protected override async Task <HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken ct)
        {
            // Get authorization token from Azure AD.
            var authenticationResult = await _clientApplication.AcquireTokenForClientAsync(Scopes);

            // Set authorization token on request.
            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", authenticationResult.AccessToken);

            return(await base.SendAsync(request, ct));
        }