OpenVPN PAM authentication not working

[alefello]

I've a VPN server with Debian 11 and OpenVPN where PAM authentication works only if I start OpenVPN server manually from root account. If I leave it start automatically from system services (I think is systemd this way) the VPN server starts but authentication from client always fails. The client behavior in this case is weird, it doesn't say authentication failed or wrong password or other, but it continues to write a message about "timeout" or "waiting" (I don't remember, I've to check again) but anyway it doesn't bring VPN up.
I already checked the systemd configuration and CAP_AUDIT_WRITE is already there.
What else could it be the problem?

[cron2]

What PAM modules are you trying to use? Stuff like /etc/passwd might not be accessible due to systemd protecting things.

Anything interesting interesting in the OpenVPN log (--verb 3 or 4, please)?

@dsommers, @flichtenheld any ideas in which way systemd might get in the way here?

[cron2]

@alefello if you are not talking to me, there is nothing we can do for you.