Dart Requires Chilkat v10.1.2+

HMRC OAuth2 Access Token

See more OAuth2 Examples

Demonstrates how to get an HMRC OAuth2 access token from a desktop (installed) application or script. This example gets an HMRC MTD VAT read/write access token. Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // To further clarify, see OAuth 2.0 Authorization Flow

  final oauth2 = CkOAuth2();

  // This should be the port in the localhost callback URL for your app.
  // Important: Make sure the callback URI in your HMRC developer app 
  // is exactly "http://localhost:3017/".  Don't forget the ending "/" char.
  // The callback URL would look like "http://localhost:3017/" if the port number is 3017.

  // IMPORTANT: Don't forget to setup your HMRC application to use the Redirect URI "http://localhost:3017/" as shown
  // here: Configure Redirect URI for HMRC application
  oauth2.listenPort = 3017;

  oauth2.authorizationEndpoint = 'https://test-api.service.hmrc.gov.uk/oauth/authorize';
  oauth2.tokenEndpoint = 'https://test-api.service.hmrc.gov.uk/oauth/token';

  // Replace with your actual client ID
  oauth2.clientId = 'HMRC-CLIENT-ID';

  // The scopes are documented in the HMRC reference documentation for each API.
  // This example gets a read/write access token for the HMRC MTD VAT API.
  oauth2.scope = 'read:vat write:vat';

  // Begin the OAuth2 Authorization code 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 default browser on the system and navigate to the url.
  // The LaunchBrowser method was added in Chilkat v10.1.2.
  try {
    oauth2.launchBrowser(url);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Wait for the user to approve or deny authorization in the browser.
  var numMsWaited = 0;
  while ((numMsWaited < 90000) && (oauth2.authFlowState < 3)) {
    oauth2.sleepMs(100);
    numMsWaited += 100;
  }

  // If the browser does not respond within the specified time, AuthFlowState will be:
  // 
  // 1: Waiting for Redirect – The OAuth2 background thread is waiting for the browser's redirect request.
  // 2: Waiting for Final Response – The thread is awaiting the final access token response.
  // In either case, cancel the background task initiated by StartAuth.

  if (oauth2.authFlowState < 3) {
    oauth2.cancel();
    print('No response from the browser!');
    return;
  }

  // Check AuthFlowState to determine if authorization was granted, denied, or failed:
  // 
  // 3: Success – OAuth2 flow completed, the background thread exited, and the successful response is in AccessTokenResponse.
  // 4: Access Denied – OAuth2 flow completed, the background thread exited, and the error response is in AccessTokenResponse.
  // 5: Failure – OAuth2 flow failed before completion, the background thread exited, and error details are in FailureInfo.

  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;
  }

  print('OAuth2 authorization granted!');
  print('Access Token = ${oauth2.accessToken}');

  // Get the full JSON response:
  final json = CkJsonObject();
  json.load(oauth2.accessTokenResponse);
  json.emitCompact = false;
  print(json.emit());

  // The JSON response looks like this:

  // {
  //   "token_type": "Bearer",
  //   "scope": "user_impersonation",
  //   "expires_in": "3599",
  //   "ext_expires_in": "0",
  //   "expires_on": "1524783438",
  //   "not_before": "1524779538",
  //   "resource": "https://mydomain.api.crm.dynamics.com",
  //   "access_token": "...",
  //   "refresh_token": "...",
  //   "id_token": "..."
  // }

  // If an "expires_on" member does not exist, then add the JSON member by
  // getting the current system date/time and adding the "expires_in" seconds.
  // This way we'll know when the token expires.
  if (!json.hasMember('expires_on')) {
    final dtExpire = CkDateTime();
    dtExpire.setFromCurrentSystemTime();
    dtExpire.addSeconds(json.intOf('expires_in'));
    json.appendString('expires_on', dtExpire.getAsUnixTimeStr(false));
  }

  print(json.emit());

  // Save the JSON to a file for future requests.
  final fac = CkFileAccess();
  fac.writeEntireTextFile('qa_data/tokens/hmrc.json', json.emit(), 'utf-8', false);
}