Microsoft Graph调用报错：Content type text/html无注册解析工厂

我正在按照微软官方的Outlook邮件控制台应用教程操作，严格遵循步骤执行，但在发送GET请求获取收件箱邮件时，遇到如下异常：

Content type text/html does not have a factory registered to be parsed.

我尝试添加清除请求头并设置Accept为application/json的代码修复问题，但仍未解决，相关代码如下：

public static Task<MessageCollectionResponse?> GetInboxAsync(){
    // Ensure client isn't null
    _ = _userClient ??
        throw new System.NullReferenceException("Graph has not been initialized for user auth");

    return _userClient.Me
        // Only messages from Inbox folder
        .MailFolders["Inbox"]
        .Messages
        .GetAsync((config) =>
        {
            //The next two lines were added by me to try to fix the problem
            config.Headers.Clear();
            config.Headers.Add("Accept", "application/json");
            // Only request specific properties
            config.QueryParameters.Select = new[] { "from", "isRead", "receivedDateTime", "subject" };
            // Get at most 25 results
            config.QueryParameters.Top = 25;
            // Sort by received time, newest first
            config.QueryParameters.Orderby = new[] { "receivedDateTime DESC" };
        });
}

这个错误本质是Graph API返回了HTML格式的内容（通常是错误页面），而非预期的JSON响应，核心问题不在Accept头设置，而是请求本身无效。可以按以下步骤排查修复：

1. 删除手动操作请求头的代码
   config.Headers.Clear()会清空Graph SDK自动添加的关键请求头（比如身份验证令牌Authorization），直接导致请求无效，API返回错误页面。删掉这两行手动设置的代码，SDK会自动处理正确的请求头：

   public static Task<MessageCollectionResponse?> GetInboxAsync(){
       // Ensure client isn't null
       _ = _userClient ??
           throw new System.NullReferenceException("Graph has not been initialized for user auth");
   
       return _userClient.Me
           .MailFolders["Inbox"]
           .Messages
           .GetAsync((config) =>
           {
               config.QueryParameters.Select = new[] { "from", "isRead", "receivedDateTime", "subject" };
               config.QueryParameters.Top = 25;
               config.QueryParameters.Orderby = new[] { "receivedDateTime DESC" };
           });
   }
   

2. 检查用户客户端初始化配置
   确认_userClient初始化时，是否正确配置了Mail.Read权限范围，且身份验证流程成功获取到了有效令牌。权限不足或认证失败时，API会返回HTML格式的错误提示。

3. 捕获并查看实际响应内容
   添加异常捕获逻辑，直接查看API返回的HTML内容，定位具体错误原因：

   try
   {
       var response = await GetInboxAsync();
   }
   catch (ODataErrorException ex)
   {
       Console.WriteLine($"错误信息: {ex.Message}");
       Console.WriteLine($"响应内容: {ex.Response.Content}");
   }
   catch (HttpRequestException ex)
   {
       Console.WriteLine($"请求错误: {ex.Message}");
   }
   

4. 确认应用注册权限
   登录Azure门户，检查对应应用注册是否已添加Mail.Read委托权限，且已完成管理员同意（如果是面向租户的应用）。

内容的提问来源于stack exchange，提问作者Khaled Ayman