Specifies the type(s) of authentication, if any, to be negotiated with
the peer:
none No authentication is negotiated.
pap PAP negotiation only.
chap CHAP negotiation only.
papChap PAP negotiation is attempted first; if fails, attempt CHAP.
chapPap CHAP negotiation is attempted first; if fails, attempt PAP.
Setting this object to none will set
usdPppProfileAuthenticatorVirtualRouter object to an empty string.