Add authz library (#8002)

* Add function to get EventPolicies of resource

* Switch from kmeta.Accessor to GVK and ObjectMeta as reconcilers don't provision TypeMeta field on resouces

* Add function comment

* WIP Add ResolveSubjects function

* Switch to authenticatable resolver

* Add more unit tests for ResolveSubjects

* Switch to strings.EqualFold for ref comparing

* Add SubjectContained method to check if subject is contained in list of allowed subjects

* Add missing boilerplate

* Run goimports and gofmt

* Use label selectors

* Move check for empty .spec.to at top

* Remove unneeded code

* Ignore references APIVersion version part, when listing EPs for a resource

* Switch to native GroupVersion parsing functions

* Remove unneeded strings.ToLower()

pkg/auth/event_policy.go

@@ -0,0 +1,147 @@
+/*
+Copyright 2024 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+	http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package auth
+
+import (
+	"fmt"
+	"strings"
+
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/labels"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"knative.dev/eventing/pkg/apis/eventing/v1alpha1"
+	listerseventingv1alpha1 "knative.dev/eventing/pkg/client/listers/eventing/v1alpha1"
+	"knative.dev/pkg/resolver"
+)
+
+// GetEventPoliciesForResource returns the applying EventPolicies for a given resource
+func GetEventPoliciesForResource(lister listerseventingv1alpha1.EventPolicyLister, resourceGVK schema.GroupVersionKind, resourceObjectMeta metav1.ObjectMeta) ([]*v1alpha1.EventPolicy, error) {
+	policies, err := lister.EventPolicies(resourceObjectMeta.GetNamespace()).List(labels.Everything())
+	if err != nil {
+		return nil, fmt.Errorf("failed to list eventpolicies: %w", err)
+	}
+
+	relevantPolicies := []*v1alpha1.EventPolicy{}
+
+	for _, policy := range policies {
+		if len(policy.Spec.To) == 0 {
+			// policy applies to all resources in namespace
+			relevantPolicies = append(relevantPolicies, policy)
+		}
+
+		for _, to := range policy.Spec.To {
+			if to.Ref != nil {
+				refGV, err := schema.ParseGroupVersion(to.Ref.APIVersion)
+				if err != nil {
+					return nil, fmt.Errorf("cannot split apiVersion into group and version: %s", to.Ref.APIVersion)
+				}
+
+				if strings.EqualFold(to.Ref.Name, resourceObjectMeta.GetName()) &&
+					strings.EqualFold(refGV.Group, resourceGVK.Group) &&
+					strings.EqualFold(to.Ref.Kind, resourceGVK.Kind) {
+
+					relevantPolicies = append(relevantPolicies, policy)
+					break // no need to check the other .spec.to's from this policy
+				}
+			}
+
+			if to.Selector != nil {
+				selectorGV, err := schema.ParseGroupVersion(to.Selector.APIVersion)
+				if err != nil {
+					return nil, fmt.Errorf("cannot split apiVersion into group and version: %s", to.Selector.APIVersion)
+				}
+
+				if strings.EqualFold(selectorGV.Group, resourceGVK.Group) &&
+					strings.EqualFold(to.Selector.Kind, resourceGVK.Kind) {
+
+					selector, err := metav1.LabelSelectorAsSelector(to.Selector.LabelSelector)
+					if err != nil {
+						return nil, fmt.Errorf("failed to parse selector: %w", err)
+					}
+
+					if selector.Matches(labels.Set(resourceObjectMeta.Labels)) {
+						relevantPolicies = append(relevantPolicies, policy)
+						break // no need to check the other .spec.to's from this policy
+					}
+				}
+			}
+		}
+	}
+
+	return relevantPolicies, nil
+}
+
+// ResolveSubjects returns the OIDC service accounts names for the objects referenced in the EventPolicySpecFrom.
+func ResolveSubjects(resolver *resolver.AuthenticatableResolver, eventPolicy *v1alpha1.EventPolicy) ([]string, error) {
+	allSAs := []string{}
+	for _, from := range eventPolicy.Spec.From {
+		if from.Ref != nil {
+			sas, err := resolveSubjectsFromReference(resolver, *from.Ref, eventPolicy)
+			if err != nil {
+				return nil, fmt.Errorf("could not resolve subjects from reference: %w", err)
+			}
+			allSAs = append(allSAs, sas...)
+		} else if from.Sub != nil {
+			allSAs = append(allSAs, *from.Sub)
+		}
+	}
+
+	return allSAs, nil
+}
+
+func resolveSubjectsFromReference(resolver *resolver.AuthenticatableResolver, reference v1alpha1.EventPolicyFromReference, trackingEventPolicy *v1alpha1.EventPolicy) ([]string, error) {
+	authStatus, err := resolver.AuthStatusFromObjectReference(&corev1.ObjectReference{
+		APIVersion: reference.APIVersion,
+		Kind:       reference.Kind,
+		Namespace:  reference.Namespace,
+		Name:       reference.Name,
+	}, trackingEventPolicy)
+
+	if err != nil {
+		return nil, fmt.Errorf("could not resolve auth status: %w", err)
+	}
+
+	objSAs := authStatus.ServiceAccountNames
+	if authStatus.ServiceAccountName != nil {
+		objSAs = append(objSAs, *authStatus.ServiceAccountName)
+	}
+
+	objFullSANames := make([]string, 0, len(objSAs))
+	for _, sa := range objSAs {
+		objFullSANames = append(objFullSANames, fmt.Sprintf("system:serviceaccount:%s:%s", reference.Namespace, sa))
+	}
+
+	return objFullSANames, nil
+}
+
+// SubjectContained checks if the given sub is contained in the list of allowedSubs
+// or if it matches a prefix pattern in subs (e.g. system:serviceaccounts:my-ns:*)
+func SubjectContained(sub string, allowedSubs []string) bool {
+	for _, s := range allowedSubs {
+		if strings.EqualFold(s, sub) {
+			return true
+		}
+
+		if strings.HasSuffix(s, "*") &&
+			strings.HasPrefix(sub, strings.TrimSuffix(s, "*")) {
+			return true
+		}
+	}
+
+	return false
+}