Visual C++ - Retrieve email using Microsoft OAuth 2.0 (Modern Authentication) + EWS protocol from Office 365 in background service

You can retrieve email using traditional user/password authentication from Office 365 account by EWS Protocol. IMAP4 protocol is not supported in background service.

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

Installation

Before you can use the following sample codes, you should download the EAGetMail Installer and install it on your machine at first. Full sample projects are included in this installer.

Add reference

To better demonstrate how to retrieve email and parse email, let’s create a Visual C++ console project named “receiveemail” at first, and then add the reference of EAGetMail in your project.

Visual C++ console project

To use EAGetMail POP3 & IMAP4 ActiveX Object in your project, the first step is “Add header files of EAGetMail to your project”. Please go to C:\Program Files\EAGetMail\Include\tlh or C:\Program Files (x86)\EAGetMail\Include\tlh folder, find eagetmailobj.tlh and eagetmailobj.tli, and then copy these files to your project folder. You can start to use it to retrieve email and parse email in your project.

add reference in 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 Azure Portal.

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

Single tenant and multitenant in account type

When the register an application page appears, enter a meaningful application name and select the account type.

Select which accounts you would like your application to support.

  • If your application only supports the users in your directory or organization, please select Single tenant type;
  • If your application needs to support all users in Office 365 and Microsoft personal account (hotmail.com, outlook.com), please select Multitenant type, and you must verify publisher.

Because we just need to support Offic365 user in our organization, so select Accounts in this organizational directory only (single tenant).

Do not select supporting Microsoft personal account, because there is no way to access Microsoft personal account in background service.

Important

If you don’t verify publisher for multitenant application, your application will not request access token successfully.

API permissions

  • Click API Permission -> Microsoft Graph -> Delegated Permission -> User.Read.
  • Click API Permission -> Add a permission -> APIs in my organization uses -> Office 365 Exchange Online -> Application Permission -> Other permission -> full_access_as_app
azure APIs in my organization uses

Here is permissions list:

azure application api permission list

If your current user is not a user in a verified domain or Offic 365, you will not find Office 365 Exchange Online in API list, then you have to add this API permission manually.

  • Select Manifest in the left-hand navigation under Manage.
  • Locate the requiredResourceAccess property in the manifest, and add the following inside the square brackets ([]):
{
  "resourceAppId": "00000002-0000-0ff1-ce00-000000000000",
  "resourceAccess": [
      {
          "id": "dc890d15-9560-4a4c-9b7f-a736ec74ec40",
          "type": "Role"
      }
  ]
}
  • Select Save.
  • Select API permissions under Manage. Confirm that the full_access_as_app permission is listed.

Client Id and client secrets

Now we need to create a client secret for the application, click Certificates and secrets -> client secrets and add a new client secret.

azure application api permission

After client secret is created, store the client secret value to somewhere.

Important

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

Branding and verify publisher

Now we click Branding, you can edit your company logo, URL and application name. If your application supports multitenant (access user in all Office 365 and Microsoft personal account), you must complete the publisher verification.

It is not difficult, you can have a look at publisher verification. After publisher verification is completed, your branding is like this:

azure application Authentication Overview

Important

You must complete the publisher verification for multitenant application, otherwise, your application will not request access token correctly.

Client id and tenant

Now you can click Overview to find your client id and tenant.

azure application client id and tenant

Access token expiration

You don’t have to request access token every time. By default, access token expiration time is 3600 seconds, you can use the access token repeatedly before it is expired.

Important

You should create your client id and client secret, do not use the client id from example codes in production environment, it is used for test purpose. If you got "This app isn't verified" information, please click "Advanced" -> Go to ... for test.

Visual C++ - Retrieve email using Microsoft OAuth 2.0 from Office 365 account in background service - example

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

#include <stdio.h>
#include <tchar.h>

#include "C:\Program Files (x86)\EAGetMail\Include\tlh\EAGetMailObj.tlh"
using namespace EAGetMailObjLib;

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

const int MailServerPop3 = 0;
const int MailServerImap4 = 1;
const int MailServerEWS = 2;
const int MailServerDAV = 3;

const int MailServerAuthLogin = 0;
const int MailServerAuthCRAM5 = 1;
const int MailServerAuthNTLM = 2;
const int MailServerAuthXOAUTH2 = 3;

const int GetMailInfos_All = 1;
const int GetMailInfos_NewOnly = 2;
const int GetMailInfos_ReadOnly = 4;
const int GetMailInfos_SeqRange = 8;
const int GetMailInfos_UIDRange = 16;
const int GetMailInfos_PR_ENTRYID = 32;
const int GetMailInfos_DateRange = 64;
const int GetMailInfos_OrderByDateTime = 128;

