unexpected end of JSON input

Hey,

go: 1.17.2
caddy: 2.4.5

```shell
$ xcaddy build v2.4.5 --with github.com/abiosoft/caddy-json-schema
$ ./caddy json-schema -no-cache
json-schema discarding cache for root config.
json-schema fetching https://caddyserver.com/api/docs/config/ ...
json-schema
json-schema discarding cache for apps/exec.
json-schema fetching https://caddyserver.com/api/docs/config/apps/exec ...
json-schema
json-schema discarding cache for apps/supervisor.
json-schema fetching https://caddyserver.com/api/docs/config/apps/supervisor ...
json-schema
json-schema discarding cache for apps/http.
json-schema fetching https://caddyserver.com/api/docs/config/apps/http ...
json-schema
json-schema discarding cache for apps/pki.
json-schema fetching https://caddyserver.com/api/docs/config/apps/pki ...
json-schema
json-schema discarding cache for apps/tls.
json-schema fetching https://caddyserver.com/api/docs/config/apps/tls ...
json-schema
json-schema discarding cache for apps/auth.
json-schema fetching https://caddyserver.com/api/docs/config/apps/auth ...
json-schema
json-schema: unexpected end of JSON input
```

The url `https://caddyserver.com/api/docs/config/apps/auth` response is empty with 502 error code.

Might not be a good idea to use the web server from caddy itself, it's an external services which can always change.
Like in my case it looks like auth is gone?