/** Shows a browser URL to authorize this app to act as this user. */
  public void requestOauthSession(String scopes, String team) throws Exception {
    if (sessionFactory == null) {
      sessionFactory = new OAuthSessionFactory(slackApi);
      sessionFactory.start();
    }

    HttpUrl authorizeUrl = sessionFactory.newAuthorizeUrl(scopes, team, session -> {
      initOauthSession(session);
      System.out.printf("session granted: %s\n", session);