(Java) 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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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkHttp http = new CkHttp();

    // --------------------------------------------------------------------------------
    // 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)
    CkCert cert = new CkCert();
    boolean success = cert.LoadPfxFile("c:/someDirectory/keys/chilkat25-cbd7b42afbd8.p12","notasecret");
    if (success != true) {
        System.out.println(cert.lastErrorText());
        return;
        }

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

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

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

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

    String accessToken = http.g_SvcOauthAccessToken(iss,scope,oauth_sub,numSec,cert);
    if (http.get_LastMethodSuccess() != true) {
        System.out.println(http.lastErrorText());
        return;
        }
    else {
        System.out.println("access token: " + 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.

    // -----------------------------------------------------------------------
    CkMailMan mailman = new CkMailMan();

    // Set the properties for the GMail SMTP server:
    mailman.put_SmtpHost("smtp.gmail.com");
    mailman.put_SmtpPort(587);
    mailman.put_StartTLS(true);

    mailman.put_SmtpUsername("bob@yourcompany.com");
    mailman.put_OAuth2AccessToken(accessToken);

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

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

    success = mailman.SendEmail(email);
    if (success != true) {
        System.out.println(mailman.lastErrorText());
        return;
        }

    success = mailman.CloseSmtpConnection();
    if (success != true) {
        System.out.println("Connection to SMTP server not closed cleanly.");
        }

    System.out.println("Successfully sent email using Gmail with a service account key.");
  }
}