调试SharePoint API时出现“The SSL connection could not be established”错误求助

我在沙箱SharePoint站点开发文件管理工具，使用PnP.Framework和Microsoft.SharePointOnline.CSOM搭建控制台应用。前10分钟调试正常，之后执行ExecuteQuery()时抛出SSL连接错误，错误栈显示远程主机强制关闭了连接。

代码示例：

string clientId = "*********";
string redirectUrl = "http://localhost";
string tenantId = "************";
string siteUrl = "https://5klmt2.sharepoint.com/sites/TestTeam";

var authMan = PnP.Framework.AuthenticationManager.CreateWithInteractiveLogin(clientId, redirectUrl, tenantId);

using (ClientContext context = authMan.GetContext(siteUrl))
{
    var web = context.Web;
    context.Load(web, w => w.Id, w => w.Title);
    context.ExecuteQuery();

    Console.WriteLine($"{web.Id} - {web.Title}");

    var documents = web.GetListByTitle("Documents", l => l.Id, l => l.Title);

    Console.WriteLine($"{documents.Id} - {documents.Title}");
}

错误信息：

System.Net.WebException
  HResult=0x80131620
  Message=The SSL connection could not be established, see inner exception.
  Source=System.Net.Requests
  StackTrace:
   at System.Net.HttpWebRequest.GetResponse()
   at Microsoft.SharePoint.Client.SPWebRequestExecutor.Execute()
   at Microsoft.SharePoint.Client.ClientRequest.ExecuteQueryToServer(ChunkStringBuilder sb)
   at Microsoft.SharePoint.Client.ClientRequest.ExecuteQuery()
   at Microsoft.SharePoint.Client.ClientRuntimeContext.ExecuteQuery()
   at Microsoft.SharePoint.Client.ClientContext.ExecuteQuery()
   at Program.<TestStuff>d__1.MoveNext() in C:\Club Benchmarking\GitHub\SharePointCSOM\SharePointCSOM\Program.cs:line 29
   at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_1(Object state)
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()

Inner Exception 1:
HttpRequestException: The SSL connection could not be established, see inner exception.

Inner Exception 2:
IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host..

Inner Exception 3:
SocketException: An existing connection was forcibly closed by the remote host.

解决办法 #

• 更新依赖包到最新版本
  旧版本的PnP.Framework和CSOM库可能存在TLS握手、连接复用的已知bug，通过NuGet将所有相关包更新到最新稳定版，同步修复依赖组件的SSL相关问题。

• 强制指定TLS版本
  SharePoint Online要求使用现代TLS协议，在代码最开头添加强制声明，避免系统默认使用旧版本协议导致连接被拒：

  System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12 | System.Net.SecurityProtocolType.Tls13;
  

• 复用AuthenticationManager实例
  反复创建认证管理器可能导致连接池耗尽或会话冲突，尝试全局复用一个AuthenticationManager实例，而非每次请求都新建。

• 检查网络与代理配置
  企业网络下的代理服务器可能中断长连接，可切换到非企业网络测试；若必须使用代理，给ClientContext配置代理信息：

  context.Proxy = new WebProxy("http://your-proxy-address:port", true);
  

• 添加超时与重试机制
  临时网络波动可能导致连接断开，手动添加重试逻辑或调整请求超时时间：

  using (ClientContext context = authMan.GetContext(siteUrl))
  {
      context.RequestTimeout = 30000; // 设置30秒超时
      bool success = false;
      int retryCount = 0;
      while (!success && retryCount < 3)
      {
          try
          {
              var web = context.Web;
              context.Load(web, w => w.Id, w => w.Title);
              context.ExecuteQuery();
              success = true;
          }
          catch (WebException)
          {
              retryCount++;
              Thread.Sleep(1000 * retryCount);
          }
      }
  }
  

• 验证应用权限与会话有效性
  确认Azure AD中应用注册的权限（如Sites.Read.All）已被授予，且交互式登录的会话未过期，避免因权限或会话问题导致连接被强制关闭。

内容的提问来源于stack exchange，提问作者Brandon Armstrong