I was trying to explain that during my initial browsing of the Caddy site, I found several references to using the API endpoints to configure Caddy, but nothing in the same places to say how to secure it or whether it was enabled by default. I wasn't talking about any sort of cunning attack, simply the issue of having such functionality accessible to anyone who could visit /config/ and knew anything about HTTP.
I did later discover the relevant configuration in the JSON config structure documentation, including the flag to disable it that is what I really wanted to know about. It just seemed like the kind of important detail that would be worth linking from places that introduce the REST API, such as the section about it on your v2 landing page, if you're refining the site.
Keep in mind that if your system runs untrusted code, all bets are off: there's not really anything we can do as a single user space process to protect it. If your system runs untrusted code, you'll need to make sure your system is locked down properly... maybe you can use a permissioned unix socket for the admin endpoint, or just disable it entirely... it's really up to you. I think our defaults are safe though. Let me know if they aren't.