pfSense

It is not possible to enable chap authentication via the gui. The service config file is generated with pap authentication only.

mpd5 supports PAP/CHAP/CHAP-MD5/MSCHAPv1/MSCHAPv2 protocols:
http://mpd.sourceforge.net/doc5/mpd20.html#20

pap
PAP style authentication. Note that this style of authentication is insecure, since the password crosses the link in plaintext.

Default disable and accept.

chap
CHAP style authentication. This style of authentication is safer than PAP, because only a hash of the password is passed over the link. Mpd supports MD5 style CHAP and Microsoft style CHAP versions 1 and 2. Mpd will prefer Microsoft CHAP over MD5 CHAP to get encryption keys.

This option is an alias for chap-md5 chap-msv1 chap-msv2

chap-md5
Traditional CHAP MD5 style authentication.

Default disable and accept.

chap-msv1
Microsoft CHAP style authentication.

Default disable and deny.

chap-msv2
Microsoft CHAP style authentication Version 2.

Default disable and accept.

+ EAP