读取 EWS 文件夹时出现 Microsoft.Exchange.WebServices.Data.ServiceRequestException

Question

I'm a newbie to C# development

I'm trying to migrate the EWS authentication from basic authentication to OAuth2 authentication.

#Implementation

using System;
using System.Net;
using System.Threading.Tasks;
using Microsoft.Exchange.WebServices.Data;
using Microsoft.Identity.Client;



namespace DataLoadLibrary.Email
{
    public class OAuthTokenProviders
    {


        public static async Task<OAuthTokenProviders> Create()
        {
            var myClass = new OAuthTokenProviders();
            await myClass.Initialize();
            return myClass;
        }

        private OAuthTokenProviders()
        {
            Console.WriteLine("TESTING INSIDE CONSTRUCT");

        }


        
        private async System.Threading.Tasks.Task Initialize()
        {
            Console.WriteLine("TESTING");
            // Using Microsoft.Identity.Client
            var cca = ConfidentialClientApplicationBuilder
                .Create("")      //client Id
                .WithClientSecret("")
                .WithTenantId("")
                .Build();
            var ewsScopes = new string[] { "https://outlook.office365.com/.default" };
            try
            {
                // Get token
                var authResult = await cca.AcquireTokenForClient(ewsScopes)
                    .ExecuteAsync();
                // Configure the ExchangeService with the access token
                var ewsClient = new ExchangeService(ExchangeVersion.Exchange2013_SP1);
                ewsClient.Url = new Uri("https://outlook.office365.com/EWS/Exchange.asmx");
                ewsClient.Credentials = new OAuthCredentials(authResult.AccessToken);
                ewsClient.ImpersonatedUserId =
                    new ImpersonatedUserId(ConnectingIdType.SmtpAddress, "");
                //Include x-anchormailbox header
                ewsClient.HttpHeaders.Add("X-AnchorMailbox", "");
                // Make an EWS call to list folders on exhange online

                var folders = ewsClient.FindFolders(WellKnownFolderName.MsgFolderRoot, new FolderView(10));
                foreach (var folder in folders)
                {
                    Console.WriteLine($"Folder: {folder.DisplayName}");
                }
                // Make an EWS call to read 50 emails (last 5 days) from Inbox folder
                TimeSpan ts = new TimeSpan(-60, 0, 0, 0);
                DateTime date = DateTime.Now.Add(ts);
                SearchFilter.IsGreaterThanOrEqualTo filter = new SearchFilter.IsGreaterThanOrEqualTo(ItemSchema.DateTimeReceived, date);
                var findResults = ewsClient.FindItems(WellKnownFolderName.Inbox, filter, new ItemView(50));
                foreach (var mailItem in findResults)
                {
                    Console.WriteLine($"Subject: {mailItem.Subject}");
                }
                EmailMessage email = new EmailMessage(ewsClient);
                email.ToRecipients.Add("");
                email.Subject = "HelloWorld";
                email.Body = new MessageBody("This is a test email using MS Exchg we services");
                email.Send();
            }
            catch (MsalException ex)
            {
                Console.WriteLine($"Error acquiring access token: {ex}");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error: {ex}");
            }
            if (System.Diagnostics.Debugger.IsAttached)
            {
                Console.WriteLine("Hit any key to exit...");
                Console.ReadKey();
            }
        }


    }
}

Using the above implementation am able to get the access token successfully. However when am listing the folder in the mailbox, getting below exceptions

Microsoft.Exchange.WebServices.Data.ServiceRequestException
  HResult=0x80131500
  Message=The request failed. The underlying connection was closed: An unexpected error occurred on a send.
  Source=Microsoft.Exchange.WebServices
  StackTrace:
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest(IEwsHttpWebRequest& request)
   at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
   at Microsoft.Exchange.WebServices.Data.ExchangeService.InternalFindFolders(IEnumerable`1 parentFolderIds, SearchFilter searchFilter, FolderView view, ServiceErrorHandling errorHandlingMode)
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindFolders(FolderId parentFolderId, FolderView view)
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindFolders(WellKnownFolderName parentFolderName, FolderView view)
   at DataLoadLibrary.Email.OAuthTokenProviders.<Initialize>d__2.MoveNext() in C:\Users\path\to\file\DataLoadLibrary\Email\OAuthTokenProviders.cs:line 51

  This exception was originally thrown at this call stack:
    [External Code]

Inner Exception 1:
WebException: The underlying connection was closed: An unexpected error occurred on a send.

Inner Exception 2:
IOException: Authentication failed because the remote party has closed the transport stream.

I would want to know how to solve the exception. Thanks in Advance

Answer 1

Message=The request failed. The underlying connection was closed: An unexpected error occurred on a send.

That error is generally related to TLS as Office365 require at least TLS 1.2 to be used. Generally the best way of solving this is through the following reg entry https://learn.microsoft.com/en-us/officeonlineserver/enable-tls-1-1-and-tls-1-2-support-in-office-online-server#enable-strong-cryptography-in.net-framework-45-or-higher this will mean .net will use the strongest version available. Otherwise you can force it in the code using

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