Run pppoe server:

• sudo apt install pppoe
• put pppoe-server-options at /etc/ppp/
• ip link to find the interface to listen on
• sudo pppoe-server -F -I <interface> to run it
• the password should appear at /var/log/pppoe-server-log

pppoe-server-options

require-pap
login
#lcp-echo-interval 10
#lcp-echo-failure 10
show-password
debug
logfile /var/log/pppoe-server-log