code: protected void onAuthorization(HttpServletRequest req, HttpServletResponse resp,
        AuthorizationCodeRequestUrl authorizationUrl) throws ServletException, IOException {
      resp.sendRedirect(authorizationUrl.build());
    }
docs: Handles user authorization by redirecting to the OAuth 2.0 authorization server.
  
  <p>
  Default implementation is to call {@code resp.sendRedirect(authorizationUrl.build())}.
  Subclasses may override to provide optional parameters such as the recommended state parameter.
  Sample implementation:
  </p>
  
  <pre>
  &#64;Override
  protected void onAuthorization(HttpServletRequest req, HttpServletResponse resp,
  AuthorizationCodeRequestUrl authorizationUrl) throws ServletException, IOException {
  authorizationUrl.setState("xyz");
  super.onAuthorization(req, resp, authorizationUrl);
  }
  </pre>
  
  @param authorizationUrl authorization code request URL
  @param req HTTP servlet request
  @throws ServletException servlet exception
  @since 1.11