExtCert, string ExtCertKey, TraceWriter log)
        {
            string issuedToken = Helpers.GetUserTokenInRequest(req);

            var tokenuserId = string.Empty;

            if (useKeyVault)
            {
                string extCert = Helpers.GetKeyVaultSecretValue(ExtCertKey, log);
                tokenuserId = CheckVSTSToken.checkTokenValidityV2(issuedToken, extCert);
            }
            else
            {
                string extcert = appSettingExtCert;
                tokenuserId = CheckVSTSToken.checkTokenValidity(issuedToken, extcert);
            }

            return(tokenuserId);
        }