PHP_AUTH_USER and filter_input

Starting from PHP 5.2 it is strongly recommend to use filter_input instead of direct $_SERVER, $_GET, etc... but

This method works well for almost all variables, eg.:

filter_input(INPUT_SERVER, 'CONTENT_TYPE', FILTER_SANITIZE_SPECIAL_CHARS);

is near to

filter_var($_SERVER['CONTENT_TYPE']);

but it is unable to retrieve like this PHP_AUTH_USER and PHP_AUTH_PW from $_SERVER superglobal. Below line won't work:

filter_input(INPUT_SERVER, 'PHP_AUTH_USER', FILTER_SANITIZE_SPECIAL_CHARS);

and this one does:

filter_var($_SERVER['PHP_AUTH_USER']);