Dart

Get OAuth 2.0 Access Token using G_SvcOauthAccessToken2

Obtains an OAUTH2 access token from the Google OAuth 2.0 Authorization Server using the G_SvcOauthAccessToken2 method. This is for Server to server applications using Google API's that need an access token. See https://developers.google.com/accounts/docs/OAuth2ServiceAccount Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example assumes 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
  // --------------------------------------------------------------------------------

  final http = CkHttp();

  // When a service account (Client ID) is created at https://code.google.com/apis/console/
  // Google will generate a P12 key.  This is a PKCS12 (PFX) file that you will download
  // and save.  The password to access the contents of this file is "notasecret".
  // NOTE: The Chilkat Pfx API provides the ability to load a PFX/P12 and re-save
  // with a different password.

  // Begin by loading the downloaded .p12 into a Chilkat certificate object:
  final cert = CkCert();
  try {
    cert.loadPfxFile('/myDir/API Project-1c43a291e2a1-notasecret.p12', 'notasecret');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // The next (and final) step is to request the access token.  Chilkat internally
  // does all the work of forming the JWT header and JWT claim set, encoding and
  // signing the JWT, and sending the access token request.
  // The application need only provide the inputs: The iss, scope(s), sub, and the
  // desired duration with a max of 3600 seconds (1 hour).
  // 
  // Each of these inputs is defined as follows 
  // (see https://developers.google.com/accounts/docs/OAuth2ServiceAccount
  // iss: The email address of the service account.
  // scope: A space-delimited list of the permissions that the application requests.
  // sub: The email address of the user for which the application is requesting delegated access.
  // numSec: The number of seconds for which the access token will be valid (max 3600).

  final claimParams = CkHashtable();

  // The required claim parameters that must be provided by the application are
  // the "iss" and "scope" params:
  claimParams.addStr('iss', '761326798069-r5mljlln1rd4lrbhg75efgigp36m78j5@developer.gserviceaccount.com');
  claimParams.addStr('scope', 'https://mail.google.com/');

  // The "sub" param is required if there is an email address, such as for a
  // Google Apps domain—if you use Google Apps for Work, where the administrator of the Google Apps domain 
  // can authorize an application to access user data on behalf of users in the Google Apps domain.
  // 
  // Comment out this line if there is no such email address.
  claimParams.addStr('sub', 'user@your-domain.com');

  // The "aud" parameter is optional.  If not set, it defaults to the value shown here:
  claimParams.addStr('aud', 'https://accounts.google.com/o/oauth2/token');

  final numSec = 3600;

  try {
    final accessToken = http.gSvcOauthAccessToken2(claimParams, numSec, cert);
    print('access token: $accessToken');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
  }
}