feat: [CI-19349]: Added oidc support for ACR (#154)

* feat: [CI-18693]: Added oidc support for ACR

* feat: [CI-19349]: error handling

* feat: [CI-19349]: Refactored the code and added cli flags

* feat: [CI-19349]: Added test cases

* Update cmd/kaniko-acr/main.go

* Update cmd/kaniko-acr/main.go

* Update cmd/kaniko-acr/main.go

* feat: [CI-19349]: changed the variable names

* feat: [CI-18693]: Added error handling

* feat: [CI-19349]: removed redundant code

---------

Co-authored-by: OP (oppenheimer) <21008429+Ompragash@users.noreply.github.com>

README.md

@@ -53,6 +53,45 @@ docker build \
   --file docker/ecr/Dockerfile.linux.amd64 --tag plugins/kaniko-ecr .
 ```
 
+### Enhanced Build Arguments Support
+
+The drone-kaniko plugin now supports an improved build arguments system with the `CustomStringSliceFlag` implementation. This feature provides a more flexible way to pass multiple build arguments to your Docker builds.
+
+#### Multiple Build Arguments with Semicolon Delimiter
+
+A new custom CLI flag type that allows passing multiple build arguments using semicolon (`;`) as a delimiter. This flag is available across all registry implementations:
+
+- `kaniko-docker`
+- `kaniko-gcr` (Google Container Registry)
+- `kaniko-ecr` (Amazon Elastic Container Registry)
+- `kaniko-acr` (Azure Container Registry)
+- `kaniko-gar` (Google Artifact Registry)
+
+**Usage:**
+
+```console
+docker run --rm \
+    -e PLUGIN_BUILD_ARGS_NEW="ARG1=value1;ARG2=value2;ARG3=value3" \
+    -e PLUGIN_REPO=foo/bar \
+    -v $(pwd):/drone \
+    -w /drone \
+    plugins/kaniko:linux-amd64
+```
+
+#### For build args containing commas
+
+When your build arguments contain commas, enable the `PLUGIN_MULTIPLE_BUILD_ARGS` flag:
+
+```console
+docker run --rm \
+    -e PLUGIN_MULTIPLE_BUILD_ARGS=true \
+    -e PLUGIN_BUILD_ARGS_NEW="KEY1=value,with,comma;KEY2=another,value" \
+    -e PLUGIN_REPO=foo/bar \
+    -v $(pwd):/drone \
+    -w /drone \
+    plugins/kaniko:linux-amd64
+```
+
 ## Usage
 
 ### Operation Modes

cmd/kaniko-acr/main.go

@@ -20,8 +20,10 @@ import (
 	"github.com/urfave/cli"
 
 	kaniko "github.com/drone/drone-kaniko"
+	azureutil "github.com/drone/drone-kaniko/internal/azure"
 	"github.com/drone/drone-kaniko/pkg/artifact"
 	"github.com/drone/drone-kaniko/pkg/docker"
+	"github.com/drone/drone-kaniko/pkg/utils"
 )
 
 const (
@@ -98,6 +100,17 @@ func main() {
 			Usage:  "build args",
 			EnvVar: "PLUGIN_BUILD_ARGS",
 		},
+		cli.GenericFlag{
+			Name:   "args-new",
+			Usage:  "build args new",
+			EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+			Value:  new(utils.CustomStringSliceFlag),
+		},
+		cli.BoolFlag{
+			Name:   "plugin-multiple-build-agrs",
+			Usage:  "plugin multiple build agrs",
+			EnvVar: "PLUGIN_MULTIPLE_BUILD_ARGS",
+		},
 		cli.StringFlag{
 			Name:   "target",
 			Usage:  "build target",
@@ -156,7 +169,7 @@ func main() {
 		cli.StringFlag{
 			Name:   "tenant-id",
 			Usage:  "Azure Tenant Id",
-			EnvVar: "TENANT_ID",
+			EnvVar: "TENANT_ID,AZURE_TENANT_ID,PLUGIN_TENANT_ID",
 		},
 		cli.StringFlag{
 			Name:   "subscription-id",
@@ -165,8 +178,18 @@ func main() {
 		},
 		cli.StringFlag{
 			Name:   "client-id",
-			Usage:  "Azure Client Id",
-			EnvVar: "CLIENT_ID",
+			Usage:  "Azure Client ID (also called App ID)",
+			EnvVar: "CLIENT_ID,AZURE_CLIENT_ID,PLUGIN_CLIENT_ID,AZURE_APP_ID",
+		},
+		cli.StringFlag{
+			Name:   "oidc-token-id",
+			Usage:  "OIDC ID token to exchange for Azure AD access token (federated credentials)",
+			EnvVar: "PLUGIN_OIDC_TOKEN_ID",
+		},
+		cli.StringFlag{
+			Name:   "azure-authority-host",
+			Usage:  "Azure authority host base URL (e.g., https://login.microsoftonline.com, https://login.microsoftonline.us)",
+			EnvVar: "AZURE_AUTHORITY_HOST",
 		},
 		cli.StringFlag{
 			Name:   "snapshot-mode",
@@ -405,9 +428,17 @@ func run(c *cli.Context) error {
 	registry := c.String("registry")
 	noPush := c.Bool("no-push")
 
-	publicUrl, err := setupAuth(
-		c.String("tenant-id"),
-		c.String("client-id"),
+	clientID := c.String("client-id")
+	tenantID := c.String("tenant-id")
+	oidcIdToken := c.String("oidc-token-id")
+	authorityHost := c.String("azure-authority-host")
+
+	var publicUrl string
+	var err error
+	publicUrl, err = setupAuth(
+		tenantID,
+		clientID,
+		oidcIdToken,
 		c.String("client-cert"),
 		c.String("client-secret"),
 		c.String("subscription-id"),
@@ -415,6 +446,7 @@ func run(c *cli.Context) error {
 		c.String("base-image-username"),
 		c.String("base-image-password"),
 		c.String("base-image-registry"),
+		authorityHost,
 		noPush,
 	)
 	if err != nil {
@@ -432,6 +464,8 @@ func run(c *cli.Context) error {
 			AutoTagSuffix:               c.String("auto-tag-suffix"),
 			ExpandTag:                   c.Bool("expand-tag"),
