CHAP Handshake
When the authentication mode is CHAP, the user credentials sent to the RADIUS server include “username,” “CHAP-Password,” and “CHAP-Challenge.” The “CHAP-Password” credential uses MD-5 one way. This is calculated over this series of the following values, in this order: challenge-id (which for the Oracle® Enterprise Session Border Controller is always 0), followed by the user password, and then the challenge (as specified in RFC 1994, section 4.1).