DWORD  _getCurrentPath(LPTSTR lpPath, DWORD nSize)
{
    DWORD dwSize = ::GetModuleFileName(NULL, lpPath, nSize);
    if (dwSize == 0 || dwSize == nSize)
    {
        return 0;
    }

    // Change file name to current full path
    LPCTSTR psz = _tcsrchr(lpPath, _T('\\'));
    if (psz != NULL)
    {
        lpPath[psz - lpPath] = _T('\0');
        return _tcslen(lpPath);
    }

    return 0;
}

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(EAGetMailObjLib::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 RetrieveEmail()
{
    ::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";

    try
    {
        TCHAR szPath[MAX_PATH + 1];
        _getCurrentPath(szPath, MAX_PATH);

        TCHAR szMailBox[MAX_PATH + 1];
        wsprintf(szMailBox, _T("%s\\inbox"), szPath);

        // Create a folder to store emails
        ::CreateDirectory(szMailBox, NULL);

        IMailServerPtr oServer = NULL;
        oServer.CreateInstance(__uuidof(EAGetMailObjLib::MailServer));

        // Office365 server address
        oServer->Server = _bstr_t("outlook.office365.com");
        oServer->User = _bstr_t(Office365User);

        // Use access token as password
        oServer->Password = accessToken;
        // Use OAUTH 2.0
        oServer->AuthType = MailServerAuthXOAUTH2;
        // Use EWS Protocol
        oServer->Protocol = MailServerEWS;

        // Enable SSL Connection
        oServer->SSLConnection = VARIANT_TRUE;

        IMailClientPtr oClient = NULL;
        oClient.CreateInstance(__uuidof(EAGetMailObjLib::MailClient));
        oClient->LicenseCode = _T("TryIt");

        _tprintf(_T("Connecting %s ...\r\n"), (const TCHAR*)oServer->Server);
        oClient->Connect(oServer);

        // Get new email only, if you want to get all emails, please remove this line
        oClient->GetMailInfosParam->GetMailInfosOptions = GetMailInfos_NewOnly;

        IMailInfoCollectionPtr infos = oClient->GetMailInfoList();
        _tprintf(_T("Total %d emails\r\n"), infos->Count);

        for (long i = 0; i < infos->Count; i++)
        {
            IMailInfoPtr pInfo = infos->GetItem(i);

            _tprintf(_T("Index: %d; Size: %d; UIDL: %s\r\n\r\n"),
                pInfo->Index, pInfo->Size, (const TCHAR*)pInfo->UIDL);

            TCHAR szFile[MAX_PATH + 1];
            // Generate a random file name by current local datetime,
            // You can use your method to generate the filename if you do not like it
            SYSTEMTIME curtm;
            ::GetLocalTime(&curtm);
            ::wsprintf(szFile, _T("%s\\%04d%02d%02d%02d%02d%02d%03d%d.eml"),
                szMailBox,
                curtm.wYear,
                curtm.wMonth,
                curtm.wDay,
                curtm.wHour,
                curtm.wMinute,
                curtm.wSecond,
                curtm.wMilliseconds,
                i);

            // Receive email from POP3 server
            IMailPtr oMail = oClient->GetMail(pInfo);

            _tprintf(_T("From: %s\r\n"), (const TCHAR*)oMail->From->Address);
            _tprintf(_T("Subject: %s\r\n"), (const TCHAR*)oMail->Subject);

            // Save email to local disk
            oMail->SaveAs(szFile, VARIANT_TRUE);

            // Mark email as read to prevent retrieving this email again.
            oClient->MarkAsRead(pInfo, VARIANT_TRUE);

            // If you want to delete current email, please use Delete method instead of MarkAsRead
            // oClient->Delete(pInfo);
        }

        // Delete method just mark the email as deleted,
        // Quit method expunge the emails from server exactly.
        oClient->Quit();
    }
    catch (_com_error &ep)
    {
        _tprintf(_T("Error: %s\r\n"), (const TCHAR*)ep.Description());
    }

}

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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