[RFC-0010] Add core auth library

auth/doc.go

@@ -1,5 +1,5 @@
 /*
-Copyright 2024 The Flux authors
+Copyright 2025 The Flux authors
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -14,6 +14,5 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-// Package auth is a Go package for OIDC-based authentication against Git SaaS providers.
-// Includes support for Azure DevOps and GitHub Apps.
+// auth is a package for handling secret-less authentication with cloud providers.
 package auth

auth/get_token.go

@@ -0,0 +1,178 @@
+/*
+Copyright 2025 The Flux 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 (
+	"context"
+	"crypto/sha256"
+	"fmt"
+	"strings"
+
+	authnv1 "k8s.io/api/authentication/v1"
+	corev1 "k8s.io/api/core/v1"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	"github.com/fluxcd/pkg/cache"
+)
+
+// GetToken returns an access token for accessing resources in the given cloud provider.
+func GetToken(ctx context.Context, provider Provider, opts ...Option) (Token, error) {
+
+	var o Options
+	o.Apply(opts...)
+
+	// Initialize default token fetcher.
+	newAccessToken := func() (Token, error) {
+		token, err := provider.NewDefaultToken(ctx, opts...)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create default access token: %w", err)
+		}
+		return token, nil
+	}
+
+	// Initialize service account token fetcher if service account is specified.
+	var providerIdentity string
+	var serviceAccountP *corev1.ServiceAccount
+	if o.ServiceAccount != nil {
+		// Get service account and prepare a function to create a token for it.
+		var serviceAccount corev1.ServiceAccount
+		if err := o.Client.Get(ctx, *o.ServiceAccount, &serviceAccount); err != nil {
+			return nil, fmt.Errorf("failed to get service account: %w", err)
+		}
+		serviceAccountP = &serviceAccount
+
+		// Get provider audience.
+		var err error
+		providerAudience, err := provider.GetAudience(ctx)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get provider audience: %w", err)
+		}
+
+		// Get provider identity.
+		providerIdentity, err = provider.GetIdentity(serviceAccount)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get provider identity from service account '%s/%s' annotations: %w",
+				serviceAccount.Namespace, serviceAccount.Name, err)
+		}
+
+		// Initialize access token fetcher that will use the identity token.
+		newAccessToken = func() (Token, error) {
+			identityToken, err := newServiceAccountToken(ctx, o.Client, serviceAccount, providerAudience)
+			if err != nil {
+				return nil, err
+			}
+
+			token, err := provider.NewTokenForServiceAccount(ctx, identityToken, serviceAccount, opts...)
+			if err != nil {
+				return nil, fmt.Errorf("failed to create access token: %w", err)
+			}
+
+			return token, nil
+		}
+	}
+
+	// Initialize registry token fetcher if artifact repository is specified.
+	newToken := newAccessToken
+	if o.ArtifactRepository != "" {
+		newToken = func() (Token, error) {
+			accessToken, err := newAccessToken()
+			if err != nil {
+				return nil, err
+			}
+
+			token, err := provider.NewArtifactRegistryToken(ctx, o.ArtifactRepository, accessToken, opts...)
+			if err != nil {
+				return nil, fmt.Errorf("failed to create artifact registry login: %w", err)
+			}
+
+			return token, nil
+		}
+	}
+
+	// Bail out early if cache is disabled.
+	if o.Cache == nil {
+		return newToken()
+	}
+
+	// Build cache key.
+	cacheKey := buildCacheKey(provider, providerIdentity, serviceAccountP, opts...)
+
+	// Get involved object details.
+	kind := o.InvolvedObject.Kind
+	name := o.InvolvedObject.Name
+	namespace := o.InvolvedObject.Namespace
+
+	// Get token from cache.
+	token, _, err := o.Cache.GetOrSet(ctx, cacheKey, func(ctx context.Context) (cache.Token, error) {
+		return newToken()
+	}, cache.WithInvolvedObject(kind, name, namespace))
+	if err != nil {
+		return nil, err
+	}
+
+	return token, nil
+}
+
+func newServiceAccountToken(ctx context.Context, client client.Client,
+	serviceAccount corev1.ServiceAccount, providerAudience string) (string, error) {
+	tokenReq := &authnv1.TokenRequest{
+		Spec: authnv1.TokenRequestSpec{
+			Audiences: []string{providerAudience},
+		},
+	}
+	if err := client.SubResource("token").Create(ctx, &serviceAccount, tokenReq); err != nil {
+		return "", fmt.Errorf("failed to create kubernetes service account token: %w", err)
+	}
+	return tokenReq.Status.Token, nil
+}
+
+func buildCacheKey(provider Provider, providerIdentity string,
+	serviceAccount *corev1.ServiceAccount, opts ...Option) string {
+
+	var o Options
+	o.Apply(opts...)
+
+	var keyParts []string
+
+	keyParts = append(keyParts, fmt.Sprintf("provider=%s", provider.GetName()))
+
+	if serviceAccount != nil {
+		keyParts = append(keyParts, fmt.Sprintf("providerIdentity=%s", providerIdentity))
+		keyParts = append(keyParts, fmt.Sprintf("serviceAccountName=%s", serviceAccount.Name))
+		keyParts = append(keyParts, fmt.Sprintf("serviceAccountNamespace=%s", serviceAccount.Namespace))
+	}
+
+	if len(o.Scopes) > 0 {
+		keyParts = append(keyParts, fmt.Sprintf("scopes=%s", strings.Join(o.Scopes, ",")))
+	}
+
+	if o.ArtifactRepository != "" {
+		keyParts = append(keyParts, fmt.Sprintf("artifactRepositoryKey=%s", provider.GetArtifactCacheKey(o.ArtifactRepository)))
+	}
+
+	if o.STSEndpoint != "" {
+		keyParts = append(keyParts, fmt.Sprintf("stsEndpoint=%s", o.STSEndpoint))
+	}
+
+	if o.ProxyURL != nil {
+		keyParts = append(keyParts, fmt.Sprintf("proxyURL=%s", o.ProxyURL.String()))
+	}
+
+	s := strings.Join(keyParts, ",")
+	hash := sha256.Sum256([]byte(s))
+	return fmt.Sprintf("%x", hash)
+}