According to folks on their forum, there's another step to lock down:
https://community.libretranslate.com/t/locking-down-api-key-on-self-hosted-through-cloudron/1767/2
We may need to update the docs here on cloudron:
To configure requirement for api key to use, set --req-limit to 0 and add the --api-keys flag. Requests made without a proper api key will be rejected.