Protect your page by HTTP Authentication: Basic

<?php
    $login='admin';
    $md5_pass = md5('admin');
    if (($_SERVER["PHP_AUTH_USER"] != $login) or (md5($_SERVER["PHP_AUTH_PW"]) != $md5_pass)) {
        header("WWW-Authenticate: Basic realm=\"Please login! HTTP/1.0 401 Unauthorized");
        die;
    }
    // if logined
    echo "OK!...";
?>