generate method

@override Future<Token> generate()

generate a OAuth2 refresh token from JWT credentials

Implementation

@override
Future<Token> generate() async {
  final now = DateTime.now();

  final jsonWebKey = JsonWebKey.fromPem(jwtCredentials.settings.privateKey);

  final keyPair = jsonWebKey.cryptoKeyPair;

  final privateKey = keyPair.privateKey!;

  final signer = privateKey.createSigner(algorithms.signing.rsa.sha256);

  final header = Util.base64GCloudString('{"alg":"RS256","typ":"JWT"}');

  final claim = Util.base64GCloudString('''{
    "iss": "${jwtCredentials.settings.clientEmail}",
    "scope": "${jwtCredentials.scope}",
    "aud": "https://www.googleapis.com/oauth2/v4/token",
    "exp": ${Util.unixTimeStamp(now.add(Duration(minutes: 60)))},
    "iat": ${Util.unixTimeStamp(now)}
}''');

  final signature = signer.sign('$header.$claim'.codeUnits);

  final jwt = '$header.$claim.${Util.base64GCloudList(signature.data)}';

  final OAuthClient oAuthClient = OAuthClient(dio);

  return await oAuthClient.getToken({
    'grant_type': 'urn:ietf:params:oauth:grant-type:jwt-bearer',
    'assertion': jwt
  });
}