api: factor out auth logger and use for all API authentication failures

we have information here not available in the access log, especially
if the /api2/extjs formatter is used, which encapsulates errors in a
200 response.

So keep the auth log for now, but extend it use from create ticket
calls to all authentication failures for API calls, this ensures one
can also fail2ban tokens.

Do that logging in a central place, which makes it simple but means
that we do not have the user ID information available to include in
the log.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

debian/postinst

@@ -25,6 +25,9 @@ case "$1" in
 				    sed -i '/^\s\+verify-schedule /d' /etc/proxmox-backup/datastore.cfg || true
 			fi
 		fi
+		if dpkg --compare-versions "$2" 'le' '0.9.5-1'; then
+			chown --quiet backup:backup /var/log/proxmox-backup/api/auth.log || true
+		fi
 	fi
 	# FIXME: Remove in future version once we're sure no broken entries remain in anyone's files
 	if grep -q -e ':termproxy::[^@]\+: ' /var/log/proxmox-backup/tasks/active; then