Dart

Get POP3 GMail OAuth2 Access Token for Desktop App

See more GMail SMTP/IMAP/POP Examples

Demonstrates how to get a POP3 GMail OAuth2 access token from a desktop application or script.

This example requires a browser window to be displayed to allow the GMail account owner to authorize the access. The code for displaying the web browser is omitted. Suggestions for a few programming languages are provided in code comments. To complete this example, you will need to find out how to display a web browser and navigate to the URL returned by the call to oauth2.StartAuth.

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.

  final oauth2 = CkOAuth2();

  // For Google OAuth2, set the listen port equal to the port used
  // in the Authorized Redirect URL for the Client ID.
  // For example, in this case the Authorized Redirect URL would be http://localhost:55568/
  // Your app should choose a port not likely not used by any other application.
  oauth2.listenPort = 55568;

  oauth2.authorizationEndpoint = 'https://accounts.google.com/o/oauth2/v2/auth';
  oauth2.tokenEndpoint = 'https://www.googleapis.com/oauth2/v4/token';

  // Replace these with actual values.
  oauth2.clientId = 'GOOGLE-CLIENT-ID';
  oauth2.clientSecret = 'GOOGLE-CLIENT-SECRET';

  oauth2.codeChallenge = true;
  oauth2.codeChallengeMethod = 'S256';

  // See https://developers.google.com/gmail/api/auth/scopes for a list of GMail scopes.
  // This is the full-permissions scope for GMail, which is sufficient for all POP3 operations to pop.gmail.com
  oauth2.scope = 'https://mail.google.com/';

  // Important note about GMail scope for sending email:
  // If the SMTP protocol is used for sending, then the full GMail scope is required: "https://mail.google.com/"
  // Here is an example that sends GMail via the SMTP protocol:  Send GMail using SMTP
  // If the GMail REST API is used, then the more restrictive Gmail scope can be used:  "https://www.googleapis.com/auth/gmail.send"
  // Here is an example that sends GMail using the GMail REST API: Send GMail using REST API

  // Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
  final String url;
  try {
    url = oauth2.startAuth();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Launch the system's default browser navigated to the URL.
  try {
    oauth2.launchBrowser(url);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Now wait for the authorization.
  // We'll wait for a max of 30 seconds.
  var numMsWaited = 0;
  while ((numMsWaited < 30000) && (oauth2.authFlowState < 3)) {
    oauth2.sleepMs(100);
    numMsWaited += 100;
  }

  // If there was no response from the browser within 30 seconds, then 
  // the AuthFlowState will be equal to 1 or 2.
  // 1: Waiting for Redirect. The OAuth2 background thread is waiting to receive the redirect HTTP request from the browser.
  // 2: Waiting for Final Response. The OAuth2 background thread is waiting for the final access token response.
  // In that case, cancel the background task started in the call to StartAuth.
  if (oauth2.authFlowState < 3) {
    oauth2.cancel();
    print('No response from the browser!');
    return;
  }

  // Check the AuthFlowState to see if authorization was granted, denied, or if some error occurred
  // The possible AuthFlowState values are:
  // 3: Completed with Success. The OAuth2 flow has completed, the background thread exited, and the successful JSON response is available in AccessTokenResponse property.
  // 4: Completed with Access Denied. The OAuth2 flow has completed, the background thread exited, and the error JSON is available in AccessTokenResponse property.
  // 5: Failed Prior to Completion. The OAuth2 flow failed to complete, the background thread exited, and the error information is available in the FailureInfo property.
  if (oauth2.authFlowState == 5) {
    print('OAuth2 failed to complete.');
    print(oauth2.failureInfo);
    return;
  }

  if (oauth2.authFlowState == 4) {
    print('OAuth2 authorization was denied.');
    print(oauth2.accessTokenResponse);
    return;
  }

  if (oauth2.authFlowState != 3) {
    print('Unexpected AuthFlowState:${oauth2.authFlowState}');
    return;
  }

  // Save the full JSON access token response to a file.
  final sbJson = CkStringBuilder();
  sbJson.append(oauth2.accessTokenResponse);
  sbJson.writeFile('qa_data/tokens/gmail_pop3.json', 'utf-8', false);

  // The saved JSON response looks like this:

  // 	{
  // 	 "access_token": "ya39.Ci-XA_C5bGgRDC3UaD-h0_NeL-DVIQnI2gHtBBBHkZzrwlARkwX6R3O0PCDEzRlfaQ",
  // 	 "token_type": "Bearer",
  // 	 "expires_in": 3600,
  // 	 "refresh_token": "1/r_2c_7jddspcdfesrrfKqfXtqo08D6Q-gUU0DsdfVMsx0c"
  // 	}
  // 
  print('OAuth2 authorization granted!');
  print('Access Token = ${oauth2.accessToken}');
}