public async Task<XeroOAuth2Token> RefreshToken(string clientId, Xero.NetStandard.OAuth2.Config.XeroConfiguration config)
        {
            var handler = new SocketsHttpHandler();
            var httpClient = new HttpClient(handler, false);
            //var xeroToken = TokenUtilities.GetStoredToken(); replace with DB read 
            var xeroToken = GetXeroToken(clientId);
            //var utcTimeNow = DateTime.UtcNow;
            var client = new XeroClient(config, httpClient);
            xeroToken = (XeroOAuth2Token)await client.RefreshAccessTokenAsync(xeroToken);
           // TokenUtilities.StoreToken(xeroToken); replace with DB store
            return xeroToken;
        }

using System.Net.Http;
var handler = new StandardSocketsHttpHandler();