azureblob,azurefiles: add support for client assertion based authentication

backend/azureblob/azureblob.go

@@ -984,6 +984,38 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		if err != nil {
 			return nil, fmt.Errorf("failed to acquire MSI token: %w", err)
 		}
+	case opt.ClientID != "" && opt.Tenant != "" && opt.MSIClientID != "":
+		// Workload Identity based authentication
+		var options azidentity.ManagedIdentityCredentialOptions
+		options.ID = azidentity.ClientID(opt.MSIClientID)
+
+		msiCred, err := azidentity.NewManagedIdentityCredential(&options)
+		if err != nil {
+			return nil, fmt.Errorf("failed to acquire MSI token: %w", err)
+		}
+
+		getClientAssertions := func(context.Context) (string, error) {
+			token, err := msiCred.GetToken(context.Background(), policy.TokenRequestOptions{
+				Scopes: []string{"api://AzureADTokenExchange"},
+			})
+
+			if err != nil {
+				return "", fmt.Errorf("failed to acquire MSI token: %w", err)
+			}
+
+			return token.Token, nil
+		}
+
+		assertOpts := &azidentity.ClientAssertionCredentialOptions{}
+		f.cred, err = azidentity.NewClientAssertionCredential(
+			opt.Tenant,
+			opt.ClientID,
+			getClientAssertions,
+			assertOpts)
+
+		if err != nil {
+			return nil, fmt.Errorf("failed to acquire client assertion token: %w", err)
+		}
 	case opt.UseAZ:
 		var options = azidentity.AzureCLICredentialOptions{}
 		f.cred, err = azidentity.NewAzureCLICredential(&options)

backend/azurefiles/azurefiles.go

@@ -569,6 +569,38 @@ func newFsFromOptions(ctx context.Context, name, root string, opt *Options) (fs.
 		if err != nil {
 			return nil, fmt.Errorf("failed to acquire MSI token: %w", err)
 		}
+	case opt.ClientID != "" && opt.Tenant != "" && opt.MSIClientID != "":
+		// Workload Identity based authentication
+		var options azidentity.ManagedIdentityCredentialOptions
+		options.ID = azidentity.ClientID(opt.MSIClientID)
+
+		msiCred, err := azidentity.NewManagedIdentityCredential(&options)
+		if err != nil {
+			return nil, fmt.Errorf("failed to acquire MSI token: %w", err)
+		}
+
+		getClientAssertions := func(context.Context) (string, error) {
+			token, err := msiCred.GetToken(context.Background(), policy.TokenRequestOptions{
+				Scopes: []string{"api://AzureADTokenExchange"},
+			})
+
+			if err != nil {
+				return "", fmt.Errorf("failed to acquire MSI token: %w", err)
+			}
+
+			return token.Token, nil
+		}
+
+		assertOpts := &azidentity.ClientAssertionCredentialOptions{}
+		cred, err = azidentity.NewClientAssertionCredential(
+			opt.Tenant,
+			opt.ClientID,
+			getClientAssertions,
+			assertOpts)
+
+		if err != nil {
+			return nil, fmt.Errorf("failed to acquire client assertion token: %w", err)
+		}
 	default:
 		return nil, errors.New("no authentication method configured")
 	}

docs/content/azureblob.md

@@ -297,6 +297,16 @@ be explicitly specified using exactly one of the `msi_object_id`,
 If none of `msi_object_id`, `msi_client_id`, or `msi_mi_res_id` is
 set, this is is equivalent to using `env_auth`.
 
+#### Fedrated Identity Credentials 
+
+If these variables are set, rclone will authenticate with fedrated identity.
+
+- `tenant_id`: tenant_id to authenticate in storage
+- `client_id`: client ID of the application the user will authenticate to storage
+- `msi_client_id`: managed identity client ID of the application the user will authenticate to
+
+By default "api://AzureADTokenExchange" is used as scope for token retrieval over MSI. This token is then exchanged for actual storage token using 'tenant_id' and 'client_id'.
+
 #### Azure CLI tool `az` {#use_az}
 
 Set to use the [Azure CLI tool `az`](https://learn.microsoft.com/en-us/cli/azure/)

docs/content/azurefiles.md

@@ -295,6 +295,16 @@ be explicitly specified using exactly one of the `msi_object_id`,
 
 If none of `msi_object_id`, `msi_client_id`, or `msi_mi_res_id` is
 set, this is is equivalent to using `env_auth`.
+
+#### Fedrated Identity Credentials 
+
+If these variables are set, rclone will authenticate with fedrated identity.
+
+- `tenant_id`: tenant_id to authenticate in storage
+- `client_id`: client ID of the application the user will authenticate to storage
+- `msi_client_id`: managed identity client ID of the application the user will authenticate to
+
+By default "api://AzureADTokenExchange" is used as scope for token retrieval over MSI. This token is then exchanged for actual storage token using 'tenant_id' and 'client_id'.
 	
 #### Azure CLI tool `az` {#use_az}
 Set to use the [Azure CLI tool `az`](https://learn.microsoft.com/en-us/cli/azure/)