Acessing an external proxy from the Istio egress gateway - proxy

Question

I'd need to tightly control all traffic to external sites from the applications in the K8S namespace. As the K8S NetworkPolicy objects allow specifying target IP addresses only we'd prefer using Istio to mange the outgoing traffic so that we can use hostnames instead of CIDRs to configure our external services. Furthermore we have an enterprise wide proxy which must be used for all traffic to the internet.
Following https://istio.io/latest/docs/tasks/traffic-management/egress/http-proxy/ we could manage that the sidecar of the pod (with the proper environment variables HTTP_PROXY etc. set) can access the internet via the corporate proxy. This means that the communication POD --> sidecar --> proxy --> external site works. However in this case the Istio egress gateway is bypassed.
What we'd however need is the following communication path: POD --> sidecar --> Istio egress gateway --> proxy --> external site.
Out current setup is the following:
The PODs have the HTTP_PROXY env. variable set to proxy.int.xxx.zz:8080
We have the following yamls applied:
apiVersion: networking.istio.io/v1beta1
kind: ServiceEntry
metadata:
name: proxylb
spec:
hosts:
- proxy.int.xxx.zz
ports:
- number: 8080
name: tcp
protocol: TCP
location: MESH_EXTERNAL
resolution: DNS
---
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
name: cnn
spec:
hosts:
- edition.cnn.com
ports:
- number: 80
name: http-port
protocol: HTTP
- number: 443
name: tls
protocol: TLS
resolution: DNS
---
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
name: orf
spec:
hosts:
- www.orf.at
ports:
- number: 80
name: http-port
protocol: HTTP
- number: 443
name: tls
protocol: TLS
resolution: DNS
---
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
name: istio-egressgateway
spec:
selector:
istio: egressgateway
servers:
- port:
number: 80
name: http
protocol: HTTP
hosts:
- edition.cnn.com
- www.orf.at
- port:
number: 443
name: tls
protocol: TLS
hosts:
- edition.cnn.com
- www.orf.at
tls:
mode: PASSTHROUGH
- port:
number: 8080
name: tcp
protocol: TCP
hosts:
- proxy.int.xxx.zz
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
name: istio-egressgateway
spec:
host: istio-egressgateway.istio-system.svc.cluster.local
subsets:
- name: cnn
- name: orf
- name: proxylb
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
name: direct-cnn-through-egress-gateway
spec:
hosts:
- edition.cnn.com
gateways:
- mesh
- istio-egressgateway
tls:
- match:
- gateways:
- mesh
port: 443
sniHosts:
- edition.cnn.com
route:
- destination:
host: istio-egressgateway.istio-system.svc.cluster.local
subset: cnn
port:
number: 443
- match:
- gateways:
- istio-egressgateway
port: 443
sniHosts:
- edition.cnn.com
route:
- destination:
host: edition.cnn.com
port:
number: 443
weight: 100
http:
- match:
- gateways:
- mesh
port: 80
route:
- destination:
host: istio-egressgateway.istio-system.svc.cluster.local
subset: cnn
port:
number: 80
weight: 100
- match:
- gateways:
- istio-egressgateway
port: 80
route:
- destination:
host: edition.cnn.com
port:
number: 80
weight: 100
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
name: direct-orf-through-egress-gateway
spec:
hosts:
- www.orf.at
gateways:
- mesh
- istio-egressgateway
tls:
- match:
- gateways:
- mesh
port: 443
sniHosts:
- www.orf.at
route:
- destination:
host: istio-egressgateway.istio-system.svc.cluster.local
subset: orf
port:
number: 443
- match:
- gateways:
- istio-egressgateway
port: 443
sniHosts:
- www.orf.at
route:
- destination:
host: www.orf.at
port:
number: 443
weight: 100
http:
- match:
- gateways:
- mesh
port: 80
route:
- destination:
host: istio-egressgateway.istio-system.svc.cluster.local
subset: orf
port:
number: 80
weight: 100
- match:
- gateways:
- istio-egressgateway
port: 80
route:
- destination:
host: www.orf.at
port:
number: 80
weight: 100
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
name: direct-proxylb-through-egress-gateway
spec:
hosts:
- proxy.int.xxx.zz
gateways:
- mesh
- istio-egressgateway
tcp:
- match:
- gateways:
- mesh
port: 8080
route:
- destination:
host: istio-egressgateway.istio-system.svc.cluster.local
subset: proxylb
port:
number: 8080
weight: 100
- match:
- gateways:
- istio-egressgateway
port: 8080
route:
- destination:
host: proxy.int.xxx.zz
port:
number: 8080
weight: 100
---
apiVersion: networking.istio.io/v1alpha3
kind: Sidecar
metadata:
name: trilateral
spec:
egress:
- hosts:
- "./*"
outboundTrafficPolicy:
mode: REGISTRY_ONLY
However when running a curl we get:
curl -k -I https://istio.io
curl: (56) Recv failure: Connection reset by peer
Should this setup work? What is missing?
Thanks a lot in advance for any hint.