The type of authentication used on the point-to-point link as described in RFC 1334. The authentication protocol supports pap(2) (Password Authentication Protocol), chap(3) (Challenge Handshake Authentication Protocol), or both(4). When set to both(4), the link must be successfully authenticated by either CHAP or PAP. The type ms-chap(6) and ms-chapv2(8) are Microsofts proprietary CHAP authentication procedures (using MD4 and DES encryption instead of MD5 encryption algorithm), all(7) includes PAP, CHAP and MS-CHAP.

Another way to authenticate dial-in users is by using RADIUS (remote authentication dial in user service). Users can authenticate themselves either using PAP or CHAP (excluding MS-CHAP). In general the system creates PPP interfaces with this authentication itself, but it's also possible to take advance of the RADIUS dial-in services with pre-configured interfaces. See biboAdmRadiusServer for further details.