public async Task <IActionResult> CallbackAsync(string state, string code)
        {
            _logger.LogInformation($"Process oAuth authorisation response and generate tokens.");
            try
            {
                _logger.LogInformation($"Exchanging token...code = {code} state = {state}");
                await _oAuthService.ExchangeAuthCodeForAuthToken(code);
            }
            catch (Exception ex)
            {
                _logger.LogError($"{ex.Message}, {ex.StackTrace}");
                var result = JsonConvert.SerializeObject(ex);
                return(Content(result));
            }

            return(new RedirectResult(state));
        }