We installing `npppd-users' with uid:gid root:wheel and mode 0600 because it consists sensitive data but mode for npppd.conf is 0640. npppd.conf can also have radius passwords and nothing requires to allow it be readable by group. So set it's permissions to 0600.
Index: usr.sbin/npppd/Makefile =================================================================== RCS file: /cvs/src/usr.sbin/npppd/Makefile,v retrieving revision 1.6 diff -u -p -r1.6 Makefile --- usr.sbin/npppd/Makefile 14 Mar 2013 16:20:46 -0000 1.6 +++ usr.sbin/npppd/Makefile 21 Jun 2020 13:37:50 -0000 @@ -6,7 +6,7 @@ SUBDIR+= npppd distribution: - ${INSTALL} -C -o root -g wheel -m 0640 ${.CURDIR}/npppd/npppd.conf \ + ${INSTALL} -C -o root -g wheel -m 0600 ${.CURDIR}/npppd/npppd.conf \ ${DESTDIR}/etc/npppd/npppd.conf ${INSTALL} -C -o root -g wheel -m 0600 ${.CURDIR}/npppd/npppd-users \ ${DESTDIR}/etc/npppd/npppd-users