Panic in authorino pod when defining a k8s SAR rule without the user field

[roivaz]

Describe the bug

The authorino process panics when the user field in a k8s SAR authorization rule is not defined.

Help us Reproduce it

1. Create the following Kuadrant AuthPolicy

apiVersion: kuadrant.io/v1beta2
kind: AuthPolicy
metadata:
  name: sar-protected-api
spec:
  targetRef:
    group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: some-route
  routeSelectors:
    - matches:
        - path:
            type: PathPrefix
            value: /some-path
  rules:
    authentication:
      "service-accounts":
        kubernetesTokenReview:
          audiences:
            - "https://example.com"
    authorization:
      "k8s-rbac":
        kubernetesSubjectAccessReview:
          groups:
            - "some-group"

2. Check the logs of the authorino pod to see the following panic

{"level":"info","ts":"2024-10-10T14:30:50Z","logger":"authorino","msg":"Observed a panic in reconciler: runtime error: invalid memory address or nil pointer dereference","controller":"authconfig","controllerGroup":"authorino.kuadrant.io","controllerKind":"AuthConfig","AuthConfig":{"name":"ap-3scale-saas-backend-internal-api","namespace":"3scale-saas"},"namespace":"3scale-saas","name":"ap-3scale-saas-backend-internal-api","reconcileID":"23813405-f48b-4cda-a0f9-ef21c5d6aa8c"}
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1b5cd9c]
goroutine 180 [running]:
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile.func1()
/opt/app-root/src/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.16.3/pkg/internal/controller/controller.go:116 +0x1e5
panic({0x1de0b00?, 0x36d5b30?})
/usr/lib/golang/src/runtime/panic.go:914 +0x21f
github.com/kuadrant/authorino/controllers.(*AuthConfigReconciler).translateAuthConfig(0xc00067e680, {0x25020a8, 0xc000c40db0}, 0xc00027f4a0)
/usr/src/authorino/controllers/auth_config_controller.go:424 +0x1bdc
github.com/kuadrant/authorino/controllers.(*AuthConfigReconciler).Reconcile(0xc00067e680, {0x25020a8, 0xc000afdf80}, {{{0xc0003edaa0?, 0x5?}, {0xc00043ae70?, 0xc000736d08?}}})
/usr/src/authorino/controllers/auth_config_controller.go:114 +0x4ee
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile(0x2507490?, {0x25020a8?, 0xc000afdf80?}, {{{0xc0003edaa0?, 0xb?}, {0xc00043ae70?, 0x0?}}})
/opt/app-root/src/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.16.3/pkg/internal/controller/controller.go:119 +0xb7
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler(0xc0007c14a0, {0x25020e0, 0xc0007b1270}, {0x1ebbba0?, 0xc0000a87a0?})
/opt/app-root/src/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.16.3/pkg/internal/controller/controller.go:316 +0x3cc
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem(0xc0007c14a0, {0x25020e0, 0xc0007b1270})
/opt/app-root/src/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.16.3/pkg/internal/controller/controller.go:266 +0x1af
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2()
/opt/app-root/src/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.16.3/pkg/internal/controller/controller.go:227 +0x79
created by sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2 in goroutine 93
/opt/app-root/src/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.16.3/pkg/internal/controller/controller.go:223 +0x565

Expected behavior

Don't panic and report the error somehow (logs, conditions or even reject the AuthPolicy/AuthConfig).

Environment (please complete the following information):

• Openshift 4.16
• kuadrant v0.11.0 & authorino-operator v0.13.0

Additional context

Slack conversation https://kubernetes.slack.com/archives/C05J0D0V525/p1728554107621359