[RFC-0010] Add azure auth library

auth/aws/credentials_provider.go

@@ -38,8 +38,8 @@ func NewCredentialsProvider(ctx context.Context, opts ...auth.Option) aws.Creden
 // Retrieve implements aws.CredentialsProvider.
 // The context is ignored, use the constructor to set the context.
 // This is because some callers of the library pass context.Background()
-// when calling this method, so to ensure we have a real context we pass
-// it in the constructor.
+// when calling this method (e.g. SOPS), so to ensure we have a real
+// context we pass it in the constructor.
 func (c *credentialsProvider) Retrieve(context.Context) (aws.Credentials, error) {
 	token, err := auth.GetToken(c.ctx, Provider{}, c.opts...)
 	if err != nil {

auth/azure/new_default_azure_credential.go

@@ -0,0 +1,91 @@
+/*
+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 azure
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
+	"github.com/Azure/azure-sdk-for-go/sdk/azidentity"
+)
+
+// newDefaultAzureCredential is like azidentity.NewDefaultAzureCredential(),
+// but does not call the functions that shell out to Azure CLIs.
+func newDefaultAzureCredential(options azidentity.DefaultAzureCredentialOptions) (azcore.TokenCredential, error) {
+	const (
+		azureClientID           = "AZURE_CLIENT_ID"
+		azureFederatedTokenFile = "AZURE_FEDERATED_TOKEN_FILE"
+		azureAuthorityHost      = "AZURE_AUTHORITY_HOST"
+		azureTenantID           = "AZURE_TENANT_ID"
+	)
+
+	var errorMessages []string
+
+	envCred, err := azidentity.NewEnvironmentCredential(&azidentity.EnvironmentCredentialOptions{
+		ClientOptions: options.ClientOptions, DisableInstanceDiscovery: options.DisableInstanceDiscovery},
+	)
+	if err == nil {
+		return envCred, nil
+	} else {
+		errorMessages = append(errorMessages, "EnvironmentCredential: "+err.Error())
+	}
+
+	// workload identity requires values for AZURE_AUTHORITY_HOST, AZURE_CLIENT_ID, AZURE_FEDERATED_TOKEN_FILE, AZURE_TENANT_ID
+	haveWorkloadConfig := false
+	clientID, haveClientID := os.LookupEnv(azureClientID)
+	if haveClientID {
+		if file, ok := os.LookupEnv(azureFederatedTokenFile); ok {
+			if _, ok := os.LookupEnv(azureAuthorityHost); ok {
+				if tenantID, ok := os.LookupEnv(azureTenantID); ok {
+					haveWorkloadConfig = true
+					workloadCred, err := azidentity.NewWorkloadIdentityCredential(&azidentity.WorkloadIdentityCredentialOptions{
+						ClientID:                 clientID,
+						TenantID:                 tenantID,
+						TokenFilePath:            file,
+						ClientOptions:            options.ClientOptions,
+						DisableInstanceDiscovery: options.DisableInstanceDiscovery,
+					})
+					if err == nil {
+						return workloadCred, nil
+					} else {
+						errorMessages = append(errorMessages, "Workload Identity"+": "+err.Error())
+					}
+				}
+			}
+		}
+	}
+	if !haveWorkloadConfig {
+		err := errors.New("missing environment variables for workload identity. Check webhook and pod configuration")
+		errorMessages = append(errorMessages, fmt.Sprintf("Workload Identity: %s", err))
+	}
+
+	o := &azidentity.ManagedIdentityCredentialOptions{ClientOptions: options.ClientOptions}
+	if haveClientID {
+		o.ID = azidentity.ClientID(clientID)
+	}
+	miCred, err := azidentity.NewManagedIdentityCredential(o)
+	if err == nil {
+		return miCred, nil
+	} else {
+		errorMessages = append(errorMessages, "ManagedIdentity"+": "+err.Error())
+	}
+
+	return nil, errors.New(strings.Join(errorMessages, "\n"))
+}