Change a google user password

change-user-pass.php

<?php
// composer require --no-dev google/apiclient
// composer require --no-dev google/apiclient-services
require_once __DIR__ . '/vendor/autoload.php';

$config = [
    // configure stuff here for Google_Client
];

$dir = new Google_Service_Directory(new Google_Client($config));
$user = $dir->users->get($username);
$user->setPassword($newpassword);
$dir->users->update($username, $user);