$ curl -i http://localhost:8080/api/echo/hello

First request  -> status 200, ETag "04b614fb02225a0cb24f7520b58e80cb1", body 'echo: hello'

$ curl -i http://localhost:8080/api/echo/hello -H 'If-None-Match: "04b614fb02225a0cb24f7520b58e80cb1"'

Second request -> status 304 (org.springframework.web.filter.ShallowEtagHeaderFilter, package unchanged on Spring
Framework 7.0.9 -- confirmed by compiling against it here, not assumed)
