You can download latest Pear Auth files here
http://pear.php.net/package/Auth/
Auth 1.6.2 (stable) was released on 2009-10-15
I suggest you make your own 'pear directory' in your webroot
and add what pear classes you need as subfolders
to this /pear/ directory
Then whenever you need you can include those classes
in your webscripts