/etc/strongswan.d/ is in libcharon-extra-plugins 5.3.5-1ubuntu3.8.
This file is owned by root:root, with mode 0o755.
..
/etc/strongswan.d/charon/
/etc/strongswan.d/charon/addrblock.conf
/etc/strongswan.d/charon/certexpire.conf
/etc/strongswan.d/charon/dhcp.conf
/etc/strongswan.d/charon/eap-aka-3gpp2.conf
/etc/strongswan.d/charon/eap-aka.conf
/etc/strongswan.d/charon/eap-dynamic.conf
/etc/strongswan.d/charon/eap-gtc.conf
/etc/strongswan.d/charon/eap-identity.conf
/etc/strongswan.d/charon/eap-md5.conf
/etc/strongswan.d/charon/eap-mschapv2.conf
/etc/strongswan.d/charon/eap-peap.conf
/etc/strongswan.d/charon/eap-radius.conf
/etc/strongswan.d/charon/eap-sim-file.conf
/etc/strongswan.d/charon/eap-sim-pcsc.conf
/etc/strongswan.d/charon/eap-sim.conf
/etc/strongswan.d/charon/eap-simaka-pseudonym.conf
/etc/strongswan.d/charon/eap-simaka-reauth.conf
/etc/strongswan.d/charon/eap-simaka-sql.conf
/etc/strongswan.d/charon/eap-tls.conf
/etc/strongswan.d/charon/eap-tnc.conf
/etc/strongswan.d/charon/eap-ttls.conf
/etc/strongswan.d/charon/error-notify.conf
/etc/strongswan.d/charon/farp.conf
/etc/strongswan.d/charon/kernel-libipsec.conf
/etc/strongswan.d/charon/led.conf
/etc/strongswan.d/charon/lookip.conf
/etc/strongswan.d/charon/unity.conf
/etc/strongswan.d/charon/xauth-eap.conf
/etc/strongswan.d/charon/xauth-generic.conf
/etc/strongswan.d/charon/xauth-noauth.conf
/etc/strongswan.d/charon/xauth-pam.conf