 			Args:                        c.StringSlice("args"),
+			ArgsNew:                     c.Generic("args-new").(*utils.CustomStringSliceFlag).GetValue(),
+			IsMultipleBuildArgs:         c.Bool("plugin-multiple-build-agrs"),
 			Target:                      c.String("target"),
 			Repo:                        c.String("repo"),
 			Mirrors:                     c.StringSlice("registry-mirrors"),
@@ -502,40 +536,66 @@ func run(c *cli.Context) error {
 	return plugin.Exec()
 }
 
-func setupAuth(tenantId, clientId, cert,
-	clientSecret, subscriptionId, registry, dockerUsername, dockerPassword, dockerRegistry string, noPush bool) (string, error) {
+func setupAuth(tenantId, clientId, oidcIdToken, cert,
+	clientSecret, subscriptionId, registry, dockerUsername, dockerPassword, dockerRegistry, authorityHost string, noPush bool) (string, error) {
 	if registry == "" {
 		return "", fmt.Errorf("registry must be specified")
 	}
 
-	// case of client secret or cert based auth
-	if clientId != "" {
-		// only setup auth when pushing or credentials are defined
+	// Determine auth path: OIDC or Service Principal (secret/cert)
+	if tenantId == "" || clientId == "" {
+		if noPush {
+			logrus.Warnf("NO_PUSH mode: tenantId or clientId not provided")
+			return "", nil
+		}
+		return "", fmt.Errorf("tenantId and clientId must be provided")
+	}
 
-		token, publicUrl, err := getACRToken(subscriptionId, tenantId, clientId, clientSecret, cert, registry)
+	var aadAccessToken string
+	var acrToken string
+	var publicUrl string
+	var err error
+
+	if oidcIdToken != "" {
+		// Exchange OIDC ID token for AAD access token via client_assertion
+		aadAccessToken, err = azureutil.GetAADAccessTokenViaClientAssertion(context.Background(), tenantId, clientId, oidcIdToken, authorityHost)
 		if err != nil {
-			if noPush {
-				logrus.Warnf("NO_PUSH mode: failed to fetch ACR Token: %v", err)
-				return "", nil
-			}
-			return "", errors.Wrap(err, "failed to fetch ACR Token")
+			return handleError(noPush, err, "failed to get AAD token via OIDC")
 		}
-
-		// setup docker config for azure registry and base image docker registry
-		if err := setDockerAuth(username, token, registry, dockerUsername, dockerPassword, dockerRegistry); err != nil {
-			if noPush {
-				logrus.Warnf("NO_PUSH mode: failed to create docker config: %v", err)
-				return "", nil
-			}
-			return "", errors.Wrap(err, "failed to create docker config")
+		publicUrl, err = getPublicUrl(aadAccessToken, registry, subscriptionId)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "failed to get public url with error: %s\n", err)
+		}
+		// Exchange AAD access token to ACR refresh token
+		acrToken, err = fetchACRToken(tenantId, aadAccessToken, registry)
+		if err != nil {
+			return handleError(noPush, err, "failed to fetch ACR token")
+		}
+	} else if clientSecret != "" || cert != "" {
+		acrToken, publicUrl, err = getACRToken(subscriptionId, tenantId, clientId, clientSecret, cert, registry)
+		if err != nil {
+			return handleError(noPush, err, "failed to fetch ACR Token")
 		}
-		return publicUrl, nil
 	} else {
 		if noPush {
 			return "", nil
 		}
 		return "", fmt.Errorf("managed authentication is not supported")
 	}
+
+	if err := setDockerAuth(username, acrToken, registry, dockerUsername, dockerPassword, dockerRegistry); err != nil {
+		return handleError(noPush, err, "failed to create docker config")
+	}
+	return publicUrl, nil
+}
+
+// Error handling
+func handleError(noPush bool, err error, msg string) (string, error) {
+	if noPush {
+		logrus.Warnf("NO_PUSH mode: %s: %v", msg, err)
+		return "", nil
+	}
+	return "", errors.Wrap(err, msg)
 }
 
 func getACRToken(subscriptionId, tenantId, clientId, clientSecret, cert, registry string) (string, string, error) {
@@ -748,10 +808,18 @@ func handlePushOnly(c *cli.Context) error {
 		return fmt.Errorf("repository and registry must be specified for push-only operation")
 	}
 
-	// Setup ACR authentication
-	publicUrl, err := setupAuth(
-		c.String("tenant-id"),
-		c.String("client-id"),
+	// Resolve Azure client/tenant and OIDC via CLI flags
+	clientID := c.String("client-id")
+	tenantID := c.String("tenant-id")
+	oidcIdToken := c.String("oidc-token-id")
+	authorityHost := c.String("azure-authority-host")
+
+	var publicUrl string
+	var err error
+	publicUrl, err = setupAuth(
+		tenantID,
+		clientID,
+		oidcIdToken,
 		c.String("client-cert"),
 		c.String("client-secret"),
 		c.String("subscription-id"),
@@ -759,7 +827,8 @@ func handlePushOnly(c *cli.Context) error {
 		c.String("base-image-username"),
 		c.String("base-image-password"),
 		c.String("base-image-registry"),
-		false, // We want to push in push-only mode
+		authorityHost,
+		false,
 	)
 	if err != nil {
 		return err

cmd/kaniko-acr/main_test.go

@@ -9,7 +9,9 @@ import (
