code: private function login(): Response
      {
          $request = $this->container->get('request_stack')->getCurrentRequest();
  
          if (null === $request) {
              throw new \RuntimeException('The request stack did not contain a request');
          }
  
          if ('tl_login' !== $request->request->get('FORM_SUBMIT')) {
              return $this->render('login.html.twig');
          }
  
          $installTool = $this->container->get('contao.install_tool');
  
          $verified = password_verify(
              $request->request->get('password'),
              $installTool->getConfig('installPassword')
          );
  
          if (!$verified) {
              $installTool->increaseLoginCount();
  
              return $this->render('login.html.twig', [
                  'error' => $this->trans('invalid_password'),
              ]);
          }
  
          $installTool->resetLoginCount();
          $this->container->get('contao.install_tool_user')->setAuthenticated(true);
  
          return $this->getRedirectResponse();
      }
docs: Renders a form to log in.
  
  @throws \RuntimeException
  
  @return Response|RedirectResponse