I spent a while trying to come up with a way to update my dynamic DNS entries at easyDNS from opnsense. Sadly the os-ddclient doesn't have native support for easyDNS. Their is however a custom option under service that allows you select "custom GET" for the protocol. For the server you enter this URL: https://api.cp.easydns.com/dyn/generic.php?hostname=example.com. Modify example.com as appropriate. You have to put the same domain name that's in the the previous URL in the Hostname field. Actually I suspect you can put anything in the hostname field as it doesn't seems to have an impact. The Wildcard box should not be checked, as I don't think it would update the URL correctly. I checked the Force SSL field, as the easyDNS site indicate SSL was required. And lastly you need to generate a "DYN Authentication Token" on dynamic records page, off the DNS Setting page from your easyDNS account. This value is used for the password field. No log entries are generated, but in my test my IP address was updated.