[RFC-0010] Add multi-tenant workload identity support for Azure GitRepository

Signed-off-by: Dipti Pai <diptipai89@outlook.com>

Author: dipti-pai

api/v1/gitrepository_types.go

@@ -98,6 +98,11 @@ type GitRepositorySpec struct {
 	// +optional
 	Provider string `json:"provider,omitempty"`
 
+	// ServiceAccountName is the name of the Kubernetes ServiceAccount used to
+	// authenticate to the GitRepository. This field is only supported for 'azure' provider.
+	// +optional
+	ServiceAccountName string `json:"serviceAccountName,omitempty"`
+
 	// Interval at which the GitRepository URL is checked for updates.
 	// This interval is approximate and may be subject to jitter to ensure
 	// efficient use of resources.

config/crd/bases/source.toolkit.fluxcd.io_gitrepositories.yaml

@@ -174,6 +174,11 @@ spec:
                 required:
                 - name
                 type: object
+              serviceAccountName:
+                description: |-
+                  ServiceAccountName is the name of the Kubernetes ServiceAccount used to
+                  authenticate to the GitRepository. This field is only supported for 'azure' provider.
+                type: string
               sparseCheckout:
                 description: |-
                   SparseCheckout specifies a list of directories to checkout when cloning

docs/api/v1/source.md

@@ -412,6 +412,19 @@ When not specified, defaults to &lsquo;generic&rsquo;.</p>
 </tr>
 <tr>
 <td>
+<code>serviceAccountName</code><br>
+<em>
+string
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>ServiceAccountName is the name of the Kubernetes ServiceAccount used to
+authenticate to the GitRepository. This field is only supported for &lsquo;azure&rsquo; provider.</p>
+</td>
+</tr>
+<tr>
+<td>
 <code>interval</code><br>
 <em>
 <a href="https://pkg.go.dev/k8s.io/apimachinery/pkg/apis/meta/v1#Duration">
@@ -2065,6 +2078,19 @@ When not specified, defaults to &lsquo;generic&rsquo;.</p>
 </tr>
 <tr>
 <td>
+<code>serviceAccountName</code><br>
+<em>
+string
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>ServiceAccountName is the name of the Kubernetes ServiceAccount used to
+authenticate to the GitRepository. This field is only supported for &lsquo;azure&rsquo; provider.</p>
+</td>
+</tr>
+<tr>
+<td>
 <code>interval</code><br>
 <em>
 <a href="https://pkg.go.dev/k8s.io/apimachinery/pkg/apis/meta/v1#Duration">

docs/spec/v1/gitrepositories.md

@@ -393,6 +393,23 @@ flux create secret githubapp ghapp-secret \
     --app-private-key=~/private-key.pem    
 ```
 
+### Service Account reference
+
+`.spec.serviceAccountName` is an optional field to specify a Service Account
+in the same namespace as GitRepository with purpose depending on the value of
+the `.spec.provider` field:
+
+- When `.spec.provider` is set to `azure`, the Service Account
+  will be used for Workload Identity authentication. In this case, the controller
+  feature gate `ObjectLevelWorkloadIdentity` must be enabled, otherwise the
+  controller will error out.
+
+**Note:** that for a publicly accessible git repository, you don't need to
+provide a `secretRef` nor `serviceAccountName`.
+
+For a complete guide on how to set up authentication for cloud providers,
+see the integration [docs](/flux/integrations/).
+
 ### Interval
 
 `.spec.interval` is a required field that specifies the interval at which the

internal/controller/gitrepository_controller.go

@@ -663,6 +663,21 @@ func (r *GitRepositoryReconciler) getAuthOpts(ctx context.Context, obj *sourcev1
 		getCreds = func() (*authutils.GitCredentials, error) {
 			var opts []auth.Option
 
+			if obj.Spec.ServiceAccountName != "" {
+				// Check object-level workload identity feature gate.
+				if !auth.IsObjectLevelWorkloadIdentityEnabled() {
+					const gate = auth.FeatureGateObjectLevelWorkloadIdentity
+					const msgFmt = "to use spec.serviceAccountName for provider authentication please enable the %s feature gate in the controller"
+					err := serror.NewStalling(fmt.Errorf(msgFmt, gate), meta.FeatureGateDisabledReason)
+					conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, meta.FeatureGateDisabledReason, "%s", err)
+					return nil, err
+				}
+				serviceAccount := client.ObjectKey{
+					Name:      obj.Spec.ServiceAccountName,
+					Namespace: obj.GetNamespace(),
+				}
+				opts = append(opts, auth.WithServiceAccount(serviceAccount, r.Client))
+			}
 			if r.TokenCache != nil {
 				involvedObject := cache.InvolvedObject{
 					Kind:      sourcev1.GitRepositoryKind,
@@ -742,6 +757,14 @@ func (r *GitRepositoryReconciler) getAuthOpts(ctx context.Context, obj *sourcev1
 	if getCreds != nil {
 		creds, err := getCreds()
 		if err != nil {
+			// Check if it's already a structured error and preserve it
+			if se, ok := err.(*serror.Stalling); ok {
+				return nil, se
+			}
+			if ge, ok := err.(*serror.Generic); ok {
+				return nil, ge
+			}
+
 			e := serror.NewGeneric(
 				fmt.Errorf("failed to configure authentication options: %w", err),
 				sourcev1.AuthenticationFailedReason,

internal/controller/gitrepository_controller_test.go

@@ -48,6 +48,7 @@ import (
 
 	kstatus "github.com/fluxcd/cli-utils/pkg/kstatus/status"
 	"github.com/fluxcd/pkg/apis/meta"
+	"github.com/fluxcd/pkg/auth"
 	"github.com/fluxcd/pkg/git"
 	"github.com/fluxcd/pkg/git/github"
 	"github.com/fluxcd/pkg/gittestserver"
@@ -919,6 +920,15 @@ func TestGitRepositoryReconciler_getAuthOpts_provider(t *testing.T) {
 			},
 			wantErr: "ManagedIdentityCredential",
 		},
+		{
+			name: "azure provider with service account and feature gate for object-level identity disabled",
+			url:  "https://dev.azure.com/foo/bar/_git/baz",
+			beforeFunc: func(obj *sourcev1.GitRepository) {
+				obj.Spec.Provider = sourcev1.GitProviderAzure
+				obj.Spec.ServiceAccountName = "azure-sa"
+			},
+			wantErr: auth.FeatureGateObjectLevelWorkloadIdentity,
+		},
 		{
 			name: "github provider with no secret ref",
 			url:  "https://github.com/org/repo.git",