gistfile1.php

<?php

function do_auth() {
    // prompt for password
    header('WWW-Authenticate: Basic realm="pbrisbin dot com"');
    header('HTTP/1.0 401 Unauthorized');

    // if user cancels
    header('Content-type: text/plain');
    echo 'Not authorized.';
    exit;
}

function authenticate($_valid_users) {
    // credentials not known
    if (!isset($_SERVER['PHP_AUTH_USER']))
        do_auth();

    $user = $_SERVER['PHP_AUTH_USER'];
    $pass = $_SERVER['PHP_AUTH_PW'];

    // user not known
    if (!isset($_valid_users[$user]))
        do_auth();

    // bad password
    if ($_valid_users[$user] != $pass)
        do_auth();
}

?>