没有ServiceAccount的Gmail OAUTH 2.0

我试图发送一封具有OAUTH 2.0身份验证的电子邮件,如下所示:

        var certificate = new X509Certificate2(@"C:\path\to\my.p12", "mypassword", X509KeyStorageFlags.Exportable);

        var credential = new ServiceAccountCredential(new ServiceAccountCredential
            .Initializer("my@id.gserviceaccount.com")
        {
            Scopes = new[] { "https://mail.google.com/" },
            User = "scm.beartung@gmail.com"
        }.FromCertificate(certificate));

        bool result = await credential.RequestAccessTokenAsync(CancellationToken.None);


        // send email
        using (var client = new SmtpClient())
        {
            client.Connect("smtp.gmail.com", 587, false);
            client.Authenticate("user.name", credential.Token.AccessToken);
            client.Send(myMessage);
            client.Disconnect(true);
        }

但当我运行这段代码时,我得到了TokenResponseException:“客户端未经授权使用此方法检索访问令牌。” 我需要授权我的客户,这是对的吗?只有G诉讼账户才可能?所以我必须支付一个管理员帐户或者删除OAUTH?