code: protected void onAuthorization(AuthorizationCodeRequestUrl authorizationUrl) throws IOException {
      String url = authorizationUrl.build();
      Preconditions.checkNotNull(url);
      browser.browse(url);
    }
docs: Handles user authorization by redirecting to the OAuth 2.0 authorization server.
  
  <p>
  Default implementation is to call {@code browse(authorizationUrl.build())}. Subclasses may
  override to provide optional parameters such as the recommended state parameter. Sample
  implementation:
  </p>
  
  <pre>
  &#64;Override
  protected void onAuthorization(AuthorizationCodeRequestUrl authorizationUrl) throws IOException {
  authorizationUrl.setState("xyz");
  super.onAuthorization(authorizationUrl);
  }
  </pre>
  
  @param authorizationUrl authorization URL
  @throws IOException I/O exception