The rlm_chap module provides CHAP functionality.
This module validates a user with CHAP authentication.
If called in Authorize, it will look for CHAP-Password
attribute in the Acess-Request and adds an Auth-Type
attribute set to CHAP if the Config-Items list unless
Auth-Type has already set.
CHAP authentication requires access to the clear-text
password for the user. Standard Unix system authentication
or passwords encrypted via crypt() are not compatible