Really? What if s/he just decrypted the file themselves and had a look at the content, rather than using the convenient wrapper that a password manager provides?
Rule zero of security is that you can't ask people to forget things. If they had knowledge of a shared secret and they're not supposed to going forward, then that shared secret needs to be changed.
The only way this kind of auditing could be trusted is if all the secrets are stored on the server that implements the auditing, which is exactly the model I believe that most users of `pass` are trying to avoid.
There will always be a person with admin (or master password) access who can edit logs or bypass them entirely, but this is suppose to be a person who has the final responsibility in the team's 'chain of command'. The audit log exists so that this very admin can monitor the logs for suspicious behavior and clean up the passwords after a team member leaves. Hence, having the ability to decrypt the db with a master password is irrelevant as the master password should only be accessible to the admin.