 	"testing"
 
 	"github.com/drone/drone-kaniko/pkg/docker"
+	"github.com/drone/drone-kaniko/pkg/utils"
 	"github.com/stretchr/testify/assert"
+	"github.com/urfave/cli"
 )
 
 const (
@@ -154,3 +156,234 @@ func TestCreateDockerConfigWithoutBaseRegistry(t *testing.T) {
 	_, exists := config.Auths[""]
 	assert.False(t, exists)
 }
+
+func TestCustomStringSliceFlagIntegration(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		{
+			name:     "single build arg",
+			input:    "ARG1=value1",
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "multiple build args with semicolon",
+			input:    "ARG1=value1;ARG2=value2;ARG3=value3",
+			expected: []string{"ARG1=value1", "ARG2=value2", "ARG3=value3"},
+		},
+		{
+			name:     "build args with spaces",
+			input:    "ARG1=value with spaces;ARG2=another value",
+			expected: []string{"ARG1=value with spaces", "ARG2=another value"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Test the CustomStringSliceFlag directly
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.input)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			result := flag.GetValue()
+			if len(result) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(result), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if result[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, result[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestCLIIntegrationWithCustomFlag(t *testing.T) {
+	// Test CLI integration with proper flag setup
+	tests := []struct {
+		name     string
+		args     []string
+		expected []string
+	}{
+		{
+			name:     "CLI with single arg",
+			args:     []string{"acr-test", "--args-new", "ARG1=value1"},
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "CLI with multiple args",
+			args:     []string{"acr-test", "--args-new", "ARG1=value1;ARG2=value2"},
+			expected: []string{"ARG1=value1", "ARG2=value2"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			app := cli.NewApp()
+			app.Name = "acr-test"
+
+			var capturedArgs []string
+
+			app.Flags = []cli.Flag{
+				cli.GenericFlag{
+					Name:   "args-new",
+					Usage:  "build args new",
+					EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+					Value:  new(utils.CustomStringSliceFlag),
+				},
+			}
+
+			app.Action = func(c *cli.Context) error {
+				if genericFlag := c.Generic("args-new"); genericFlag != nil {
+					if customFlag, ok := genericFlag.(*utils.CustomStringSliceFlag); ok {
+						capturedArgs = customFlag.GetValue()
+					}
+				}
+				return nil
+			}
+
+			err := app.Run(tt.args)
+			if err != nil {
+				t.Errorf("CLI run error = %v, want nil", err)
+				return
+			}
+
+			if len(capturedArgs) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(capturedArgs), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if capturedArgs[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, capturedArgs[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestACRBuildArgsProcessing(t *testing.T) {
+	// Test that build args are correctly processed in the context of ACR plugin
+	tests := []struct {
+		name          string
+		argsNew       string
+		expectedCount int
+		expectedFirst string
+	}{
+		{
+			name:          "docker build args format",
+			argsNew:       "GOOS=linux;GOARCH=amd64;CGO_ENABLED=0",
+			expectedCount: 3,
+			expectedFirst: "GOOS=linux",
+		},
+		{
+			name:          "azure specific args",
+			argsNew:       "AZURE_TENANT_ID=tenant123;AZURE_CLIENT_ID=client456",
+			expectedCount: 2,
+			expectedFirst: "AZURE_TENANT_ID=tenant123",
+		},
+		{
+			name:          "single complex arg with special characters",
+			argsNew:       "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+			expectedCount: 1,
+			expectedFirst: "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.argsNew)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			args := flag.GetValue()
+			if len(args) != tt.expectedCount {
+				t.Errorf("Got %d args, want %d", len(args), tt.expectedCount)
+				return
+			}
+
+			if len(args) > 0 && args[0] != tt.expectedFirst {
+				t.Errorf("Got first arg = %v, want %v", args[0], tt.expectedFirst)
+			}
+		})
+	}
+}
+
+func TestACRAuthenticationFlow(t *testing.T) {
+	// Test that ACR authentication works with build args
+	tests := []struct {
+		name         string
+		tenantId     string
+		clientId     string
+		clientSecret string
+		expectError  bool
+	}{
+		{
+			name:         "missing tenant id",
+			tenantId:     "",
+			clientId:     "client123",
+			clientSecret: "secret456",
+			expectError:  true,
+		},
+		{
+			name:         "missing client id",
+			tenantId:     "tenant123",
+			clientId:     "",
+			clientSecret: "secret456",
+			expectError:  true,
+		},
+		{
+			name:         "missing client secret",
+			tenantId:     "tenant123",
