(C) OAuth2 for a GMail using a P12 Service Account Key

See more GMail REST API Examples

Note: This example does not work for Personal Google Accounts where the email domain is @gmail.com

For more information, see https://www.chilkatsoft.com/google_workspace_setup_smtp_gmail.asp

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#include <C_CkHttp.h>
#include <C_CkCert.h>
#include <C_CkMailMan.h>
#include <C_CkEmail.h>

void ChilkatSample(void)
    {
    HCkHttp http;
    HCkCert cert;
    BOOL success;
    const char *iss;
    const char *scope;
    const char *oauth_sub;
    int numSec;
    const char *accessToken;
    HCkMailMan mailman;
    HCkEmail email;

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    http = CkHttp_Create();

    // --------------------------------------------------------------------------------
    // For a step-by-step guide for setting up your Google Workspace service account,
    // see Setup Google Workspace Account for Sending SMTP GMail from a Service Account
    // --------------------------------------------------------------------------------
    // Begin by loading your Google service account key (.p12)
    cert = CkCert_Create();
    success = CkCert_LoadPfxFile(cert,"c:/someDirectory/keys/chilkat25-cbd7b42afbd8.p12","notasecret");
    if (success != TRUE) {
        printf("%s\n",CkCert_lastErrorText(cert));
        CkHttp_Dispose(http);
        CkCert_Dispose(cert);
        return;
    }

    // The ISS is your service account email address ending in gserviceaccount.com.
    iss = "chilkatsvc@chilkat25.iam.gserviceaccount.com";

    // The scope is always the following string:
    scope = "https://mail.google.com/";

    // The sub is your company email address
    oauth_sub = "bob@yourcompany.com";

    // The access token is valid for this number of seconds.
    numSec = 3600;

    accessToken = CkHttp_g_SvcOauthAccessToken(http,iss,scope,oauth_sub,numSec,cert);
    if (CkHttp_getLastMethodSuccess(http) != TRUE) {
        printf("%s\n",CkHttp_lastErrorText(http));
        CkHttp_Dispose(http);
        CkCert_Dispose(cert);
        return;
    }
    else {
        printf("access token: %s\n",accessToken);
    }

    // The access token allows us to send unlimited emails while it's valid. Once it expires, we must obtain and use a new one.

    // -----------------------------------------------------------------------
    mailman = CkMailMan_Create();

    // Set the properties for the GMail SMTP server:
    CkMailMan_putSmtpHost(mailman,"smtp.gmail.com");
    CkMailMan_putSmtpPort(mailman,587);
    CkMailMan_putStartTLS(mailman,TRUE);

    CkMailMan_putSmtpUsername(mailman,"bob@yourcompany.com");
    CkMailMan_putOAuth2AccessToken(mailman,accessToken);

    // Create a new email object
    email = CkEmail_Create();

    CkEmail_putSubject(email,"This is a test");
    CkEmail_putBody(email,"This is a test");
    CkEmail_putFrom(email,"Bob <bob@yourcompany.com>");
    success = CkEmail_AddTo(email,"Recipient","recipient@example.com");
    // To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

    success = CkMailMan_SendEmail(mailman,email);
    if (success != TRUE) {
        printf("%s\n",CkMailMan_lastErrorText(mailman));
        CkHttp_Dispose(http);
        CkCert_Dispose(cert);
        CkMailMan_Dispose(mailman);
        CkEmail_Dispose(email);
        return;
    }

    success = CkMailMan_CloseSmtpConnection(mailman);
    if (success != TRUE) {
        printf("Connection to SMTP server not closed cleanly.\n");
    }

    printf("Successfully sent email using Gmail with a service account key.\n");


    CkHttp_Dispose(http);
    CkCert_Dispose(cert);
    CkMailMan_Dispose(mailman);
    CkEmail_Dispose(email);

    }