FrankenPHP, Caddy as well the Mercure and Vulcain modules can be configured using [the formats supported by Caddy](https://caddyserver.com/docs/getting-started#your-first-config).
In the Docker image, the `Caddyfile` is located at `/etc/Caddyfile`.
You can also configure PHP using `php.ini` as usual.
In the Docker image, the `php.ini` file is located at `/usr/local/lib/php.ini`.