+			clientId:     "client456",
+			clientSecret: "",
+			expectError:  true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// This test validates the parameter validation logic
+			// without actually making network calls
+			if tt.tenantId == "" && !tt.expectError {
+				t.Error("Expected error for missing tenant ID")
+			}
+			if tt.clientId == "" && !tt.expectError {
+				t.Error("Expected error for missing client ID")
+			}
+			if tt.clientSecret == "" && !tt.expectError {
+				t.Error("Expected error for missing client secret")
+			}
+		})
+	}
+}
+
+func TestSetupAuth_RegistryMustBeSpecified(t *testing.T) {
+	pub, err := setupAuth("tenant", "client", "", "", "", "sub", "", "", "", "", "", false)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "registry must be specified")
+	assert.Equal(t, "", pub)
+}
+
+func TestSetupAuth_MissingTenantOrClient(t *testing.T) {
+	pub, err := setupAuth("tenant", "", "", "", "", "sub", "myregistry.azurecr.io", "", "", "", "", false)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "tenantId and clientId must be provided")
+	assert.Equal(t, "", pub)
+}
+
+func TestSetupAuth_NoCreds_NoPushTrue(t *testing.T) {
+	pub, err := setupAuth("tenant", "client", "", "", "", "sub", "myregistry.azurecr.io", "", "", "", "", true)
+	assert.NoError(t, err)
+	assert.Equal(t, "", pub)
+}

cmd/kaniko-docker/main.go

@@ -13,6 +13,7 @@ import (
 	kaniko "github.com/drone/drone-kaniko"
 	"github.com/drone/drone-kaniko/pkg/artifact"
 	"github.com/drone/drone-kaniko/pkg/docker"
+	"github.com/drone/drone-kaniko/pkg/utils"
 )
 
 const (
@@ -102,6 +103,17 @@ func main() {
 			Usage:  "build args",
 			EnvVar: "PLUGIN_BUILD_ARGS",
 		},
+		cli.GenericFlag{
+			Name:   "args-new",
+			Usage:  "build args new",
+			EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+			Value:  new(utils.CustomStringSliceFlag),
+		},
+		cli.BoolFlag{
+			Name:   "plugin-multiple-build-agrs",
+			Usage:  "plugin multiple build agrs",
+			EnvVar: "PLUGIN_MULTIPLE_BUILD_ARGS",
+		},
 		cli.StringFlag{
 			Name:   "target",
 			Usage:  "build target",
@@ -239,6 +251,7 @@ func main() {
 			Usage:  "Enable or disable compressed caching.",
 			EnvVar: "PLUGIN_COMPRESSED_CACHING",
 		},
+
 		cli.StringFlag{
 			Name:   "context-sub-path",
 			Usage:  "Sub-path within the context to build.",
@@ -421,6 +434,8 @@ func run(c *cli.Context) error {
 			AutoTagSuffix:               c.String("auto-tag-suffix"),
 			ExpandTag:                   c.Bool("expand-tag"),
 			Args:                        c.StringSlice("args"),
+			ArgsNew:                     c.Generic("args-new").(*utils.CustomStringSliceFlag).GetValue(),
+			IsMultipleBuildArgs:         c.Bool("plugin-multiple-build-agrs"),
 			Target:                      c.String("target"),
 			Repo:                        buildRepo(c.String("registry"), c.String("repo"), c.Bool("expand-repo")),
 			Mirrors:                     c.StringSlice("registry-mirrors"),

cmd/kaniko-docker/main_test.go

@@ -6,6 +6,8 @@ import (
 	"testing"
 
 	"github.com/drone/drone-kaniko/pkg/docker"
+	"github.com/drone/drone-kaniko/pkg/utils"
+	"github.com/urfave/cli"
 )
 
 func Test_buildRepo(t *testing.T) {
@@ -42,6 +44,168 @@ func Test_buildRepo(t *testing.T) {
 	}
 }
 
+func TestCustomStringSliceFlagIntegration(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		{
+			name:     "single build arg",
+			input:    "ARG1=value1",
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "multiple build args with semicolon",
+			input:    "ARG1=value1;ARG2=value2;ARG3=value3",
+			expected: []string{"ARG1=value1", "ARG2=value2", "ARG3=value3"},
+		},
+		{
+			name:     "build args with spaces",
+			input:    "ARG1=value with spaces;ARG2=another value",
+			expected: []string{"ARG1=value with spaces", "ARG2=another value"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Test the CustomStringSliceFlag directly
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.input)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			result := flag.GetValue()
+			if len(result) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(result), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if result[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, result[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestCLIIntegrationWithCustomFlag(t *testing.T) {
+	// Test CLI integration with proper flag setup
+	tests := []struct {
+		name     string
+		args     []string
+		expected []string
+	}{
+		{
+			name:     "CLI with single arg",
+			args:     []string{"docker-test", "--args-new", "ARG1=value1"},
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "CLI with multiple args",
+			args:     []string{"docker-test", "--args-new", "ARG1=value1;ARG2=value2"},
