gateway-api: requestHeaderModifier in HTTPRoute cannot set Host header

[nak3]

Bug description

Affected product area (please put an X in all that apply)

[X] Networking

Expected behavior

• When requestHeaderModifier sets Host header and controller should add the header via different directive.
• :authority also cannot be set with the same reason.

Steps to reproduce the bug

1. Try to set Host: foo.example.com in HTTPRoute

cat <<EOF | kubectl apply -f -
apiVersion: networking.x-k8s.io/v1alpha1
kind: HTTPRoute
metadata:
  name: host-header
spec:
  gateways:
    allow: FromList
    gatewayRefs:
    - name: test-gateway
      namespace: knative-serving
  hostnames:
  - test.example.com
  rules:
  - filters:
    - requestHeaderModifier:
        set:
          Host: foo.example.com
      type: RequestHeaderModifier
    forwardTo:
    - port: 80
      serviceName: ingress-conformance-host-rewrite-njaysumq
      weight: 1
    matches:
    - path:
        type: Prefix
        value: /
EOF

2. istio-ingressgateway rejects the HTTPRoute

$ kubectl  -n istio-system logs istio-ingressgateway-d5dfc5d8b-cl8bg -f
  ...
2021-04-01T06:25:15.732110Z	warning	envoy config	gRPC config for type.googleapis.com/envoy.config.route.v3.RouteConfiguration rejected: :-prefixed or host headers may not be modified

$ kubectl  -n istio-system  logs istiod-85f9ccb96d-ks8hd |grep -i header
2021-04-01T05:33:04.824343Z	warn	ads	ADS:RDS: ACK ERROR router~172.20.37.2~istio-ingressgateway-d5dfc5d8b-vms5m.istio-system~istio-system.svc.cluster.local-1 Internal::-prefixed or host headers may not be modified

Version

$ istioctl version
client version: 1.10-alpha.75974d56a327e9857f36d17151b2ef3146745b92
control plane version: 1.10-alpha.75974d56a327e9857f36d17151b2ef3146745b92
data plane version: 1.10-alpha.75974d56a327e9857f36d17151b2ef3146745b92 (2 proxies)

[howardjohn]

This is broken in VirtualService as well it seems...