This tutorial is vBulletin.org and cPublisher.com copywrited. All rights reserved.
Please ask permission in this thread to copy the tutorial. If granted, post a link that points to this page.

As you all know, using PHP-CGI is more secure then the ole Apache module flavour.
However, with PHP-CGI you cannot use anymore real user authentification, based on a .htaccess/.htpasswd file.

The fix is really easy (and secure), all you need is to have Apache mod_rewrite enabled.

Create a .htaccess file, with the content:
RewriteEngine On

... your RewriteCond/RewriteRules here ...

RewriteRule .* - [E=REMOTE_USER:%{HTTP:Authorization},L]
Make sure the line above is the last one in your .htaccess file, if you already have one in place.
Then, in your PHP file, use:
<?php

$auth = base64_decode(substr($_SERVER['REMOTE_USER'], 6));
if (strlen($auth) > 0 OR strcasecmp($auth, ':') > 0)
{
list($name, $password) = explode(':', $auth);
$_SERVER['PHP_AUTH_USER'] = $name;
$_SERVER['PHP_AUTH_PW'] = $password;

$user_authorized = true;
}
else
{
header('WWW-Authenticate: Basic realm="My Realm"');
header('HTTP/1.0 401 Unauthorized');
echo 'Go away!';
}

if ($user_authorized)
{
// do your thing here ...
}

?>
I needed this for the apc.php file, running on my server PHP 5.1.6 with FastCGI mode enabled.
For those who want to fix the apc.php file, find:
// authentication needed?
//
if (!USE_AUTHENTICATION) {
$AUTHENTICATED=1;
} else {
$AUTHENTICATED=0;
if (ADMIN_PASSWORD!='password' && ($MYREQUEST['LO'] == 1 || isset($_SERVER['PHP_AUTH_USER']))) {
Replace with:
// authentication needed?
//
if (!USE_AUTHENTICATION)
{
$AUTHENTICATED = 1;
}
else
{
$auth = base64_decode(substr($_SERVER['REMOTE_USER'], 6));
if (strlen($auth) > 0 OR strcasecmp($auth, ':') > 0)
{
list($name, $password) = explode(':', $auth);
$_SERVER['PHP_AUTH_USER'] = $name;
$_SERVER['PHP_AUTH_PW'] = $password;
}

$AUTHENTICATED = 0;
if (ADMIN_PASSWORD!='password' && ($MYREQUEST['LO'] == 1 || isset($_SERVER['PHP_AUTH_USER']))) {