+			expected: []string{"ARG1=value1", "ARG2=value2"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			app := cli.NewApp()
+			app.Name = "docker-test"
+
+			var capturedArgs []string
+
+			app.Flags = []cli.Flag{
+				cli.GenericFlag{
+					Name:   "args-new",
+					Usage:  "build args new",
+					EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+					Value:  new(utils.CustomStringSliceFlag),
+				},
+			}
+
+			app.Action = func(c *cli.Context) error {
+				if genericFlag := c.Generic("args-new"); genericFlag != nil {
+					if customFlag, ok := genericFlag.(*utils.CustomStringSliceFlag); ok {
+						capturedArgs = customFlag.GetValue()
+					}
+				}
+				return nil
+			}
+
+			err := app.Run(tt.args)
+			if err != nil {
+				t.Errorf("CLI run error = %v, want nil", err)
+				return
+			}
+
+			if len(capturedArgs) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(capturedArgs), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if capturedArgs[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, capturedArgs[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestDockerBuildArgsProcessing(t *testing.T) {
+	// Test that build args are correctly processed in the context of Docker plugin
+	tests := []struct {
+		name          string
+		argsNew       string
+		expectedCount int
+		expectedFirst string
+	}{
+		{
+			name:          "docker build args format",
+			argsNew:       "GOOS=linux;GOARCH=amd64;CGO_ENABLED=0",
+			expectedCount: 3,
+			expectedFirst: "GOOS=linux",
+		},
+		{
+			name:          "single complex arg with special characters",
+			argsNew:       "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+			expectedCount: 1,
+			expectedFirst: "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+		},
+		{
+			name:          "args with equals and semicolons",
+			argsNew:       "API_URL=https://api.example.com;DEBUG=true;VERSION=1.0.0",
+			expectedCount: 3,
+			expectedFirst: "API_URL=https://api.example.com",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.argsNew)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			args := flag.GetValue()
+			if len(args) != tt.expectedCount {
+				t.Errorf("Got %d args, want %d", len(args), tt.expectedCount)
+				return
+			}
+
+			if len(args) > 0 && args[0] != tt.expectedFirst {
+				t.Errorf("Got first arg = %v, want %v", args[0], tt.expectedFirst)
+			}
+		})
+	}
+}
+
 func TestCreateDockerConfig(t *testing.T) {
 	config := docker.NewConfig()
 	tempDir, err := ioutil.TempDir("", "docker-config-test")

cmd/kaniko-ecr/main.go

@@ -30,6 +30,7 @@ import (
 	kaniko "github.com/drone/drone-kaniko"
 	"github.com/drone/drone-kaniko/pkg/artifact"
 	"github.com/drone/drone-kaniko/pkg/docker"
+	"github.com/drone/drone-kaniko/pkg/utils"
 	"github.com/google/go-containerregistry/pkg/authn"
 	"github.com/google/go-containerregistry/pkg/crane"
 )
@@ -132,7 +133,7 @@ func main() {
 			Name:   "args-new",
 			Usage:  "build args new",
 			EnvVar: "PLUGIN_BUILD_ARGS_NEW",
-			Value:  new(CustomStringSliceFlag),
+			Value:  new(utils.CustomStringSliceFlag),
 		},
 		cli.BoolFlag{
 			Name:   "plugin-multiple-build-agrs",
@@ -504,7 +505,7 @@ func run(c *cli.Context) error {
 			AutoTagSuffix:               c.String("auto-tag-suffix"),
 			ExpandTag:                   c.Bool("expand-tag"),
 			Args:                        c.StringSlice("args"),
-			ArgsNew:                     c.Generic("args-new").(*CustomStringSliceFlag).GetValue(),
+			ArgsNew:                     c.Generic("args-new").(*utils.CustomStringSliceFlag).GetValue(),
 			IsMultipleBuildArgs:         c.Bool("plugin-multiple-build-agrs"),
 			Target:                      c.String("target"),
 			Repo:                        fmt.Sprintf("%s/%s", c.String("registry"), c.String("repo")),

cmd/kaniko-ecr/main_test.go

@@ -7,7 +7,9 @@ import (
 	"testing"
 
 	"github.com/drone/drone-kaniko/pkg/docker"
+	"github.com/drone/drone-kaniko/pkg/utils"
 	"github.com/stretchr/testify/assert"
+	"github.com/urfave/cli"
 )
 
 func TestCreateDockerConfigForECRWithBaseRegistry(t *testing.T) {
@@ -43,3 +45,165 @@ func TestCreateDockerConfigForECRWithBaseRegistry(t *testing.T) {
 	expectedDockerAuth := docker.Auth{Auth: base64.StdEncoding.EncodeToString([]byte(dockerUsername + ":" + dockerPassword))}
 	assert.Equal(t, expectedDockerAuth, config.Auths[dockerRegistry])
 }
+
+func TestCustomStringSliceFlagIntegration(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		{
+			name:     "single build arg",
+			input:    "ARG1=value1",
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "multiple build args with semicolon",
+			input:    "ARG1=value1;ARG2=value2;ARG3=value3",
+			expected: []string{"ARG1=value1", "ARG2=value2", "ARG3=value3"},
+		},
+		{
+			name:     "build args with spaces",
+			input:    "ARG1=value with spaces;ARG2=another value",
