Using Google IAM for GKE service web access
Okay, I managed to make it work perfectly. But it took a few steps. I am including the manifest here that is required to setup the IAP using an ingress. It requires a few things which I listed in the manifest below. Hopefully this can help others since I could not find a single source that had all of this put together. Essentially all you need to do is run kubectl apply -f secure-ingress.yaml to make everything work (as long as you have all the depenedencies) and then you just need to configure your IAP as you like it.



secure-ingress.yaml

# Configure IAP security using ingress automatically
# requirements: kubernetes version at least 1.10.5-gke.3
# requirements: service must respond with 200 at / endpoint (the healthcheck)
# dependencies: need certificate secret my-secret-cert
# dependencies: need oath-client secret my-secret-oath (with my.domain.com configured)
# dependencies: need external IP address my-external-ip
# dependencies: need domain my.domain.com to point to my-external-ip IP
# dependencies: need an app (deployment/statefulset) my-app
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: my-secure-ingress
  namespace: default
  annotations:
    kubernetes.io/ingress.class: "gce"
    kubernetes.io/ingress.allow-http: "false"
    kubernetes.io/ingress.global-static-ip-name: my-external-ip
spec:
  tls:
  - secretName: my-secret-cert
  backend:
    serviceName: my-service-be-web
    servicePort: 1234
---
kind: Service
apiVersion: v1
metadata:
  name: my-service-be-web
  namespace: default
  annotations:
    beta.cloud.google.com/backend-config:
      '{"default": "my-service-be-conf"}'
spec:
  type: NodePort
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 1234
      targetPort: 1234
      name: my-port-web
---
apiVersion: cloud.google.com/v1beta1
kind: BackendConfig
metadata:
  name: my-service-be-conf
  namespace: default
spec:
  iap:
    enabled: true
    oauthclientCredentials:
      secretName: my-secret-oath