[schoen]

We briefly describe this history on page 6 of

https://jhalderm.com/pub/papers/letsencrypt-ccs19.pdf

in case anyone is more interested (there are also references there for further details). Twice, methods that seemed plausible for proving control over domain names turned out to make assumptions that were potentially violated by shared hosting environments.

Jacques, I'm really sorry for the hassle that these changes caused you.

[tialaramex]

Thanks for the link Seth. I wasn't aware this existed and it's sometimes nice to have something specific to cite as well as convenient that it's all in one place like this.

Edited to add: Wow the Sankey diagram (showing changes in which CA if any is used by a site) is something I hadn't seen anywhere else and is especially useful. Thanks again.