Ubiquiti removed keytool (and java) from recent releases of Unifi OS. This moves from keytool to openssl's native pkcs12.
Tested on Unifi Dream Machine which runs Unifi OS and a built-in Unifi controller.
Also added backup of existing files prior to change in case anything goes wrong, and update system configuration with compatible ciphers.
Adding this to at least partially prevent the virtually nonexistent possibility of timestamp and _utc_date() mismatch. If the normal date -u -d does not get converted (looking at you Solaris!), the poor man's method with manipulating the _utc_date() string output kicks in.