static {
        try {
            DATA_STORE_FACTORY = new FileDataStoreFactory(DATA_STORE_DIR);
            HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
        } catch (Throwable t) {
            t.printStackTrace();
        }
    }


    private Credential authorize() throws IOException {
    // load client secrets
    GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(
            Thread.currentThread().getContextClassLoader().getResourceAsStream("credentials.json")));
    // set up authorization code flow
    GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(HTTP_TRANSPORT, JSON_FACTORY,
            clientSecrets, SCOPES).setDataStoreFactory(DATA_STORE_FACTORY).build();
    // authorize
    return new AuthorizationCodeInstalledApp(flow, new LocalServerReceiver()).authorize("user");
}