drupal/core/modules/basic_auth/basic_auth.module

<?php

/**
 * @file
 * Provides an HTTP Basic authentication provider.
 */

use Drupal\Core\Url;
use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Implements hook_help().
 */
function basic_auth_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.basic_auth':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The HTTP Basic Authentication module supplies an <a href="http://en.wikipedia.org/wiki/Basic_access_authentication">HTTP Basic authentication</a> provider for web service requests. This authentication provider authenticates requests using the HTTP Basic Authentication username and password, as an alternative to using Drupal\'s standard cookie-based authentication system. It is only useful if your site provides web services configured to use this type of authentication (for instance, the <a href=":rest_help">RESTful Web Services module</a>). For more information, see the <a href=":hba_do">online documentation for the HTTP Basic Authentication module</a>.', [':hba_do' => 'https://www.drupal.org/documentation/modules/basic_auth', ':rest_help' => (\Drupal::moduleHandler()->moduleExists('rest')) ? Url::fromRoute('help.page', ['name' => 'rest'])->toString() : '#']) . '</p>';
      return $output;
  }
}