Use a simple PHP script with a static username and password and maybe a javascript prompt form, or standard HTML prompt form.
<?php
$username = "myusername";
$password = "mypassword";
if (!isset($_POST['submit'])) {
?>
<form method="POST" action="<?=$_SERVER['PHP_SELF']?>">
Username: <input type="text" name="username"><br/>
Password: <input type="password" name="password"><br/>
<input type="submit" name="submit" value="Login">
<?php
} else {
if ($_POST['username'] == $username && $_POST['password'] == $password) {
echo "<a href="privatepage.html">Click to continue...</a>";
}
}
?> Or something like that. Not very secure though. But works.