After LCP negotiation is complete, the authentication protocol agreed on during LCP negotiation using LCP option 3 is used to establish the identity and credentials of the PPP peer that is requesting the PPP connection, typically a remote access client (for remote access dial-up or virtual private network [VPN] connections) or a calling router (for router-to-router dial-up or VPN connections). The authentication process is phase 2 of the PPP connection establishment.
Windows Server 2008 and Windows Vista support the following PPP authentication protocols:
Password Authentication Protocol (PAP)
Challenge Handshake Authentication Protocol (CHAP)
Microsoft Challenge Handshake Authentication Protocol version 2 (MS-CHAP v2) ...