Auth.php

<?php

class Auth
{
    protected $realm = 'My Realm';
    protected $user = array();
    protected $isAuthenticated = false;

    protected $nonce = null;
    protected $digest = null;

    function __construct($options)
    {
        $this->nonce = uniqid();
        $this->user  = $options['user'];
        $this->realm = $options['realm'];

        $this->digest = $this->getDigest();

        if($this->digest != null && $this->validate()) {
            $this->isAuthenticated = true;
        }
    }

    public function login()
    {
        header('WWW-Authenticate: Digest realm="' . $this->realm . '",qop="auth",nonce="' . $this->nonce . '",opaque="' . md5($this->realm) . '"');
        header('HTTP/1.0 401 Unauthorized');
    }

    public function logout()
    {
        header('HTTP/1.1 401 Unauthorized');
        unset($_SERVER['PHP_AUTH_DIGEST']);
        $this->isAuthenticated = false;

        return true;
    }

    protected function validate()
    {
        $digestParse = $this->digestParse($this->digest);
        $a1 = md5("{$this->user['username']}:{$this->realm}:{$this->user['password']}");
        $a2 = md5("{$_SERVER['REQUEST_METHOD']}:{$digestParse['uri']}");
        $response = md5("{$a1}:{$digestParse['nonce']}:{$digestParse['nc']}:{$digestParse['cnonce']}:{$digestParse['qop']}:{$a2}");

        if($digestParse['response'] != $response) {
            return false;
        }

        return true;
    }

    protected function getDigest()
    {
        if (isset($_SERVER['PHP_AUTH_DIGEST'])) {
            $digest = $_SERVER['PHP_AUTH_DIGEST'];
        } elseif (isset($_SERVER['HTTP_AUTHENTICATION'])) {
            if (strpos(strtolower($_SERVER['HTTP_AUTHENTICATION']),'digest')===0) {
                $digest = substr($_SERVER['HTTP_AUTHORIZATION'], 7);
            }
        } else {
            return false;
        }

        return $digest;
    }

    protected function digestParse($digest)
    {
        // protect against missing data
        $needed_parts = array('nonce'=>1, 'nc'=>1, 'cnonce'=>1, 'qop'=>1, 'username'=>1, 'uri'=>1, 'response'=>1);
        $data = array();

        preg_match_all('@(\w+)=(?:(?:")([^"]+)"|([^\s,$]+))@', $digest, $matches, PREG_SET_ORDER);

        foreach ($matches as $m) {
            $data[$m[1]] = $m[2] ? $m[2] : $m[3];
            unset($needed_parts[$m[1]]);
        }

        return $needed_parts ? false : $data;
    }

    public function isAuthenticated()
    {
        return $this->isAuthenticated;
    }
}