Caddyfile

localhost {

  # Define named matchers satisfying a combination of content request specs
  @rdf {
    conneg {
      match_types application/rdf+xml application/x-turtle
      force_type_query_string format
    }
  }

  @rdfFr {
    conneg {
      match_types application/rdf+xml application/x-turtle
      force_type_query_string format
      match_languages fr
      force_language_query_string lang
    }
  }

  @rdfDeEn {
    conneg {
      match_types application/rdf+xml application/x-turtle
      force_type_query_string format
      match_languages de en
      force_language_query_string lang
      var_language lang
    }
  }

  @htmlBrotli {
    conneg {
      match_types text/html
      force_type_query_string format
      match_encodings br brotli
      force_encoding_query_string enc
    }
  }

  @html {
    conneg {
      match_types text/html
      force_type_query_string format
    }
  }

  # Test with the following:

  respond @rdfFr "RDF en français!
"

  respond @rdfDeEn "RDF auf deutsch oder englisch, {vars.conneg_lang} preferred!
"

  respond @rdf "RDF!
"

  respond @htmlBrotli "HTML, but brotli-compressed!
"

  respond @html "HTML
"

  respond "Default
"

  # If it's working, use like so:
  # reverse_proxy @rdf localhost:8080
}