protected override async Task <HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { var token = await _helper.AcquireTokenSilentAsync(); if (string.IsNullOrWhiteSpace(token)) { return(new HttpResponseMessage(HttpStatusCode.Unauthorized)); } request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token); return(await base.SendAsync(request, cancellationToken)); }