Building custom XML-RPC methods in WordPress

wp-xml-rpc.php

<?php
// Include the XML-RPC files
include_once(ABSPATH . WPINC . '/class-IXR.php');
include_once(ABSPATH . WPINC . '/class-wp-xmlrpc-server.php');

class my_xmlrpc extends wp_xmlrpc_server {
	function __construct() {
		// This filter will add the new methods we're building
		add_filter('xmlrpc_methods', array($this, 'my_xmlrpc_methods'));
		parent::__construct();
	}

	function my_xmlrpc_methods($methods) {
		$methods += array(
			// Methods here.
			'my.login_verify' => 'this:my_login_verify'
		);

		return $methods;
	}

	/*
	 * The Methods
	 */

	function my_login_verify($args) {

		// ALWAYS escape $args before using them!
		$this->escape($args);

		$username  = $args[0];
		$password   = $args[1];
		if ( !$user = $this->login($username, $password) )
			return $this->error;

		return true;
	}
}

// Make this the class we use!
add_filter('wp_xmlrpc_server_class', create_function('', 'return "my_xmlrpc";'));