HTTP authentication via PHP

<?php
// Http authentication code by w3tools.info
$user = "myuser"; //username here
$pass = "mypass"; //password here
if (!isset($_SERVER['PHP_AUTH_USER']) || !isset($_SERVER['PHP_AUTH_PW']) || $_SERVER['PHP_AUTH_USER']!=$user || $_SERVER['PHP_AUTH_PW']!=$pass){
    header('WWW-Authenticate: Basic realm="Enter password to access this page."');
    header('HTTP/1.0 401 Unauthorized');
    echo"You must be logged in";
    exit;
}
# Your protected contents go here !!
?>