无法通过具有授权权限的Microsoft Graph API发送电子邮件

我创建了一个C＃控制台应用程序，以使用Microsoft Graph API发送电子邮件。添加Mail.Send应用程序权限后，它可以正常工作。但是，由于公司的要求，我被要求改用Mail.Send Delegated Permission，但在该权限下，我认为它没有用，并且出现此错误：

添加Mail.Send Delegated Permission后，我应该考虑采取任何措施以使其正常工作吗？

这是我的代码：

    static void Main(string[] args)
    {
        // Azure AD APP
        string clientId = "<client Key Here>";
        string tenantID = "<tenant key here>";
        string clientSecret = "<client secret here>";

        Task<GraphServiceClient> callTask = Task.Run(() => SendEmail(clientId, tenantID, clientSecret));
        // Wait for it to finish
        callTask.Wait();
        // Get the result
        var astr = callTask;
    }

    public static async Task<GraphServiceClient> SendEmail(string clientId, string tenantID, string clientSecret)
    {

        var confidentialClientApplication = ConfidentialClientApplicationBuilder
            .Create(clientId)
            .WithTenantId(tenantID)
            .WithClientSecret(clientSecret)
            .Build();

        var authProvider = new ClientCredentialProvider(confidentialClientApplication);       

        var graphClient = new GraphServiceClient(authProvider);

        var message = new Message
            {
                Subject = subject,
                Body = new ItemBody
                {
                    ContentType = BodyType.Text,
                    Content = content
                },
                ToRecipients = new List<Recipient>()
                {
                    new Recipient
                    {
                        EmailAddress = new EmailAddress { Address = recipientAddress }
                    }
                }
            };

         var saveToSentItems = true;

         await _graphClient.Users[<userprincipalname>]
                                .SendMail(message, saveToSentItems)
                                .Request()
                                .PostAsync();

        return graphClient;

    }

更新：

根据以下答案，我将代码更新如下：

var publicClientApplication = PublicClientApplicationBuilder
            .Create("<client-id>")
            .WithTenantId("<tenant-id>")
            .Build();

            var authProvider = new UsernamePasswordProvider(publicClientApplication);

var secureString = new NetworkCredential("", "<password>").SecurePassword;

User me = await graphClient.Me.Request()
                .WithUsernamePassword("<username>", secureString)
                .GetAsync();

我启用了“允许公共客户端流”来修复异常。

现在，我看到另一个异常：没有足够的权限来完成操作。

我想念什么？