https://strugglers.net/~andy/blog/2018/03/19/\ lets-encrypt-wildcard-certificates-acme-sh-and-automated-dns-verification/
Ironically, the article can be accessed through either http or https. This is the article which let me to the split-horizon solution presented in this paper, and I gratefully acknowledge the information in this paper as being mostly plundered from Andy's article.
When I started this project I began with a web search and landed on the strugglers.net article. I read it with much interest, and then set about getting things working.
Later, when writing this article I looked back at the strugglers.net site again, and was much chagrined to discover that this article is an unintentional paraphrase of Andy's web article. I almost trashed this article altogether, then decided to keep it because it chronicles my project, and its solution in my environment. In that spirit, perhaps someone else will find elucidation in a turn of phrase.
Therefore, thanks Andy, for your useful, complete, and inspiring article. My current effort is merely detail.