MCAuth

Minecraft PHP Authentication for new Mojang Yggdrasil (http://wiki.vg/Authentication) authentication scheme, _(*1)

Example:

<?php
include("MCAuth.class.php");
$MCAuth = new MCAuth();
if ($MCAuth->authenticate('username or email', 'password') == TRUE) {
    echo $MCAuth->account['id'];            // hexadecimal user ID
    echo $MCAuth->account['username'];      // account username
    echo $MCAuth->account['token'];         // access token
} else {
    echo $MCAuth->autherr;                  // print error
}

Warning!

Mojang authentication system permits only one active session as reported in the wiki: "Only the one with the latest session ID for your account are allowed to join servers.", so you will be disconnected from the server where you are playing if you try to login via MCAuth., _(*2)