NotSupportedException: ServicePointManager 不支持具有 https 方案的代理。
StackTrace:
   在 System.Net.ServicePointManager.FindServicePointHelper(Uri address, Boolean isProxyServicePoint)
   在 System.Net.ServicePointManager.FindServicePoint(Uri address, IWebProxy proxy, ProxyChain& chain, HttpAbortDelegate& abortDelegate, Int32& abortState)
   在 System.Net.HttpWebRequest.FindServicePoint(Boolean forceFind)
   在 System.Net.HttpWebRequest.set_InternalProxy(IWebProxy value)
   在 System.Net.HttpWebRequest.set_Proxy(IWebProxy value)
   在 System.Net.Http.HttpClientHandler.SetDefaultOptions(HttpWebRequest webRequest)
   在 System.Net.Http.HttpClientHandler.CreateAndPrepareWebRequest(HttpRequestMessage request)
   在 System.Net.Http.HttpClientHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
--- 引发异常的上一位置中堆栈跟踪的末尾 ---
   在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   在 DynamicClass.<SendAsyncRequest>d__3b.MoveNext()
--- 引发异常的上一位置中堆栈跟踪的末尾 ---
   在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   在 System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   在 System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)