How to access keycloak metrics and healthcheck endpoints ?

Issue

Calling the health endpoint delivers over HTTP no content

curl -v http://localhost:9000/health
*   Trying ::1:9000...
* Connected to localhost (::1) port 9000 (#0)
> GET /health HTTP/1.1
> Host: localhost:9000
> User-Agent: curl/7.76.1
> Accept: */*
> 
* Empty reply from server
* Closing connection 0
curl: (52) Empty reply from server

with the following keycloak configuration settings:

Current Mode: production
Current Configuration:
    kc.health-enabled =  true (keycloak.conf)
    kc.cache-stack =  jdbc-ping (keycloak.conf)
       ....