# This allows completely open access:
AuthorizedKeysCommand=/bin/echo %t %k
# Only this closes it back up:
ForceCommand=/home/u/.ssh/AnonymousAccessCommand

AuthenticationMethods publickey
AuthorizedKeysCommandUser=u
ExposeAuthInfo=yes

Port=22022
HostKey=/home/u/.ssh/id_ed25519
PidFile=/home/u/.ssh/sshd.pid

AcceptEnv LANG LC_*
UsePAM no
PermitTTY no
ChrootDirectory=none