Smtp OAuth 2.0

using MailKit.Net.Smtp;
using MailKit.Security;
using MailKit;
using MimeKit;
using Microsoft.Identity.Client;
using System.Net.Http.Headers;
using System.ComponentModel.DataAnnotations;
[HttpPost("{dbname}/{credtype}")]
        public async Task<ActionResult> SendEmailAuth2(string dbname, ReceiverEmail _ReceiverEmail, string credtype)
        {
            // <PackageReference Include="MailKit" Version="4.12.0" />
            // <PackageReference Include="Microsoft.Identity.Client" Version="4.71.1" />

            var companydata = await _IUtilityMethodsRepository.GetCompanyMstInfo(dbname);
            var senderinfo = await _IEmailRepository.GetSenderEmailCredentials(dbname);
            if (credtype == "S")
            {
                senderinfo = await _IEmailRepository.GetSenderEmailCredentials("erpcrew");
            }

            _ReceiverEmail.msgcode = 2;

            if (senderinfo != null)
            {
                // Get OAuth token
                var clientId = "2cbc367c-ed76-4b58-b346-e460abc49b38";
                var tenantId = "7fc68e96-5940-4ae4-a62b-d3f42afbb1e5";
                var clientSecret = "rPX8Q~heG8qhlpInG~KwNFzNN2f2i9wpTvhDgbRs";

                var confidentialClient = ConfidentialClientApplicationBuilder.Create(clientId)
                    .WithClientSecret(clientSecret)
                    .WithAuthority($"https://login.microsoftonline.com/{tenantId}")
                    .Build();

                var result = await confidentialClient.AcquireTokenForClient(new[] {
                    "https://outlook.office365.com/.default"
                }).ExecuteAsync();

                var accessToken = result.AccessToken;
                using var smtp = new MailKit.Net.Smtp.SmtpClient();
                await smtp.ConnectAsync("smtp.office365.com", 587, SecureSocketOptions.StartTls);
                var oauth2 = new SaslMechanismOAuth2(senderinfo.username, accessToken);

                var MailInfo = new MimeMessage();
                MailInfo.From.Add(new MailboxAddress(companydata.CompanyName, senderinfo.mailfrom));

                if (!string.IsNullOrEmpty(_ReceiverEmail.email1))
                {
                    MailInfo.To.Add(MailboxAddress.Parse(_ReceiverEmail.email1));
                }
                if (!string.IsNullOrEmpty(_ReceiverEmail.email2))
                {
                    MailInfo.To.Add(MailboxAddress.Parse(_ReceiverEmail.email2));
                }
                if (!string.IsNullOrEmpty(_ReceiverEmail.email3))
                {
                    MailInfo.To.Add(MailboxAddress.Parse(_ReceiverEmail.email3));
                }
                if (!string.IsNullOrEmpty(_ReceiverEmail.email4))
                {
                    foreach (string multiemail in _ReceiverEmail.email4.Split(';'))
                    {
                        if (multiemail.Length > 0)
                        {
                            MailInfo.To.Add(MailboxAddress.Parse(multiemail.Replace("\r\n", "")));
                        }
                    }
                }

                MailInfo.Subject = _ReceiverEmail.emailsubject;
                var builder = new BodyBuilder { HtmlBody = _ReceiverEmail.emailmessage };

                string pathname = "";
                if (!string.IsNullOrEmpty(_ReceiverEmail.emailfilename))
                {
                    pathname = "\\MFGReports\\Reports\\" + dbname + "\\" + _ReceiverEmail.emailfilename;
                    if(credtype == "S")
                    {
                        pathname = "\\MFGReports\\Docs\\" + dbname + "\\" + _ReceiverEmail.subfoldername + "\\" + _ReceiverEmail.emailfilename;
                    }

                    var pathfilename = Path.GetFullPath(pathname);
                    builder.Attachments.Add(pathfilename);
                }

                MailInfo.Body = builder.ToMessageBody();

               
                await smtp.AuthenticateAsync(oauth2);
                await smtp.SendAsync(MailInfo);
                await smtp.DisconnectAsync(true);

                if (!string.IsNullOrEmpty(pathname))
                    System.IO.File.Delete(pathname);

                _ReceiverEmail.msgcode = 1;
            }

            return Ok(_ReceiverEmail);
        }

        [HttpPost("{dbname}/{credtype}")]
        public async Task<ActionResult> SendEmailAuth2GraphApi(string dbname, ReceiverEmail _ReceiverEmail, string credtype)
        {
            var companydata = await _IUtilityMethodsRepository.GetCompanyMstInfo(dbname);
            var senderinfo = await _IEmailRepository.GetSenderEmailCredentials(dbname);
            if (credtype == "S")
            {
                senderinfo = await _IEmailRepository.GetSenderEmailCredentials("erpcrew");
            }

