Azure: add option to force use of CLI credential

changelog/unreleased/pull-4799

@@ -0,0 +1,5 @@
+Enhancement: Add option to force use of Azure CLI credential
+
+A new environment variable `AZURE_FORCE_CLI_CREDENTIAL=true` allows forcing the use of Azure CLI credential, ignoring other credentials like managed identity.
+
+https://github.com/restic/restic/pull/4799

doc/030_preparing_a_new_repo.rst

@@ -548,9 +548,23 @@ For authentication export one of the following variables:
     # For SAS
     $ export AZURE_ACCOUNT_SAS=<SAS_TOKEN>
 
-Alternatively, if run on Azure, restic will automatically uses service accounts configured
+For authentication using ``az login`` ensure the user has
+the minimum permissions of the role assignment ``Storage Blob Data Contributor`` on Azure RBAC
+for the storage account.
+
+.. code-block:: console
+
+    $ az login
+
+Alternatively, if run on Azure, restic will automatically use service accounts configured
 via the standard environment variables or Workload / Managed Identities.
 
+To enforce the use of the Azure CLI credential when other credentials are present, set the following environment variable:
+
+.. code-block:: console
+
+    $ export AZURE_FORCE_CLI_CREDENTIAL=true
+
 Restic will by default use Azure's global domain ``core.windows.net`` as endpoint suffix.
 You can specify other suffixes as follows:
 

doc/040_backup.rst

@@ -597,6 +597,7 @@ environment variables. The following lists these environment variables:
     AZURE_ACCOUNT_KEY                   Account key for Azure
     AZURE_ACCOUNT_SAS                   Shared access signatures (SAS) for Azure
     AZURE_ENDPOINT_SUFFIX               Endpoint suffix for Azure Storage (default: core.windows.net)
+    AZURE_FORCE_CLI_CREDENTIAL          Force the use of Azure CLI credentials for authentication
 
     B2_ACCOUNT_ID                       Account ID or applicationKeyId for Backblaze B2
     B2_ACCOUNT_KEY                      Account Key or applicationKey for Backblaze B2

internal/backend/azure/azure.go

@@ -101,6 +101,18 @@ func open(cfg Config, rt http.RoundTripper) (*Backend, error) {
 		if err != nil {
 			return nil, errors.Wrap(err, "NewAccountSASClientFromEndpointToken")
 		}
+	} else if cfg.ForceCliCredential {
+		debug.Log(" - using AzureCLICredential")
+
+		cred, err := azidentity.NewAzureCLICredential(nil)
+		if err != nil {
+			return nil, errors.Wrap(err, "NewAzureCLICredential")
+		}
+
+		client, err = azContainer.NewClient(url, cred, opts)
+		if err != nil {
+			return nil, errors.Wrap(err, "NewClient")
+		}
 	} else {
 		debug.Log(" - using DefaultAzureCredential")
 		cred, err := azidentity.NewDefaultAzureCredential(nil)

internal/backend/azure/config.go

@@ -3,6 +3,7 @@ package azure
 import (
 	"os"
 	"path"
+	"strconv"
 	"strings"
 
 	"github.com/restic/restic/internal/errors"
@@ -16,6 +17,7 @@ type Config struct {
 	AccountName        string
 	AccountSAS         options.SecretString
 	AccountKey         options.SecretString
+	ForceCliCredential bool
 	EndpointSuffix     string
 	Container          string
 	Prefix             string
@@ -73,6 +75,11 @@ func (cfg *Config) ApplyEnvironment(prefix string) {
 		cfg.AccountSAS = options.NewSecretString(os.Getenv(prefix + "AZURE_ACCOUNT_SAS"))
 	}
 
+	var forceCliCred, err = strconv.ParseBool(os.Getenv(prefix + "AZURE_FORCE_CLI_CREDENTIAL"))
+	if err == nil {
+		cfg.ForceCliCredential = forceCliCred
+	}
+
 	if cfg.EndpointSuffix == "" {
 		cfg.EndpointSuffix = os.Getenv(prefix + "AZURE_ENDPOINT_SUFFIX")
 	}