the first think you must to do , is create a form that post a field name pass to the secret.php file.
example of form:
<form method="post" action="secret.php">
<input type="password" name="pass" size="5">
</form>
then create a secret.php file like :
<?
$MYpass="EnterYourSecretPassHere";
if ($pass==$MYpass) {
$fp=fopen("http://YOURSECRETHTMLFILE","r");
$data="";
while($data=fgets($fp,4096)) {
echo $data;
}
fclose($fp);
} else {
echo "<body><h1>ACCESS DENIED</h1></body>";
}
?>
on MYpass variable you add the secret password you want and on the YOURSECRETHTMLFILE you just enter the url of the html ( for example http://www.test.com/blah.html ) .
With this way in your address bar it's only show the secret.php file 🙂