Installing fossil on 9front is not really difficult. Fossil is just a userland server which probably can even be copied as a binary, as long as the cpu is the same.
Here are the hostowner factotum/ctl readout from the auth server:
key proto=p9sk1 user=bootes dom=fritz.box !password?
key proto=dp9ik user=bootes dom=fritz.box !password?
and from the plan9port fossil server (which doesn't know dp9ik):
key dom=fritz.box proto=p9sk1 user=bootes !password?
I installed the standard /lib/ndb/auth:
hostid=bootes
uid=!sys uid=!adm uid=*
Though, Moody's advice to try disabling auth in the fossil server using the fossilcons may be a far simpler solution.