Visual C++ - Send Email using Microsoft OAuth 2.0 (Modern Authentication) + EWS Protocol from Office 365 in Background Service

You can send email using traditional user/password authentication from Office 365 account by EWS Protocol.

However Microsoft will disable traditional user authentication in the future, switching to Microsoft OAuth (Modern Authentication) is strongly recommended now.

Installation

EASendMail is a SMTP component which supports all operations of SMTP/ESMTP protocols (RFC 821, RFC 822, RFC 2554). Before you can use the following example codes, you should download the EASendMail Installer and install it on your machine at first.

Add Reference

To use EASendMail SMTP ActiveX Object in your C++ project, the first step is “Add header files of EASendMail to your project”. Please go to C:\Program Files\EASendMail\Include\tlh or C:\Program Files (x86)\EASendMail\Include\tlh folder, find easendmailobj.tlh and easendmailobj.tli, and then copy these files to your project folder.

add reference in Visual C++

Office 365 OAuth 2.0 client credentials grant

Normal OAuth requires user input user/password for authentication. Obviously, it is not suitable for background service. In this case, You can use the OAuth 2.0 client credentials grant, sometimes called two-legged OAuth, to access web-hosted resources by using the identity of an application. It only works for Office365 user, it doesn’t work for personal Hotmail account.

Create your application in Azure Portal

To use Microsoft/Office365/Live OAuth (Modern Authentication) in your application, you must create a application in https://portal.azure.com.

Important

You can use any Microsoft user to create the application, it doesn’t require application owner is administrator in your Office365 domain. But your Office365 administrator must authorize the application to access user mailbox.

  • Sign in to the Azure portal using either a work or school account or a personal Microsoft account.

  • If your account gives you access to more than one tenant, select your account in the top right corner, and set your portal session to the Azure AD tenant that you want.

  • In the left-hand navigation pane, select the Azure Active Directory service, and then select App registrations -> New registration.

    azure portal new app registration
  • When the Register an application page appears, enter your application’s registration information:

    azure portal app registration information
    • Name - Enter a meaningful application name that will be displayed to users of the app.
    • Supported account types - Select which accounts you would like your application to support. Because we need to support all Office 365 and LIVE SDK (hotmail, outlook personal account) select Accounts "in any organizational directory and personal Microsoft accounts".
  • Redirect URI (optional)

    Select the type of app you’re building, Web or Public client (mobile & desktop), and then enter the redirect URI (or reply URL) for your application.

    For web applications, provide the base URL of your app. For example, http://localhost:31544 might be the URL for a web app running on your local machine. Users would use this URL to sign in to a web client application.

    For public client applications, provide the URI used by Azure AD to return token responses. Enter a value specific to your application, such as myapp://auth.

  • Client Id/secrets

    After you registered your application, Azure AD assigns a unique application (client) ID to your app, and you’re taken to your application’s Overview page. click "Certificates and secrets" -> "client secrets" and add a new client secret.

Important

Please store "client secret" by yourself, because it is hidden when you view it at next time.

API Permission

Click "API Permission" -> "Add a permission" -> "Exchange" -> "Application permissions" -> "Check full_access_as_app" -> "Add a permission" -> "Microsoft Graph" -> "Delegated Permission" -> "User.Read", "email", "offline_access", "openid" and "profile".

azure app api permission

Authentication

  • Click "Authentication"

    • Implicit grant: check "Access tokens" and "ID tokens";
    • Redirect URI: input the url to get authorization code, for native desktop application, you don’t have to add redirect uri.
  • Mobile and desktop applications -> Redirect Uri, please check or add the following URI.

    https://login.microsoftonline.com/common/oauth2/nativeclient
    https://login.live.com/oauth20_desktop.srf
    http://127.0.0.1
    

    Note

    • https://login.live.com/oauth20_desktop.srf is used for Live SDK, http://127.0.0.1 is used for local Http Listener.
  • Supported account types:

    Select Accounts in any organizational directory (Any Azure AD directory - Multitenant) and personal Microsoft accounts (e.g. Skype, Xbox)

  • Advanced settings:

    Set both "Live SDK Support" and "Treat application as a public client" to "Yes".

azure app authentication Overview

Above client id and client secret support both "Office365 + EWS" and "Live (hotmail, outlook personal account) + SMTP", Office365 OAuth doesn’t support SMTP with Application permissions, only EWS is supported.

Visual C++ - Send Email using Microsoft OAuth 2.0 from Office 365 Account in Background Service - Example

#include "stdafx.h" // pre-compile header

#include "C:\Program Files (x86)\EASendMail\Include\tlh\EASendMailObj.tlh"
using namespace EASendMailObjLib;

#include "C:\Program Files (x86)\EASendMail\Include\tlh\msxml3.tlh"
using namespace MSXML2;

const int ConnectNormal = 0;
const int ConnectSSLAuto = 1;
const int ConnectSTARTTLS = 2;
const int ConnectDirectSSL = 3;
const int ConnectTryTLS = 4;

const int AuthAuto = -1;
const int AuthLogin = 0;
const int AuthNtlm = 1;
const int AuthCramMd5 = 2;
const int AuthPlain = 3;
const int AuthMsn = 4;
const int AuthXoauth2 = 5;