+			expected: []string{"ARG1=value with spaces", "ARG2=another value"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Test the CustomStringSliceFlag directly
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.input)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			result := flag.GetValue()
+			if len(result) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(result), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if result[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, result[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestCLIIntegrationWithCustomFlag(t *testing.T) {
+	// Test CLI integration with proper flag setup
+	tests := []struct {
+		name     string
+		args     []string
+		expected []string
+	}{
+		{
+			name:     "CLI with single arg",
+			args:     []string{"ecr-test", "--args-new", "ARG1=value1"},
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "CLI with multiple args",
+			args:     []string{"ecr-test", "--args-new", "ARG1=value1;ARG2=value2"},
+			expected: []string{"ARG1=value1", "ARG2=value2"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			app := cli.NewApp()
+			app.Name = "ecr-test"
+
+			var capturedArgs []string
+
+			app.Flags = []cli.Flag{
+				cli.GenericFlag{
+					Name:   "args-new",
+					Usage:  "build args new",
+					EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+					Value:  new(utils.CustomStringSliceFlag),
+				},
+			}
+
+			app.Action = func(c *cli.Context) error {
+				if genericFlag := c.Generic("args-new"); genericFlag != nil {
+					if customFlag, ok := genericFlag.(*utils.CustomStringSliceFlag); ok {
+						capturedArgs = customFlag.GetValue()
+					}
+				}
+				return nil
+			}
+
+			err := app.Run(tt.args)
+			if err != nil {
+				t.Errorf("CLI run error = %v, want nil", err)
+				return
+			}
+
+			if len(capturedArgs) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(capturedArgs), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if capturedArgs[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, capturedArgs[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestECRBuildArgsProcessing(t *testing.T) {
+	// Test that build args are correctly processed in the context of ECR plugin
+	tests := []struct {
+		name          string
+		argsNew       string
+		expectedCount int
+		expectedFirst string
+	}{
+		{
+			name:          "docker build args format",
+			argsNew:       "GOOS=linux;GOARCH=amd64;CGO_ENABLED=0",
+			expectedCount: 3,
+			expectedFirst: "GOOS=linux",
+		},
+		{
+			name:          "aws specific args",
+			argsNew:       "AWS_REGION=us-west-2;AWS_ACCOUNT_ID=123456789012",
+			expectedCount: 2,
+			expectedFirst: "AWS_REGION=us-west-2",
+		},
+		{
+			name:          "single complex arg with special characters",
+			argsNew:       "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+			expectedCount: 1,
+			expectedFirst: "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.argsNew)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			args := flag.GetValue()
+			if len(args) != tt.expectedCount {
+				t.Errorf("Got %d args, want %d", len(args), tt.expectedCount)
+				return
+			}
+
+			if len(args) > 0 && args[0] != tt.expectedFirst {
+				t.Errorf("Got first arg = %v, want %v", args[0], tt.expectedFirst)
+			}
+		})
+	}
+}

cmd/kaniko-gar/main.go

@@ -18,6 +18,8 @@ import (
 	"github.com/drone/drone-kaniko/pkg/docker"
 	"github.com/google/go-containerregistry/pkg/authn"
 	"github.com/google/go-containerregistry/pkg/crane"
+	"github.com/drone/drone-kaniko/pkg/utils"
+
 )
 
 const (
@@ -96,6 +98,17 @@ func main() {
 			Usage:  "build args",
 			EnvVar: "PLUGIN_BUILD_ARGS",
 		},
+		cli.GenericFlag{
+			Name:   "args-new",
+			Usage:  "build args new",
+			EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+			Value:  new(utils.CustomStringSliceFlag),
+		},
+		cli.BoolFlag{
+			Name:   "plugin-multiple-build-agrs",
+			Usage:  "plugin multiple build agrs",
+			EnvVar: "PLUGIN_MULTIPLE_BUILD_ARGS",
+		},
 		cli.StringFlag{
 			Name:   "target",
 			Usage:  "build target",
@@ -401,6 +414,8 @@ func run(c *cli.Context) error {
 			AutoTagSuffix:               c.String("auto-tag-suffix"),
 			ExpandTag:                   c.Bool("expand-tag"),
 			Args:                        c.StringSlice("args"),
+			ArgsNew:                     c.Generic("args-new").(*utils.CustomStringSliceFlag).GetValue(),
+			IsMultipleBuildArgs:         c.Bool("plugin-multiple-build-agrs"),
 			Target:                      c.String("target"),
 			Repo:                        fmt.Sprintf("%s/%s", c.String("registry"), c.String("repo")),
 			Mirrors:                     c.StringSlice("registry-mirrors"),

cmd/kaniko-gar/main_test.go

@@ -0,0 +1,286 @@
+package main
+
+import (
+	"os"
+	"testing"
+
+	"github.com/drone/drone-kaniko/pkg/utils"
