Exchange Online EWS调用返回无效XML错误排查求助

问题描述 #

我使用以下代码通过OAuth认证Exchange Online（Exchange 365）服务器并发送邮件，但收到错误提示："The response received from the service didn't contain valid XML"。已参考官方文档配置，Entra应用设置正确。

代码示例 #

using System.Diagnostics;
using Microsoft.Exchange.WebServices.Data;
using Microsoft.Identity.Client;
using Task = System.Threading.Tasks.Task;

namespace My.Sandbox.CoreConsoleApp;

internal class Program
{
    // ReSharper disable once IdentifierTypo
    private const string MyEntraAppClientId = "client-id";

    // ReSharper disable once IdentifierTypo
    private const string MyEntraAppTenantId = "tenant-id";
    private const string MyClientSecretValue = "client-secret-value";

    // ReSharper disable once IdentifierTypo
    private const string MyEntraAppRedirectUri = "https://login.microsoftonline.com/common/oauth2/nativeclient";
    private const string Outlook365EndpointUrl = "https://outlook.office365.com/EWS/Exchange.asmx";

    /// <summary>
    ///     Specifies the primary mailbox against which operations should be performed. Useful in scenarios involving
    ///     multiple mailboxes or delegate access. Ensures accurate handling of tasks by directing requests
    ///     to the intended mailbox, facilitating secure and contextually relevant operations within Exchange environments.
    /// </summary>
    // ReSharper disable once InconsistentNaming
    // ReSharper disable once IdentifierTypo
    private const string Headers_XAnchormailbox = "X-AnchorMailbox";

    private static void Main(string[] args)
    {
        Task.Run(() => ConnectUsingAppOnlyAuthentication("my-email-address@My2.onmicrosoft.com")).Wait();
    }

    private static async Task ConnectUsingAppOnlyAuthentication(string accountAddress)
    {
        try
        {
            var authResult = GetToken();

            // Configure the ExchangeService with the access token
            var ewsClient = new ExchangeService
            {
                Url = new Uri(MyEntraAppRedirectUri),
                Credentials = new OAuthCredentials(authResult.AccessToken),
                ImpersonatedUserId =
                    new ImpersonatedUserId(ConnectingIdType.SmtpAddress, accountAddress)
            };

            // ReSharper disable once CommentTypo
            //Include x-anchormailbox header
            ewsClient.HttpHeaders.Add(Headers_XAnchormailbox, accountAddress);

            var email = new EmailMessage(ewsClient);
            email.ToRecipients.Add("test-target-email@gmail.com");
            email.Subject = "HelloWorld";
            email.Body = new MessageBody("This is the first email I've sent by using the EWS Managed API.");
            await email.SendAndSaveCopy();
        }
        catch (MsalException ex)
        {
            Console.WriteLine($"Error acquiring access token: {ex}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex}");
        }

        if (Debugger.IsAttached)
        {
            Console.WriteLine(@"Hit any key to exit...");
            Console.ReadKey();
        }
    }

    private static AuthenticationResult GetToken()
    {
        // Using Microsoft.Identity.Client 4.22.0
        var applicationBuilder = ConfidentialClientApplicationBuilder
            .Create(MyEntraAppClientId)
            .WithClientSecret(MyClientSecretValue)
            .WithTenantId(MyEntraAppTenantId)
            .Build();

        // The permission scope required for EWS access
        var ewsScopes = new string[] { Scope.Outlook365_Default.Value };

        // Make the token request
        return applicationBuilder.AcquireTokenForClient(ewsScopes).ExecuteAsync().Result;
    }

    /// <summary>
    ///     Represents an OAuth scope, which determines the resources and application can access
    ///     and the actions it can perform.
    /// </summary>
    [DebuggerDisplay("{Value}")]
    internal class Scope
    {
        #region constructors

        private Scope(string value)
        {
            Value = value;
        }

        #endregion

        #region properties

        public string Value { get; }

        #endregion

        #region static members

        // ReSharper disable once InconsistentNaming
        public static readonly Scope Outlook365_Ews_AccessAsUser_All =
            new("https://outlook.office365.com/EWS.AccessAsUser.All");

