gistfile1.phtml

<?php
/** Check for a valid GET parameter before rendering the rest of the page
  * otherwise send a 404 header to prevent bots
  */
if(!isset($_GET['YOUR_FAVORITE_PARAMETER']))
{
	header("HTTP/1.0 404 Not Found");
	exit;
}
/*

SNIP

*/
?>
<form name="loginform" id="loginform" action="<?php echo esc_url( site_url( 'wp-login.php?YOUR_FAVORITE_PARAMETER=1', 'login_post' ) ); ?>" method="post">