PHP to create a WordPress admin user

add-user.php

<?php

require_once('wp-blog-header.php');
require_once('wp-includes/registration.php');

$username = 'spencer';
$password = 'f00b4rb4z!';
$email = '[email protected]';

if (!username_exists($username) && !email_exists($email)) {
  $user_id = wp_create_user($username, $password, $email);
  if (is_int($user_id)) {
    $user = new WP_User($user_id);
    $user->set_role('administrator');
  }
}