Describe the bug (This is potentially also a feature request)
We have previously created a ComputeBackendService using Deployment Manager (DM), and then manually turned on Identity-Aware Proxy (IAP), which autogenerates the OAuth2.0 Client ID/secret and attaches it to the ComputeBackendService. We're migrating our GLB resources from DM to KCC, so when the new definition was applied and shows UpToDate, we expected spec.iap to default to the existing GCP configuration. However, 7046 the actual behaviour was that because we left spec.iap empty, it defaulted to not populating spec.iap and turned IAP off for the ComputeBackendService leading to downtime. And with the k8s reconciliation loop, manually turning it on gets corrected automatically again.

As a workaround, we went into GCP console page for API Services & Credentials / OAuth 2.0 Client IDs. Copied the ClientID/secret which was generated when we manually flipped the IAP slider to ON. And then added them to spec.iap, and re-applied which works. Using our Infra-as-Code workflow, this now requires: PR1 to create the ComputeBackendService, manually flip IAP on to create OAuth2.0 clientId/secret, PR2 to add spec.iap.

Alternatively, we could have workflow to: pre-create the OAuth2.0 ClientID (assuming there's no special magic behind the scenes that binds IAP created ClientIDs to these IAP-<service-name> IDs), and PR1 create the full ComputeBackendService with spec.iap. This would be a CRD feature request if we cannot simply have spec.iap: true that does the ClientID generation and binding for us.

In order of awesomeness, the fix would be:

1. spec.iap: true magic that creates Client and binding like the UI experience
2. CRD for OAuth2.0 Client to pre-create and reference in spec.iap.oauth2ClientRef
3. Acquire from GCP and not default to OFF

ConfigConnector Version
1.26.0

YAML snippets:

apiVersion: compute.cnrm.cloud.google.com/v1beta1
kind: ComputeBackendService
metadata:
  name: glb-gke-service--site-reagent
spec:
  iap:  # Had to be added for it to work!
    oauth2ClientId: <REDACTED>.apps.googleusercontent.com
    oauth2ClientSecret:
      valueFrom:
        secretKeyRef:
          key: glb-gke-service--site-reagent
          name: iap-client-secrets
  backend:
  - balancingMode: RATE
    maxRatePerEndpoint: 5
    group:
      networkEndpointGroupRef:
        external: projects/b6i-stg/zones/us-east4-a/networkEndpointGroups/<REDACTED>
  - balancingMode: RATE
    maxRatePerEndpoint: 5
    group:
      networkEndpointGroupRef:
        external: projects/b6i-stg/zones/us-east4-b/networkEndpointGroups/<REDACTED>
  - balancingMode: RATE
    maxRatePerEndpoint: 5
    group:
      networkEndpointGroupRef:
        external: projects/b6i-stg/zones/us-east4-c/networkEndpointGroups/<REDACTED>