Код контролеруsrc/Controller/SecurityController.php at line 33

public function login(Request $request, AuthenticationUtils $helper): Response
{
    // if user is already logged in, don't display the login page again
    if ($this->getUser()) {
        return $this->redirectToRoute('blog_index');
    }

    // this statement solves an edge-case: if you change the locale in the login
    // page, after a successful login you are redirected to a page in the previous
    // locale. This code regenerates the referrer URL whenever the login page is
    // browsed, to ensure that its locale is always the current one.
    $this->saveTargetPath($request->getSession(), 'main', $this->generateUrl('admin_index'));

    return $this->render('security/login.html.twig', [
        // last username entered by the user (if any)
        'last_username' => $helper->getLastUsername(),
        // last authentication error (if any)
        'error' => $helper->getLastAuthenticationError(),
    ]);
}

Код шаблону Twigtemplates/security/login.html.twig at line 1