Dart

OAuth2 for a GMail using a JSON Service Account Key

See more GMail SMTP/IMAP/POP Examples

This example shows how to obtain an OAuth2 access token for Gmail using a Google Service Account and a JSON private key. Once acquired, the access token can be used to send emails. Remember, upon token expiration, this process needs to be repeated to obtain a new token. Note: This procedure is specific to OAuth2 with Google Service Account keys. Dart

import 'package:chilkat/chilkat.dart';

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

  // --------------------------------------------------------------------------------
  // 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
  // --------------------------------------------------------------------------------

  // First load the JSON key into a string.
  final fac = CkFileAccess();
  final String jsonKey;
  try {
    jsonKey = fac.readEntireTextFile('qa_data/googleApi/chilkat25-b4214220e565.json', 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // A Google service account JSON private key looks like this:

  // {
  //   "type": "service_account",
  //   "project_id": "chilkat25",
  //   "private_key_id": "b4214220f565881e19eeb97c2699bf5a0d1e3e0b",
  //   "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvQ...NXcM=\n-----END PRIVATE KEY-----\n",
  //   "client_email": "chilkatsvc@chilkat25.iam.gserviceaccount.com",
  //   "client_id": "109122032928932715958",
  //   "auth_uri": "https://accounts.google.com/o/oauth2/auth",
  //   "token_uri": "https://oauth2.googleapis.com/token",
  //   "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
  //   "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/chilkatsvc%40chilkat25.iam.gserviceaccount.com",
  //   "universe_domain": "googleapis.com"
  // }

  final gAuth = CkAuthGoogle();
  gAuth.jsonKey = jsonKey;

  // Specify a scope.
  gAuth.scope = 'https://mail.google.com/';

  // Request an access token that is valid for this many seconds.
  gAuth.expireNumSeconds = 3600;

  // When using a Google Workspace account with Gmail APIs, a service account can impersonate a user 
  // via a process called domain-wide delegation � and the "sub" claim in the JWT is what enables this.
  // Domain-wide delegation allows a Google Workspace administrator to authorize a service account to 
  // act on behalf of any user in the domain, without user interaction.

  // This is required for server-to-server access to user data � such as reading/sending Gmail from a background service.
  // This is your company email address.
  gAuth.subEmailAddress = 'info@chilkat.xyz';

  // Connect to www.googleapis.com using TLS
  final tlsSock = CkSocket();
  try {
    tlsSock.connect('www.googleapis.com', 443, true, 5000);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Send the request to obtain the access token.
  try {
    gAuth.obtainAccessToken(tlsSock);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Examine the access token:
  final accessToken = gAuth.accessToken;
  print('Access Token: $accessToken');

  // Sample output:
  // ya29.a0AW4XtxjGTD67Z8 .... IRw0218

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

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

  // Set the properties for the GMail SMTP server:
  mailman.smtpHost = 'smtp.gmail.com';
  mailman.smtpPort = 587;
  mailman.startTLS = true;

  mailman.smtpUsername = 'info@chilkat.xyz';
  mailman.oAuth2AccessToken = accessToken;

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

  email.subject = 'This is a test';
  email.body = 'This is a test';
  email.from = 'Chilkat Test <info@chilkat.xyz>';
  email.addTo('Chilkat Software', 'info@chilkatsoft.com');
  // To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

  try {
    mailman.sendEmail(email);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    mailman.closeSmtpConnection();
  } on ChilkatException {
    print('Connection to SMTP server not closed cleanly.');
  }

  print('Successfully sent email using Gmail with a service account key.');
}