+	"github.com/urfave/cli"
+)
+
+func TestCustomStringSliceFlagIntegration(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		{
+			name:     "single build arg",
+			input:    "ARG1=value1",
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "multiple build args with semicolon",
+			input:    "ARG1=value1;ARG2=value2;ARG3=value3",
+			expected: []string{"ARG1=value1", "ARG2=value2", "ARG3=value3"},
+		},
+		{
+			name:     "build args with spaces",
+			input:    "ARG1=value with spaces;ARG2=another value",
+			expected: []string{"ARG1=value with spaces", "ARG2=another value"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Test the CustomStringSliceFlag directly
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.input)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			result := flag.GetValue()
+			if len(result) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(result), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if result[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, result[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestCLIIntegrationWithCustomFlag(t *testing.T) {
+	// Test CLI integration with proper flag setup
+	tests := []struct {
+		name     string
+		args     []string
+		expected []string
+	}{
+		{
+			name:     "CLI with single arg",
+			args:     []string{"gar-test", "--args-new", "ARG1=value1"},
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "CLI with multiple args",
+			args:     []string{"gar-test", "--args-new", "ARG1=value1;ARG2=value2"},
+			expected: []string{"ARG1=value1", "ARG2=value2"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			app := cli.NewApp()
+			app.Name = "gar-test"
+
+			var capturedArgs []string
+
+			app.Flags = []cli.Flag{
+				cli.GenericFlag{
+					Name:   "args-new",
+					Usage:  "build args new",
+					EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+					Value:  new(utils.CustomStringSliceFlag),
+				},
+			}
+
+			app.Action = func(c *cli.Context) error {
+				if genericFlag := c.Generic("args-new"); genericFlag != nil {
+					if customFlag, ok := genericFlag.(*utils.CustomStringSliceFlag); ok {
+						capturedArgs = customFlag.GetValue()
+					}
+				}
+				return nil
+			}
+
+			err := app.Run(tt.args)
+			if err != nil {
+				t.Errorf("CLI run error = %v, want nil", err)
+				return
+			}
+
+			if len(capturedArgs) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(capturedArgs), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if capturedArgs[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, capturedArgs[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestEnvironmentVariableIntegration(t *testing.T) {
+	// Test that environment variables work with CustomStringSliceFlag
+	originalEnv := os.Getenv("PLUGIN_BUILD_ARGS_NEW")
+	defer func() {
+		if originalEnv != "" {
+			os.Setenv("PLUGIN_BUILD_ARGS_NEW", originalEnv)
+		} else {
+			os.Unsetenv("PLUGIN_BUILD_ARGS_NEW")
+		}
+	}()
+
+	os.Setenv("PLUGIN_BUILD_ARGS_NEW", "ENV_ARG1=env_value1;ENV_ARG2=env_value2")
+
+	app := cli.NewApp()
+	app.Flags = []cli.Flag{
+		cli.GenericFlag{
+			Name:   "args-new",
+			Usage:  "build args new",
+			EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+			Value:  new(utils.CustomStringSliceFlag),
+		},
+	}
+
+	var capturedArgs []string
+	app.Action = func(c *cli.Context) error {
+		if flag := c.Generic("args-new"); flag != nil {
+			if customFlag, ok := flag.(*utils.CustomStringSliceFlag); ok {
+				capturedArgs = customFlag.GetValue()
+			}
+		}
+		return nil
+	}
+
+	err := app.Run([]string{"test"})
+	if err != nil {
+		t.Errorf("App.Run() error = %v, want nil", err)
+		return
+	}
+
+	expected := []string{"ENV_ARG1=env_value1", "ENV_ARG2=env_value2"}
+	if len(capturedArgs) != len(expected) {
+		t.Errorf("Environment variable test: got %d args, want %d", len(capturedArgs), len(expected))
+		return
+	}
+
+	for i, exp := range expected {
+		if capturedArgs[i] != exp {
+			t.Errorf("Environment variable test: got arg[%d] = %v, want %v", i, capturedArgs[i], exp)
+		}
+	}
+}
+
+func TestGARBuildArgsProcessing(t *testing.T) {
+	// Test that build args are correctly processed in the context of GAR plugin
+	tests := []struct {
+		name          string
+		argsNew       string
+		expectedCount int
+		expectedFirst string
+	}{
+		{
+			name:          "docker build args format",
+			argsNew:       "GOOS=linux;GOARCH=amd64;CGO_ENABLED=0",
+			expectedCount: 3,
+			expectedFirst: "GOOS=linux",
+		},
+		{
+			name:          "google cloud specific args",
+			argsNew:       "GOOGLE_APPLICATION_CREDENTIALS=/path/to/creds.json;PROJECT_ID=my-project",
+			expectedCount: 2,
+			expectedFirst: "GOOGLE_APPLICATION_CREDENTIALS=/path/to/creds.json",
+		},
+		{
+			name:          "single complex arg with special characters",
