this.port = port;
  }

  /** See https://api.slack.com/docs/oauth. */
  public HttpUrl authorizeUrl(String scopes, HttpUrl redirectUrl, ByteString state, String team) {
    HttpUrl.Builder builder = baseUrl.newBuilder("/oauth/authorize")
        .addQueryParameter("client_id", clientId)
        .addQueryParameter("scope", scopes)
        .addQueryParameter("redirect_uri", redirectUrl.toString())
        .addQueryParameter("state", state.base64());

  /** 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);