redirect-home-page.php

use Drupal\Core\Form\FormStateInterface;
function hook_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  switch ($form_id) {
    // Alter login form and add own custom submit handler.
    case 'user_login_form':
      $form['#submit'][] = '_statefair_user_login_form_submit';
      break;
  }
}

/**
 * Custom submit handler for login form.
 */
function _user_login_form_submit($form, FormStateInterface $form_state) {
  // Set redirect to login form.
  $form_state->setRedirect('<front>');
}