BackendService.cs

if (result.HttpStatus == System.Net.HttpStatusCode.Unauthorized)
{
    /* 
     * The token has expired. Renew is auto-renew option
     * has been requested.
     */
    if (Permit != null && AutoTokenRenew)
    {
        if (ex.Call.Response.Headers.Contains("Token-Expired"))
        {
            Permit.UseRefreshToken();

            ResultSingle<Permit<UserT>> renewResult = await GetAsync(Permit,
                CreateRequest(Permit, true, data));

            if (renewResult.Code < 0)
                return result;

            UpdatePermit(renewResult);
        }
    }
    else
    {
        return result;
    }
}