Create a k8schain directly from pull secrets (#1049)

* Create a k8schain directly from pull secrets

The k8schain package creates a new keychain by resolving Kubernets
secrets from service accounts and other image pull secrets specified by
name. The k8s client gets the full secret content for these named
resources.

Sometimes it's desirable to pull the content of a secret from a cache,
or to watch a resource for changes in a controller. In this situation
it would be helpful to create a k8schain directly from resolved secrets,
without making calls to the k8s api server.

This change refactors the existing k8schain.New() method to separate the
resolution of secrets from the creation of the keychain. This is only a
refactoring of existing behavior to shortcut the k8s api lookups. There
is no change in existing behavior for the keychain.

Added:

    k8schain.NewFromPullSecrets(context.Context, []corev1.Secret) (authn.Keychain, error)

Signed-off-by: Scott Andrews <andrewssc@vmware.com>

* gofmt

Signed-off-by: Scott Andrews <andrewssc@vmware.com>

pkg/authn/k8schain/k8schain.go

@@ -23,7 +23,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/name"
 	credentialprovider "github.com/vdemeester/k8s-pkg-credentialprovider"
 	credentialprovidersecrets "github.com/vdemeester/k8s-pkg-credentialprovider/secrets"
-	v1 "k8s.io/api/core/v1"
+	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/rest"
@@ -66,7 +66,7 @@ func New(ctx context.Context, client kubernetes.Interface, opt Options) (authn.K
 	//    Pod's service account.
 
 	// First, fetch all of the explicitly declared pull secrets
-	var pullSecrets []v1.Secret
+	var pullSecrets []corev1.Secret
 	if client != nil {
 		for _, name := range opt.ImagePullSecrets {
 			ps, err := client.CoreV1().Secrets(opt.Namespace).Get(ctx, name, metav1.GetOptions{})
@@ -90,18 +90,7 @@ func New(ctx context.Context, client kubernetes.Interface, opt Options) (authn.K
 		}
 	}
 
-	once.Do(func() {
-		keyring = credentialprovider.NewDockerKeyring()
-	})
-
-	// Third, extend the default keyring with the pull secrets.
-	kr, err := credentialprovidersecrets.MakeDockerKeyring(pullSecrets, keyring)
-	if err != nil {
-		return nil, err
-	}
-	return &keychain{
-		keyring: kr,
-	}, nil
+	return NewFromPullSecrets(ctx, pullSecrets)
 }
 
 // NewInCluster returns a new authn.Keychain suitable for resolving image references as
@@ -132,6 +121,23 @@ func NewNoClient(ctx context.Context) (authn.Keychain, error) {
 	return New(ctx, nil, Options{})
 }
 
+// NewFromPullSecrets returns a new authn.Keychain suitable for resolving image references as
+// scoped by the pull secrets.
+func NewFromPullSecrets(ctx context.Context, pullSecrets []corev1.Secret) (authn.Keychain, error) {
+	once.Do(func() {
+		keyring = credentialprovider.NewDockerKeyring()
+	})
+
+	// Extend the default keyring with the pull secrets.
+	kr, err := credentialprovidersecrets.MakeDockerKeyring(pullSecrets, keyring)
+	if err != nil {
+		return nil, err
+	}
+	return &keychain{
+		keyring: kr,
+	}, nil
+}
+
 type lazyProvider struct {
 	kc    *keychain
 	image string

pkg/authn/k8schain/k8schain_test.go

@@ -178,3 +178,68 @@ func TestImagePullSecrets(t *testing.T) {
 		})
 	}
 }
+
+func TestFromPullSecrets(t *testing.T) {
+	username, password := "foo", "bar"
+	specificUser, specificPass := "very", "specific"
+
+	pullSecrets := []corev1.Secret{
+		{
+			ObjectMeta: metav1.ObjectMeta{
+				Name:      "secret",
+				Namespace: "ns",
+			},
+			Type: corev1.SecretTypeDockercfg,
+			Data: map[string][]byte{
+				corev1.DockerConfigKey: []byte(
+					fmt.Sprintf(`{"fake.registry.io": {"auth": %q}, "fake.registry.io/more/specific": {"auth": %q}}`,
+						base64.StdEncoding.EncodeToString([]byte(username+":"+password)),
+						base64.StdEncoding.EncodeToString([]byte(specificUser+":"+specificPass))),
+				),
+			},
+		},
+	}
+
+	kc, err := NewFromPullSecrets(context.Background(), pullSecrets)
+	if err != nil {
+		t.Fatalf("NewFromPullSecrets() = %v", err)
+	}
+
+	repo, err := name.NewRepository("fake.registry.io/more/specific", name.WeakValidation)
+	if err != nil {
+		t.Errorf("NewRegistry() = %v", err)
+	}
+
+	for _, tc := range []struct {
+		name   string
+		auth   authn.Authenticator
+		target authn.Resource
+	}{{
+		name:   "registry",
+		auth:   &authn.Basic{Username: username, Password: password},
+		target: repo.Registry,
+	}, {
+		name:   "repo",
+		auth:   &authn.Basic{Username: specificUser, Password: specificPass},
+		target: repo,
+	}} {
+		t.Run(tc.name, func(t *testing.T) {
+			tc := tc
+			auth, err := kc.Resolve(tc.target)
+			if err != nil {
+				t.Errorf("Resolve(%v) = %v", tc.target, err)
+			}
+			got, err := auth.Authorization()
+			if err != nil {
+				t.Errorf("Authorization() = %v", err)
+			}
+			want, err := tc.auth.Authorization()
+			if err != nil {
+				t.Errorf("Authorization() = %v", err)
+			}
+			if !reflect.DeepEqual(got, want) {
+				t.Errorf("Resolve() = %v, want %v", got, want)
+			}
+		})
+	}
+}