title

/**
* Implements hook_preprocess_HOOK().
*/
function MYMODULE_preprocess_html(&$variables) {
 $variables['head_title']['title'] = 'new title';
}

/**
* Implements hook_preprocess_HOOK().
*/
function EXAMPLE_preprocess_page_title(&$variables) {
 $current_path = \Drupal::service('path.current')->getPath();
 if ($current_path == '/user/login') {
   $variables['title'] = '