        /// <summary>
        ///     The default scope for Exchange Online ("https://outlook.office365.com/.default")
        /// </summary>
        public static readonly Scope Outlook365_Default =
            new("https://outlook.office365.com/.default");

        #endregion
    }
}

异常信息（中文翻译） #

Microsoft.Exchange.WebServices.Data.ServiceRequestException: 从服务接收的响应不包含有效的XML。 ---> System.Xml.XmlException: 缺少根元素。
   在 System.Xml.XmlTextReaderImpl.Throw(Exception e)
   在 System.Xml.XmlTextReaderImpl.ParseDocumentContent()
   在 System.Xml.XmlTextReaderImpl.Read()
   在 System.Xml.XmlAsyncCheckReader.Read()
   在 System.Xml.XmlCharCheckingReader.Read()
   在 Microsoft.Exchange.WebServices.Data.EwsXmlReader.Read()
   在 Microsoft.Exchange.WebServices.Data.EwsXmlReader.Read(XmlNodeType nodeType)
   在 Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadXmlDeclaration(EwsServiceXmlReader reader)
   --- 内部异常堆栈跟踪结束 ---
   在 Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadXmlDeclaration(EwsServiceXmlReader reader)
   在 Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadPreamble(EwsServiceXmlReader ewsXmlReader)
   在 Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadResponse(EwsServiceXmlReader ewsXmlReader, WebHeaderCollection responseHeaders)
   在 Microsoft.Exchange.WebServices.Data.SimpleServiceRequestBase.ReadResponseXml(Stream responseStream, WebHeaderCollection responseHeaders)
   在 Microsoft.Exchange.WebServices.Data.SimpleServiceRequestBase.ReadResponse(IEwsHttpWebResponse response)
   在 Microsoft.Exchange.WebServices.Data.SimpleServiceRequestBase.<InternalExecuteAsync>d__1.MoveNext()
--- 之前引发异常的位置的堆栈跟踪结束 ---
   在 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   在 System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   在 Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.<ExecuteAsync>d__6.MoveNext()
--- 之前引发异常的位置的堆栈跟踪结束 ---
   在 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   在 System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   在 Microsoft.Exchange.WebServices.Data.Item.<InternalCreate>d__12.MoveNext()
--- 之前引发异常的位置的堆栈跟踪结束 ---
   在 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   在 System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   在 Microsoft.Exchange.WebServices.Data.EmailMessage.<InternalSend>d__6.MoveNext()
--- 之前引发异常的位置的堆栈跟踪结束 ---
   在 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   在 System.Runtime.CompilerServices.TaskAwaiter.GetResult()

解决方案 #

• 核心错误修正：你把OAuth跳转地址MyEntraAppRedirectUri赋值给了ExchangeService.Url，这是错误的。EWS客户端需要指向Exchange Online的EWS端点，把这一行代码修改为：

  Url = new Uri(Outlook365EndpointUrl),
  

• 优化异步调用：当前GetToken方法用Result同步阻塞获取Token，建议改为异步实现，避免死锁风险：

  private static async Task<AuthenticationResult> GetTokenAsync()
  {
      var applicationBuilder = ConfidentialClientApplicationBuilder
          .Create(MyEntraAppClientId)
          .WithClientSecret(MyClientSecretValue)
          .WithTenantId(MyEntraAppTenantId)
          .Build();
  
      var ewsScopes = new string[] { Scope.Outlook365_Default.Value };
      return await applicationBuilder.AcquireTokenForClient(ewsScopes).ExecuteAsync();
  }
  

  然后在ConnectUsingAppOnlyAuthentication中调用：

  var authResult = await GetTokenAsync();
  

• 权限确认：因为是应用-only模式，确保Entra应用已添加EWS.AccessAsApp应用权限，并且完成了管理员同意操作。

内容的提问来源于stack exchange，提问作者user884248