Dart Requires Chilkat v11.0.0+

Validate a Google ID Token

See more OAuth2 Examples

Demonstrates how to verify the signature of a Google id 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.

  final http = CkHttp();

  // First get the public key we'll be needing..
  final String jwkStr;
  try {
    jwkStr = http.quickGetStr('https://www.googleapis.com/oauth2/v3/certs');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // We have the following:

  //     {
  //       "keys": [
  // 	{
  // 	  "kid": "e8732db06287515556213b80acbcfd08cfb302a9",
  // 	  "n": "4RIrO30287Wsq3gqXCMkUYMVAeI3H8...w2mbMNEBQ",
  // 	  "kty": "RSA",
  // 	  "e": "AQAB",
  // 	  "alg": "RS256",
  // 	  "use": "sig"
  // 	},
  // 	{
  // 	  "kid": "8462a71da4f6d611fc0fecf0fc4ba9c37d65e6cd",
  // 	  "e": "AQAB",
  // 	  "n": "xT_ngLZNmT5GBtJZeTB...Ft4gK0eoFi0d3l8bcw",
  // 	  "alg": "RS256",
  // 	  "use": "sig",
  // 	  "kty": "RSA"
  // 	}
  //       ]
  //     }

  final json = CkJsonObject();
  json.load(jwkStr);

  // -------------------------------------------------

  // Load the following..

  //  {
  //   "access_token": "ya29.a0...0f",
  //   "expires_in": 3599,
  //   "scope": "openid https://www.googleapis.com/auth/userinfo.email",
  //   "token_type": "Bearer",
  //   "id_token": "eyJhb...o5nQ"
  // }

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

  // Get the id_token;
  final sbIdToken = CkStringBuilder();
  sbIdToken.append(jsonToken.stringOf('id_token'));

  // Get the signature in base64url format.
  // The header + payload remains in sbIdToken.
  final sigB64Url = sbIdToken.getAfterFinal('.', true);
  final headerPlusPayload = sbIdToken.getAsString();

  print(sigB64Url);
  print(headerPlusPayload);

  // ---------------------------------------------

  // Try validating with each cert's public key.
  // Hopefully one will be the key that verifies.

  final rsa = CkRsa();
  rsa.encodingMode = 'base64url';

  final jsonKey = CkJsonObject();
  final pubKey = CkPublicKey();

  final numKeys = json.sizeOfArray('keys');
  var i = 0;
  while (i < numKeys) {
    json.i = i;

    json.objectOf2('keys[i]', jsonKey);

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

    print(i);
    print(pubKey.getPem(true));

    rsa.usePublicKey(pubKey);

    var bVerified = true;
    try {
      rsa.verifyStringENC(headerPlusPayload, 'sha256', sigB64Url);
    } on ChilkatException {
      bVerified = false;
    }
    print('bVerified = $bVerified');

    i++;
  }

  // The output is:

  // 0
  // -----BEGIN RSA PUBLIC KEY-----
  // MIIBCgKCAQEA4RIrO30287Wsq3gqXCMkUYMVAeI3H8LVE6IXR1krdFeGnZLiGUPw
  // cbkeVpXf3lmJdsStOg+jijces2DZCfPyIBiQuLYfxxmAZE6ErJ0QJFg1stwli2Pz
  // 9ncYhFoqi8pXr7kEzEJBTzX4thuw56ydbGsshSEznPXoerCJOc7UI2+n0wFCWQ4Y
  // LHbh/PrWt4vdadyUUUW/QpQHXQLdD8q/Qwqdj0O9zlJE7R6Elw2E9EqnHyIGu1hm
  // LxhqrTru1M18SUhONYbVskV/BCEdVKs//X96849HorWQDCAgVMWfGsdMVq55FAdJ
  // 680N5UmQDRynIZ4+PeNGN4S9iw2mbMNEBQIDAQAB
  // -----END RSA PUBLIC KEY-----
  // 
  // bVerified = True
  // 1
  // -----BEGIN RSA PUBLIC KEY-----
  // MIIBCgKCAQEAxT/ngLZNmT5GBdkLtJZjNeTB+8B5yWgrq/e5eMZ1hrZhcmLK+dSn
  // IkpOPV8/OekV67EnQ7I4II2rcNJnHGrGKZziXO3XN2gtUHE+mBJC99oULSbX/QwB
  // Kz7gC/IBPq9EuxTt6Oq6fPkVQ9DbRIgWJSEGBF/KRaNl3kyAlIZfpY7XgHyJTTv8
  // E7yAcYKPR+36gzdl+ps0sDLKzUuAtZNq8llK0u80z6AtAUIYwWdkEhM9upy6keKI
  // TasIxcsO7M6kZPINUSbh6t5VAm8FuqRmxpgg+9c9/GQSGd89InVypoVzWLQ+wOGg
  // 5G4H6JqIgtj0TRFt4gK0eoFi2U0d3l8bcwIDAQAB
  // -----END RSA PUBLIC KEY-----
  // 
  // bVerified = False
}