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 Access-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 with CHAP.
Chris Parker, firstname.lastname@example.org