Dart

Google Sheets Refresh an Expired Access Token

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Demonstrates how to refresh an expired access token. If a Google Sheets REST API call results in a 401 "unauthorized" response, then it is likely the access token expired. An application should be able to automatically refresh the access token with no user interaction and then re-try the request with the newly obtained access token. 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.

  // It is assumed we previously obtained an OAuth2 access token.
  // This example loads the JSON access token file 
  // saved by this example: Get Google Sheets OAuth2 Access Token

  final jsonToken = CkJsonObject();
  try {
    jsonToken.loadFile('qa_data/tokens/googleSheets.json');
  } on ChilkatException {
    print('Failed to load googleSheets.json');
    return;
  }

  // The access token JSON looks like this:

  // 	{ 
  // 	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
  // 	 "token_type": "Bearer",
  // 	 "expires_in": 3600,
  // 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
  // 	}
  // 

  final oauth2 = CkOAuth2();

  oauth2.tokenEndpoint = 'https://www.googleapis.com/oauth2/v4/token';

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

  // Get the "refresh_token"
  oauth2.refreshToken = jsonToken.stringOf('refresh_token');

  // Send the HTTP POST to refresh the access token..
  try {
    oauth2.refreshAccessToken();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // The response contains a new access token, but we must keep
  // our existing refresh token for when we need to refresh again in the future.
  jsonToken.updateString('access_token', oauth2.accessToken);

  // Save the new JSON access token response to a file.
  final sbJson = CkStringBuilder();
  jsonToken.emitCompact = false;
  jsonToken.emitSb(sbJson);
  sbJson.writeFile('qa_data/tokens/googleSheets.json', 'utf-8', false);

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