SiteConfigureForm::submitForm

public SiteConfigureForm::submitForm(array &$form, FormStateInterface $form_state)

public function submitForm(array &$form, FormStateInterface $form_state) {
  $this->config('system.site')
    ->set('name', (string) $form_state->getValue('site_name'))
    ->set('mail', (string) $form_state->getValue('site_mail'))
    ->save(TRUE);

  $this->config('system.date')
    ->set('timezone.default', (string) $form_state->getValue('date_default_timezone'))
    ->set('country.default', (string) $form_state->getValue('site_default_country'))
    ->save(TRUE);

  $account_values = $form_state->getValue('account');

  // Enable update.module if this option was selected.
  $update_status_module = $form_state->getValue('update_status_module');
  if ($update_status_module[1]) {
    $this->moduleInstaller->install(array('file', 'update'), FALSE);

    // Add the site maintenance account's email address to the list of
    // addresses to be notified when updates are available, if selected.
    if ($update_status_module[2]) {
      // Reset the configuration factory so it is updated with the new module.
      $this->resetConfigFactory();
      $this->config('update.settings')->set('notification.emails', array($account_values['mail']))->save(TRUE);
    }
  }

  // We precreated user 1 with placeholder values. Let's save the real values.
  $account = $this->userStorage->load(1);
  $account->init = $account->mail = $account_values['mail'];
  $account->roles = $account->getRoles();
  $account->activate();
  $account->timezone = $form_state->getValue('date_default_timezone');
  $account->pass = $account_values['pass'];
  $account->name = $account_values['name'];
  $account->save();

  // Record when this install ran.
  $this->state->set('install_time', $_SERVER['REQUEST_TIME']);
}