Visual C++ - Send email using Google/Gmail OAuth 2.0 authentication¶

#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;

void SendMailWithXOAUTH2(const char* lpszEmail, const char* lpszAccessToken)
{
    IMailPtr oSmtp = NULL;
    oSmtp.CreateInstance(__uuidof(EASendMailObjLib::Mail));
    oSmtp->LicenseCode = _bstr_t("TryIt");

    // Gmail SMTP server address
    oSmtp->ServerAddr = _bstr_t("smtp.gmail.com");
    // Using 587 port, you can also use 465 or 25 port
    oSmtp->ServerPort = 587;

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

    //  XOAUTH 2.0 authentication
    oSmtp->AuthType = AuthXoauth2;
    // set user authentication
    oSmtp->UserName = lpszEmail;
    // use access token as password
    oSmtp->Password = lpszAccessToken;

    // Your email address
    oSmtp->FromAddr = lpszEmail;
    // 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 gmail account using OAUTH 2");
    oSmtp->BodyText = _bstr_t("Hello, this is a test email ....");

    printf("start to send email using OAUTH 2.0 ...\n");

    if (oSmtp->SendMail() == 0)
        printf("The email has been submitted to server successfully!\n");
    else
        printf("%s\n", (const char*)oSmtp->GetLastErrDescription());
}


// 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 = "507778793027-cfod2rvnnks95ed17d7ejepp16l1tvg8.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/auth";
const char* tokenUri = "https://oauth2.googleapis.com/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 DoOauthAndSendEmail()
{
    IHttpListenerPtr httpListener = NULL;
    httpListener.CreateInstance(__uuidof(EASendMailObjLib::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(EASendMailObjLib::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(EASendMailObjLib::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);

    SendMailWithXOAUTH2((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();

    DoOauthAndSendEmail();

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

    return 0;
}