getTask.wait（）方法调用中的系统聚合异常

Question

下面的代码是我编写的用于访问Identity服务以获取访问令牌作为响应（json响应）的代码。它是一个包含请求正文的帖子。 请求在json中，我希望我以相同的方式发送。 我在fiddler中用同一个身体尝试过这个请求，它运行正常。

请帮我识别错误。

public string GetClientIDFromIdentityService()
    {
        loggingService.Debug("GetClientIDFromIdentityService started");
        string url = strong textConfigurationManager.AppSettings["IdentityServiceEndPoint"].ToString();
        string IdentityServiceResponse = null;

        IdentityServiceRequest request = new IdentityServiceRequest();
        request.client_id = ConfigurationManager.AppSettings["ClientID"];
        request.grant_type = ConfigurationManager.AppSettings["GrantType"];
        request.scope = ConfigurationManager.AppSettings["Scope"];
        request.username = ConfigurationManager.AppSettings["UserName"];
        request.password = ConfigurationManager.AppSettings["Password"];
        string accessToken = "";
        try
        {
            using (var _client = new HttpClient())
            {
                var javaScriptSerializer = new JavaScriptSerializer();
                string jsonString = javaScriptSerializer.Serialize(request);

                HttpContent content = new StringContent(jsonString);
                _client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                var getTask = _client.PostAsync(url, content).ContinueWith((taskWithResponse) =>
                {
                    HttpResponseMessage response = new HttpResponseMessage();
                    response = taskWithResponse.Result;
                    var readTask = response.Content.ReadAsStringAsync();
                    readTask.Wait();
                    IdentityServiceResponse = readTask.Result;
                });
                getTask.Wait();

                JObject obj = JObject.Parse(IdentityServiceResponse);
                accessToken = obj["access_token"].ToString();
            }
        }
        catch (Exception ex)
        {
            loggingService.Error("Caught error at GetClientIDFromIdentityService Start", ex);
        }

        loggingService.Debug("GetClientIDFromIdentityService ended" + " AccessToken : " + accessToken);
        return accessToken;
    }