BOOL RequestAccessToken(const char* requestData, _bstr_t &accessToken)
{
    try
    {
        IServerXMLHTTPRequestPtr httpRequest = NULL;
        httpRequest.CreateInstance(__uuidof(MSXML2::ServerXMLHTTP));
        if (httpRequest == NULL)
        {
            printf("Failed to create XML HTTP Object, please make sure you install MSXML 3.0 on your machine.\r\n");
            return FALSE;
        }

        _bstr_t fullRequest = requestData;

        const char* postData = (const char*)fullRequest;
        LONG cdata = strlen(postData);
        LPSAFEARRAY psaHunk = ::SafeArrayCreateVectorEx(VT_UI1, 0, cdata, NULL);
        for (LONG k = 0; k < (int)cdata; k++)
        {
            BYTE ch = (BYTE)postData[k];
            ::SafeArrayPutElement(psaHunk, &k, &ch);
        }

        _variant_t requestBuffer;
        requestBuffer.vt = (VT_ARRAY | VT_UI1);
        requestBuffer.parray = psaHunk;

        // If your application is not created by Office365 administrator,
        // please use Office365 directory tenant id, you should ask Offic365 administrator to send it to you.
        // Office365 administrator can query tenant id in https://portal.azure.com/ - Azure Active Directory.
        const char* tenant_id = "79a42c6f-5a9a-439b-a2ca-7aa1b0ed9776";

        _variant_t async(true);
        _bstr_t tokenUri("https://login.microsoftonline.com/");
        tokenUri += _bstr_t(tenant_id);
        tokenUri += _bstr_t("/oauth2/v2.0/token");

        httpRequest->setOption((MSXML2::SERVERXMLHTTP_OPTION)2, 13056);
        httpRequest->open(L"POST", tokenUri, async, vtMissing, vtMissing);
        httpRequest->setRequestHeader(L"Content-Type", L"application/x-www-form-urlencoded");
        httpRequest->send(requestBuffer);

        while (httpRequest->readyState != 4) {
            httpRequest->waitForResponse(1);
        }

        long status = httpRequest->status;
        _bstr_t responseText = httpRequest->responseText;

        if (status < 200 || status >= 300)
        {
            printf("Failed to get access token from server: %d %s\r\n", status, (const char*)responseText);
            return FALSE;
        }

        IOAuthResponseParserPtr oauthParser = NULL;
        oauthParser.CreateInstance(__uuidof(EASendMailObjLib::OAuthResponseParser));
        oauthParser->Load(responseText);

        accessToken = oauthParser->AccessToken;
        if (accessToken.length() == 0)
        {
            printf("Failed to parse access token from server response: %d %s\r\n", status, (const char*)responseText);
            return FALSE;
        }

        return TRUE;
    }
    catch (_com_error &ep)
    {
        printf("Failed to get access token: %s", (const char*)ep.Description());
        return FALSE;
    }
}

_bstr_t GenerateRequestData()
{
    // You should create your client id and client secret,
    // do not use the following client id in production environment, it is used for test purpose only.
    const char* client_id = "8f54719b-4070-41ae-91ad-f48e3c793c5f";
    const char* client_secret = "cbmYyGQjz[d29wL2ArcgoO7HLwJXL/-.";
    const char* scope = "https://outlook.office365.com/.default";

    _bstr_t buffer = "client_id=";
    buffer += client_id;
    buffer += "&client_secret=";
    buffer += client_secret;
    buffer += "&scope=";
    buffer += scope;
    buffer += "&grant_type=client_credentials";

    return buffer;
}

void SendEmail()
{
    ::CoInitialize(NULL);

    _bstr_t accessToken;
    // request access token from MS server without user interaction
    if (!RequestAccessToken((const char*)GenerateRequestData(), accessToken))
    {
        return;
    }

    const char* Office365User = "user@mydomain.onmicrosoft.com";

    IMailPtr oSmtp = NULL;
    oSmtp.CreateInstance(__uuidof(EASendMailObjLib::Mail));
    oSmtp->LicenseCode = _bstr_t("TryIt");

    // Office365 EWS server address
    oSmtp->ServerAddr = _bstr_t("outlook.office365.com");

    // Set Exchange Web Service Protocol - EWS - Exchange 2007/2010/2013/2016/2019/Office365
    oSmtp->Protocol = 1;

    // Enable SSL/TLS connection
    oSmtp->ConnectType = ConnectSSLAuto;

    // OAUTH/XOAUTH2 type
    oSmtp->AuthType = AuthXoauth2;
    oSmtp->UserName = _bstr_t(Office365User);
    oSmtp->Password = accessToken;

    oSmtp->FromAddr = _bstr_t(Office365User);

    // Please change recipient address to yours for test
    oSmtp->AddRecipient(_bstr_t("Support Team"),
        _bstr_t("support@emailarchitect.net"), 0);

    oSmtp->Subject = _bstr_t("Test email from Office 365 using EWS OAUTH");
    oSmtp->BodyText = _bstr_t("Hello, this is a test....");

    if (oSmtp->SendMail() == 0)
        printf("Message delivered!");
    else
        printf((const char*)oSmtp->GetLastErrDescription());
}

TLS 1.2 Protocol

TLS is the successor of SSL, more and more SMTP servers require TLS 1.2 encryption now.

If your operating system is Windows XP/Vista/Windows 7/Windows 2003/2008/2008 R2/2012/2012 R2, you need to enable TLS 1.2 protocol in your operating system like this:

Enable TLS 1.2 on Windows XP/Vista/7/10/Windows 2008/2008 R2/2012

Appendix

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