set service pppoe-server authentication local-users username test password 'test'
set service pppoe-server authentication mode 'local'
set service pppoe-server client-ipv6-pool delegate-prefix '2001:db8:8003::1/48,56'
set service pppoe-server client-ipv6-pool prefix '2001:db8:8002::1/48,64'
set service pppoe-server dnsv6-servers server-1 '2001:4860:4860::8888'
set service pppoe-server interface 'eth2'
set service pppoe-server local-ip '192.168.96.28'

and debian9 with pppoeconf and wide-dhcp for dhcpv6 and the delegated prefix.