Dart

Verify a Google JWT Using Google's Public Key

See more Google APIs Examples

Demonstrates how to verify a JWT that was signed using Google's RSA private key.

This example verifies the RSA signature. It also does the following:

• Checks to see if the time constraints ("nbf" and "exp") are valid.
• Recovers the original JOSE header.
• Recovers the original claims JSON.

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.

  final http = CkHttp();
  final sbPubKeys = CkStringBuilder();

  try {
    http.quickGetSb('https://www.googleapis.com/oauth2/v3/certs', sbPubKeys);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(sbPubKeys.getAsString());

  // Here are the keys:

  // {
  //   "keys": [
  //     {
  //       "e": "AQAB",
  //       "n": "4bAT6C6EeX8Dspje3FrAXw-nnhNk04e1RmNa4kjc0CHf6Pk7ryARlwA-6YilyPABqQfYHx60s8oSnxvUVprFfQ2-Q8aAZO7bPKSxnoGlcKERL2oLNA4Msvc89N9Y5ycThZUplf_QC19e6jyYXN6Nz-UnJSCLrtQY8tVhhVRs61j4A2N_p-enAi-r704Qi1-v-DKV4eVRkClKViploo8NyjUaT9L4vbBssPCjyimJzsWnEe1fED5c4LnHeArYzA_FEn3JJotqDIz9t2VnvZNTMhizHEX4VnORlEWMEfR8n4CEHQx7PcQUOmfqyw08gWeXQl1-uTjtIGaE-sRIv9u_vQ",
  //       "kty": "RSA",
  //       "use": "sig",
  //       "alg": "RS256",
  //       "kid": "2af90e87be140c20038898a6efa11283dab6031d"
  //     },
  //     {
  //       "n": "nzGsrziOYrMVYMpvUZOwkKNiPWcOPTYRYlDSdRW4UpAHdWPbPlyqaaphYhoMB5DXrVxI3bdvm7DOlo-sHNnulmAFQa-7TsQMxrZCvVdAbyXGID9DZYEqf8mkCV1Ohv7WY5lDUqlybIk1OSHdK7-1et0QS8nn-5LojGg8FK4ssLf3mV1APpujl27D1bDhyRb1MGumXYElwlUms7F9p9OcSp5pTevXCLmXs9MJJk4o9E1zzPpQ9Ko0lH9l_UqFpA7vwQhnw0nbh73rXOX2TUDCUqL4ThKU5Z9Pd-eZCEOatKe0mJTpQ00XGACBME_6ojCdfNIJr84Y_IpGKvkAEksn9w",
  //       "use": "sig",
  //       "kid": "87bbe0815b064e6d449cac999f0e50e72a3e4374",
  //       "e": "AQAB",
  //       "alg": "RS256",
  //       "kty": "RSA"
  //     }
  //   ]
  // }

  // -------------------------------------------------------------------------------------------
  // Replace this with your actual token.
  // This sample token contains a kid that does not match any of the above Google public keys.
  // -------------------------------------------------------------------------------------------
  final token = 'eyJhbGciOiJSUzI1NiIsImtpZCI6IjQyZmY5MGQ3ZDM0OGM5NzM4MWE3YzExOWVmMWY1MzI0ZWEzZjViZWIifQ.eyJpc3MiOiJodHRwczovL2FjY291bnRzLmdvb2dsZS5jb20iLCJzdWIiOiIxMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExIiwiaWF0IjoxNjExMTE1MTQzLCJleHAiOjE2MTEyMDE1NDMsImF1ZCI6IjQyOTc1NzExNTE0ODg0OSJ9.pLem5i0bx3M7lJYj7jKv2Nq7c07X5YpZz-x1uM5RniW-v4LsX-lKIVvOq2x3-WoPqkzLXJfP0kG0dx1uD2q1NfFQK60YwKH4FnFtB6INnUP1dRVpP9_pTTKyAE28I3s5Tay4PbPdrCl7ZLCIJzCfpCW1TiWeVoPjp5HgZKTBHdP_sEkN_yO5dQerQXAkFJkV3kNgF9jI3ayT-KPqOIH6GVoWXjHFDyA2EYgJPEFRo5WSe6XycJ85p5duwT-OoBcb_kJZG9PxYd91eHlPCzp8vGxzIb2dVROCBxyM8e8W0cd9v15hfmpg9R-eG9vCM5y63ZLChZLFeHFx0Pd7hvAqfKg';

  final jwt = CkJwt();
  final header = jwt.getHeader(token);

  print(header);

  // Sample header:
  // {"alg":"RS256","kid":"87bbe0815b064e6d449cac999f0e50e72a3e4374"}

  // Load the public key matching the "kid" into a Chilkat public key object, then verify..

  final json = CkJsonObject();
  json.load(header);
  final kid = json.stringOf('kid');

  print('kid = $kid');

  final jsonPubKeys = CkJsonObject();
  jsonPubKeys.loadSb(sbPubKeys);

  final CkJsonObject jsonKey;
  try {
    jsonKey = jsonPubKeys.findRecord('keys', 'kid', kid, true);
  } on ChilkatException {
    print('Did not find a matching public key based on the kid.');
    return;
  }

  print(jsonKey.emit());

  // Load the matching public key into a Chilkat public key object.
  final pubKey = CkPublicKey();

  try {
    pubKey.loadFromString(jsonKey.emit());
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // ----------------------------------------------------------------------------------------
  // Now we can validate the JWT using Google's public key as shown in this example:
  // (Except we use the public key obtained as shown above instead of a public key loaded from a PEM file.
  // 
  // See Verify JWT Using an RSA Public Key
}