Redirect oauth2 proxy to custom page in case of 500 server error - kubernetes

Question

I would like to either be able to customise the existing 500 error page OR in case it is not possible, redirect to my custom page.
I am using Okta oidc and everything is setup on Kubernetes cluster. I could not find where I can configure this 500 server error page.
Below is my POC for a somewhat similar setup but this is using github provider.
apiVersion: apps/v1
kind: Deployment
metadata:
name: demo
spec:
selector:
matchLabels:
app: demo
replicas: 1
template:
metadata:
labels:
app: demo
version: new
spec:
containers:
- name: nginx
image: nikk007/nginxwebsite
---
apiVersion: v1
kind: Service
metadata:
name: myservice
spec:
selector:
app: demo
ports:
- name: http
port: 80
nodePort: 30080
type: NodePort
---
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
name: ingress-gateway-configuration
spec:
selector:
istio: ingressgateway # use Istio default gateway implementation
servers:
- port:
number: 443
name: https
protocol: HTTPS
tls:
mode: SIMPLE
credentialName: selfsigned-cert-tls-secret
hosts:
- "*" # Domain name of the external website
---
apiVersion: cert-manager.io/v1
kind: Issuer
metadata:
name: test-selfsigned
namespace: istio-system
spec:
selfSigned: {}
---
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
name: selfsigned-cert
namespace: istio-system
spec:
dnsNames:
- mymy.com
secretName: selfsigned-cert-tls-secret
issuerRef:
name: test-selfsigned
---
kind: VirtualService
apiVersion: networking.istio.io/v1alpha3
metadata:
name: myvs # "just" a name for this virtualservice
namespace: default
spec:
hosts:
- "*" # The Service DNS (ie the regular K8S Service) name that we're applying routing rules to.
gateways:
- ingress-gateway-configuration
http:
- route:
- destination:
host: oauth2-proxy # The Target DNS name
port:
number: 4180
---
kind: DestinationRule # Defining which pods should be part of each subset
apiVersion: networking.istio.io/v1alpha3
metadata:
name: grouping-rules-for-our-photograph-canary-release # This can be anything you like.
namespace: default
spec:
host: myservice.default.svc.cluster.local # Service
subsets:
- labels: # SELECTOR.
version: new # find pods with label "safe"
name: new-group
- labels:
version: old
name: old-group
---
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: oauth2-proxy
name: oauth2-proxy
spec:
replicas: 1
selector:
matchLabels:
app: oauth2-proxy
template:
metadata:
labels:
app: oauth2-proxy
spec:
containers:
- args:
- --provider=github
- --email-domain=*
- --upstream=file:///dev/null
- --http-address=0.0.0.0:4180
# Register a new application
# https://github.com/settings/applications/new
env:
- name: OAUTH2_PROXY_CLIENT_ID
value: <myapp-client-id>
- name: OAUTH2_PROXY_CLIENT_SECRET
value: <my-app-secret>
- name: OAUTH2_PROXY_COOKIE_SECRET
value: <cookie-secret-I-generated-via-python>
image: quay.io/oauth2-proxy/oauth2-proxy:latest
imagePullPolicy: Always
name: oauth2-proxy
ports:
- containerPort: 4180
protocol: TCP
---
apiVersion: v1
kind: Service
metadata:
labels:
app: oauth2-proxy
name: oauth2-proxy
spec:
ports:
- name: http
port: 4180
protocol: TCP
targetPort: 4180
selector:
app: oauth2-proxy
I am using cert-manager for self signed certificates.
I am using istio ingress gateway instead of k8s ingress controller.
Everything is working fine and I am able to access istio gateway, which directs to oauth2-proxy page, which directs to github login.
In case there is issue with authorization provider, then we get an error 500 page via outh2-proxy. I want to configure oauth2-proxy to redirect to my custom page(or i would like to configure the oauth2-proxy internal html for error page) in case of 500 error. I tried kubectl exec into oauth2-proxy pod but I could not locate their html. Moreover, I dont have root access inside oauth2-proxy pod.
If my own app throws 500 error then I can handle it by configuring its nginx.