docs: public void requestAuthorization(HttpServletRequest req, HttpServletResponse res, String loginFormURL)
      throws IOException {
  
          CmsHttpAuthenticationSettings httpAuthenticationSettings = OpenCms.getSystemInfo().getHttpAuthenticationSettings();
  
          if (loginFormURL == null) {
              if (httpAuthenticationSettings.useBrowserBasedHttpAuthentication()) {
                  // HTTP basic authentication is used
                  res.setHeader(
                      CmsRequestUtil.HEADER_WWW_AUTHENTICATE,
                      "BASIC realm=\"" + OpenCms.getSystemInfo().getOpenCmsContext() + "\"");
                  res.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
                  return;
  
              } else if (httpAuthenticationSettings.getFormBasedHttpAuthenticationUri() != null) {
                  loginFormURL = httpAuthenticationSettings.getFormBasedHttpAuthenticationUri();
              } else {
                  LOG.error(
                      Messages.get().getBundle().key(
                          Messages.ERR_UNSUPPORTED_AUTHENTICATION_MECHANISM_1,
                          httpAuthenticationSettings.getBrowserBasedAuthenticationMechanism()));
                  res.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
                  return;
              }
          }
  
          if (LOG.isDebugEnabled()) {
              LOG.debug(
                  Messages.get().getBundle().key(
                      Messages.LOG_AUTHENTICATE_PROPERTY_2,
                      loginFormURL,
                      req.getRequestURI()));
          }
          // finally redirect to the login form
          res.sendRedirect(loginFormURL);
      }