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.
dns_dyn.sh, remove empty line at end
dns_dyn.sh, remove trailing spaces at end of line
Replace 'head -n' with the '_head_n' function
Update main README.md DNS API list
