auth.php

<?php
require('creds.php');

if( isset($creds[$_POST['user']]) && ($creds[$_POST['user']] == md5($_POST['pass'])) ) {
  echo "Authenticated";
} else {
    echo <<<_eoi_
<form action="" method="POST">
    <input name="user" type="text" />
    <input name="pass" type="password" />
    <input type="submit" />
</form>
_eoi_;
}

creds.php

<?php

$creds = array( 
    'gordian' => 'ea702ba4205cb37a88cc84851690a7a5'
);