whmcs-php provides PHP bindings for the WHMCS API.
<?php
include_once 'lib/whmcs.php';
define('WHMCS_URL', 'http://example.com/includes/api.php');
define('WHMCS_USERNAME', 'someusername');
define('WHMCS_PASSWORD', 'c4ca4238a0b923820dcc509a6f75849b'); // md5 hash
var_dump(WHMCS_Client::get_clients_details(array('clientid' => '1')));
See the lib/whmcs/ in this repo for usage details.
Copyright (c) 2011 DotBlock.com, see LICENSE in this repo for details.