After a brief exchange via email, one of the developers of OPNsense has contributed a modification that will allow for an option to authenticate using credentials for downloading blacklists, something which is essential for Squidblacklist.org members to use and update blacklists with OPNsense. This change will be available in the upcoming 16.7.7 release of OPNsense.
In the coming days and weeks further testing and collaboration should follow, to ensure full functionality, such as automated updates with scheduling options and features. And standard testing for any issues that may arise, but we are very excited to see progress being made. And would like to express our gratitude to the developers who are donating their time and effort to make the world a better place for the end user.
I will post a full review once final testing has concluded and the resultant product is solid, we will also update our materials to reflect the latest changes when we reach this point and confirmation compatibility and stability are achieved.