            _ReceiverEmail.msgcode = 2;

            if (senderinfo != null)
            {
                // Get OAuth token
                var clientId = "2cbc367c-ed76-4b58-b346-e460abc49b38";
                var tenantId = "7fc68e96-5940-4ae4-a62b-d3f42afbb1e5";
                var clientSecret = "rPX8Q~heG8qhlpInG~KwNFzNN2f2i9wpTvhDgbRs";

                var confidentialClient = ConfidentialClientApplicationBuilder.Create(clientId)
                    .WithClientSecret(clientSecret)
                    .WithAuthority($"https://login.microsoftonline.com/{tenantId}")
                    .Build();

                var result = await confidentialClient.AcquireTokenForClient([
                    "https://graph.microsoft.com/.default"
                ]).ExecuteAsync();
                

                var accessToken = result.AccessToken;

                // Prepare email message
                var emailMessage = new
                {
                    message = new
                    {
                        subject = _ReceiverEmail.emailsubject,
                        body = new { contentType = "HTML", content = _ReceiverEmail.emailmessage },
                        toRecipients = new List<object>(),
                        attachments = new List<object>(),
                        from = new {
                            emailAddress = new {
                                name = companydata.CompanyName,   // Display name shown to the recipient
                                address = senderinfo.mailfrom     // Actual email address used to send
                            }
                        }
                    },
                    saveToSentItems = true
                };
                 _ReceiverEmail.email1 = "udit@erpcrystal.in";
                 _ReceiverEmail.email2 = "udit@erpcrystal.in";
                 _ReceiverEmail.email3 = "udit@erpcrystal.in";
                // **Handle Multiple Recipients**
                foreach (var email in new[] { _ReceiverEmail.email1, _ReceiverEmail.email2, _ReceiverEmail.email3 })
                {
                    if (!string.IsNullOrEmpty(email))
                    {
                        emailMessage.message.toRecipients.Add(new { emailAddress = new { address = email } });
                    }
                }

                if (!string.IsNullOrEmpty(_ReceiverEmail.email4))
                {
                    foreach (string multiemail in _ReceiverEmail.email4.Split(';'))
                    {
                        if (!string.IsNullOrEmpty(multiemail))
                        {
                            emailMessage.message.toRecipients.Add(new { emailAddress = new { address = multiemail.Trim() } });
                        }
                    }
                }

                // **Handle Attachments**
                string pathname = "";
                if (!string.IsNullOrEmpty(_ReceiverEmail.emailfilename))
                {
                    pathname = $"\\MFGReports\\Reports\\{dbname}\\{_ReceiverEmail.emailfilename}";
                    if (credtype == "S")
                    {
                        pathname = $"\\MFGReports\\Docs\\{dbname}\\{_ReceiverEmail.subfoldername}\\{_ReceiverEmail.emailfilename}";
                    }

                    var fileBytes = System.IO.File.ReadAllBytes(Path.GetFullPath(pathname));
                    var base64File = Convert.ToBase64String(fileBytes);

                    emailMessage.message.attachments.Add(new
                    {
                        name = _ReceiverEmail.emailfilename,
                        contentBytes = base64File,
                        contentType = "application/octet-stream"
                    });

                    
                }

                // **Send Email via Graph API**
                var httpClient = new HttpClient();
                httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
                // var IsValid = await httpClient.GetFromJsonAsync<dynamic>(@$"https://graph.microsoft.com/v1.0/users/udit@erpcrystal.in");
                var response = await httpClient.PostAsJsonAsync(@$"https://graph.microsoft.com/v1.0/users/{_ReceiverEmail.email1}/sendMail", emailMessage);

                if (!response.IsSuccessStatusCode)
                {
                    Console.WriteLine($"Error sending email: {response.StatusCode}");
                    return BadRequest("Failed to send email.");
                }
                // Delete file after sending
                    System.IO.File.Delete(pathname);
                _ReceiverEmail.msgcode = 1;
            }

            return Ok(_ReceiverEmail);
        }

    <PackageReference Include="MailKit" Version="4.12.0" />
    <PackageReference Include="Microsoft.Identity.Client" Version="4.71.1" />
    <PackageReference Include="Microsoft.Graph" Version="5.77.0" />