Visual C++ - Retrieve email using Google/Gmail OAuth 2.0 authentication + IMAP protocol¶

#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 MailServerMsGraph = 4;

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;
}

void RetrieveWithXOAUTH2(const char* lpszEmail, const char* lpszAccessToken)
{
    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));

        // Gmail IMAP server address
        oServer->Server = _bstr_t("imap.gmail.com");
        oServer->User = _bstr_t(lpszEmail);

        // Use access token as password
        oServer->Password = _bstr_t(lpszAccessToken);
        // Use OAUTH 2.0
        oServer->AuthType = MailServerAuthXOAUTH2;
        // Use IMAP4 Protocol
        oServer->Protocol = MailServerImap4;

        // Enable SSL Connection
        oServer->SSLConnection = VARIANT_TRUE;
        // Set IMAP4 SSL Port
        oServer->Port = 993;

        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"), (const TCHAR*)ep.Description());
    }
}

// client configuration
// 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* clientID = "570831866161-ha6qpdnke22f7mhf0d50ui22f427drjt.apps.googleusercontent.com";
const char* clientSecret = "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";
const char* scope = "openid%20profile%20email%20https://mail.google.com";
const char* authUri = "https://accounts.google.com/o/oauth2/v2/auth";
const char* tokenUri = "https://www.googleapis.com/oauth2/v4/token";

// path?parameter1=value1&parameter2=value2#anchor;
_bstr_t ParseParameter(const char* uri, const char* key)
{
    _bstr_t value = "";
    if (uri == NULL || key == NULL)
        return value;

    const char* p = strchr(uri, '?');
    p = (p != NULL) ? p + 1 : uri;

    do
    {
        if (_strnicmp(p, key, strlen(key)) == 0)
        {
            p += strlen(key);
            const char* pend = strpbrk(p, "&#");
            if (pend != NULL)
            {
                char* buf = new char[pend - p + 1];
                memcpy(buf, p, pend - p);
                buf[pend - p] = '\0';
                value = buf;

                delete[] buf;
            }
            else
            {
                value = p;
            }

            return value;
        }

        p = strchr(p, '&');
        if (p) p++;

    } while (p);

    return value;
}

_bstr_t RequestAccessToken(const char* code, const char* redirectUri)
{
    printf("Exchanging code for tokens...\n");

    _bstr_t responseText = "";
    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.\n");
            return responseText;
        }

        _bstr_t tokenRequestBody = "code=";
        tokenRequestBody += code;
        tokenRequestBody += "&redirect_uri=";
        tokenRequestBody += redirectUri;
        tokenRequestBody += "&client_id=";
        tokenRequestBody += clientID;
        tokenRequestBody += "&client_secret=";
        tokenRequestBody += clientSecret;
        tokenRequestBody += "&grant_type=authorization_code";

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

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

        _variant_t async(true);

        httpRequest->setOption((MSXML2::SERVERXMLHTTP_OPTION)2, 13056);
        httpRequest->open(L"POST", _bstr_t(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;
        responseText = httpRequest->responseText;

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

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

    return responseText;
}

void DoOauthAndRetrieveEmail()
{
    IHttpListenerPtr httpListener = NULL;
    httpListener.CreateInstance(__uuidof(EAGetMailObjLib::HttpListener));

    // Creates a redirect URI using an available port on the loopback address.
    if (httpListener->Create("127.0.0.1", 0) == VARIANT_FALSE)
    {
        printf("Failed to listen on %s\n", (const char*)httpListener->GetLastError());
        return;
    }

    char szUri[MAX_PATH + 1];
    sprintf_s(szUri, MAX_PATH, "http://127.0.0.1:%d", httpListener->ListenPort);
    printf("listen on %s ...\n", szUri);

    // Creates the OAuth 2.0 authorization request.
    _bstr_t authorizationRequest = authUri;
    authorizationRequest += "?response_type=code&scope=";
    authorizationRequest += scope;
    authorizationRequest += "&redirect_uri=";
    authorizationRequest += szUri;
    authorizationRequest += "&client_id=";
    authorizationRequest += clientID;

    printf("open %s ...\n", (const char*)authorizationRequest);

    // Opens request in the browser.
    IBrowserUiPtr browserUi = NULL;
    browserUi.CreateInstance(__uuidof(EAGetMailObjLib::BrowserUi));
    browserUi->OpenUrl(authorizationRequest);

    // Waits for the OAuth authorization response.
    if (httpListener->GetRequestUrl(-1) == VARIANT_FALSE)
    {
        printf("Failed to get authorization response %s\n", (const char*)httpListener->GetLastError());
        return;
    }

    // Brings the Console to Focus.
    SetForegroundWindow(GetConsoleWindow());

    // Send response and stop http listener.
    httpListener->SendResponse(_bstr_t("200"),
        _bstr_t("text/html; charset=utf-8"),
        "<html><head></head><body>Please return to the app and close current window.</body></html>");
    httpListener->Close();

    _bstr_t requestUri = httpListener->RequestUrl;
    printf("RequestUri: %s\n", (const char*)requestUri);

    // Checks for errors.
    _bstr_t error = ParseParameter((const char*)requestUri, "error=");
    if (error.length())
    {
        printf("OAuth authorization error: %s\n", (const char*)error);
        return;
    }

    // Check authorization code
    _bstr_t code = ParseParameter((const char*)requestUri, "code=");
    if (code.length() == 0)
    {
        printf("Malformed authorization response: %s\n", (const char*)requestUri);
        return;
    }

    printf("\nAuthorization code: %s\n", (const char*)code);

    _bstr_t responseText = RequestAccessToken((const char*)code, szUri);
    printf("%s\n", (const char*)responseText);

    IOAuthResponseParserPtr parser = NULL;
    parser.CreateInstance(__uuidof(EAGetMailObjLib::OAuthResponseParser));
    parser->Load(responseText);

    _bstr_t user = parser->EmailInIdToken;
    _bstr_t accessToken = parser->AccessToken;

    if (accessToken.length() == 0)
    {
        printf("Failed to request access token, return!\n");
        return;
    }

    printf("User: %s\n", (const char*)user);
    printf("AccessToken: %s\n", (const char*)accessToken);

    RetrieveWithXOAUTH2((const char*)user, (const char*)accessToken);
}

int main()
{
    ::CoInitialize(NULL);

    printf(
        "+------------------------------------------------------------------+\n"
        "  Sign in with Google                                             \n"
        "   If you got \"This app isn't verified\" information in Web Browser, \n"
        "   click \"Advanced\" -> Go to ... to continue test.\n"
        "+------------------------------------------------------------------+\n\n");

    printf("Press ENTER key to sign in...\n");
    getchar();

    DoOauthAndRetrieveEmail();

    printf("Press ENTER key to quit...\n");
    getchar();

    return 0;
}