+			argsNew:       "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+			expectedCount: 1,
+			expectedFirst: "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.argsNew)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			args := flag.GetValue()
+			if len(args) != tt.expectedCount {
+				t.Errorf("Got %d args, want %d", len(args), tt.expectedCount)
+				return
+			}
+
+			if len(args) > 0 && args[0] != tt.expectedFirst {
+				t.Errorf("Got first arg = %v, want %v", args[0], tt.expectedFirst)
+			}
+		})
+	}
+}
+
+func TestGARRegistryFormatting(t *testing.T) {
+	// Test GAR-specific registry formatting
+	tests := []struct {
+		name     string
+		registry string
+		repo     string
+		expected string
+	}{
+		{
+			name:     "standard GAR format",
+			registry: "us-central1-docker.pkg.dev",
+			repo:     "my-project/my-repo/my-image",
+			expected: "us-central1-docker.pkg.dev/my-project/my-repo/my-image",
+		},
+		{
+			name:     "different region",
+			registry: "europe-west1-docker.pkg.dev",
+			repo:     "project123/repo456/image789",
+			expected: "europe-west1-docker.pkg.dev/project123/repo456/image789",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// This would be the format used in the GAR plugin
+			result := tt.registry + "/" + tt.repo
+			if result != tt.expected {
+				t.Errorf("GAR formatting: got %v, want %v", result, tt.expected)
+			}
+		})
+	}
+}
+
+func TestGARAuthSetup(t *testing.T) {
+	// Test GAR authentication setup
+	tests := []struct {
+		name           string
+		jsonKey        string
+		expectAuthFile bool
+	}{
+		{
+			name:           "with json key",
+			jsonKey:        `{"type":"service_account","project_id":"test"}`,
+			expectAuthFile: true,
+		},
+		{
+			name:           "without json key (workload identity)",
+			jsonKey:        "",
+			expectAuthFile: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// This simulates the auth setup logic
+			hasAuthFile := tt.jsonKey != ""
+			if hasAuthFile != tt.expectAuthFile {
+				t.Errorf("Auth file expectation: got %v, want %v", hasAuthFile, tt.expectAuthFile)
+			}
+		})
+	}
+}

cmd/kaniko-gcr/main.go

@@ -13,6 +13,7 @@ import (
 	kaniko "github.com/drone/drone-kaniko"
 	"github.com/drone/drone-kaniko/pkg/artifact"
 	"github.com/drone/drone-kaniko/pkg/docker"
+	"github.com/drone/drone-kaniko/pkg/utils"
 )
 
 const (
@@ -333,6 +334,18 @@ func main() {
 			Usage:  "Number of retries for downloading base images.",
 			EnvVar: "PLUGIN_IMAGE_DOWNLOAD_RETRY",
 		},
+		cli.GenericFlag{
+			Name:   "args-new",
+			Usage:  "build args new",
+			EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+			Value:  new(utils.CustomStringSliceFlag),
+		},
+		cli.BoolFlag{
+			Name:   "plugin-multiple-build-agrs",
+			Usage:  "plugin multiple build agrs",
+			EnvVar: "PLUGIN_MULTIPLE_BUILD_ARGS",
+		},
+		
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -378,6 +391,8 @@ func run(c *cli.Context) error {
 			AutoTagSuffix:               c.String("auto-tag-suffix"),
 			ExpandTag:                   c.Bool("expand-tag"),
 			Args:                        c.StringSlice("args"),
+			ArgsNew:                     c.Generic("args-new").(*utils.CustomStringSliceFlag).GetValue(),
+			IsMultipleBuildArgs:         c.Bool("plugin-multiple-build-agrs"),
 			Target:                      c.String("target"),
 			Repo:                        fmt.Sprintf("%s/%s", c.String("registry"), c.String("repo")),
 			Mirrors:                     c.StringSlice("registry-mirrors"),

cmd/kaniko-gcr/main_test.go

@@ -0,0 +1,270 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"testing"
+
+	"github.com/drone/drone-kaniko/pkg/utils"
+	"github.com/urfave/cli"
+)
+
+func TestCustomStringSliceFlagIntegration(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		{
+			name:     "single build arg",
+			input:    "ARG1=value1",
+			expected: []string{"ARG1=value1"},
+		},
+		{
+			name:     "multiple build args with semicolon",
+			input:    "ARG1=value1;ARG2=value2;ARG3=value3",
+			expected: []string{"ARG1=value1", "ARG2=value2", "ARG3=value3"},
+		},
+		{
+			name:     "build args with spaces",
+			input:    "ARG1=value with spaces;ARG2=another value",
+			expected: []string{"ARG1=value with spaces", "ARG2=another value"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Test the CustomStringSliceFlag directly
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.input)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			result := flag.GetValue()
+			if len(result) != len(tt.expected) {
+				t.Errorf("Got %d args, want %d", len(result), len(tt.expected))
+				return
+			}
+
+			for i, expected := range tt.expected {
+				if result[i] != expected {
+					t.Errorf("Got arg[%d] = %v, want %v", i, result[i], expected)
+				}
+			}
+		})
+	}
+}
+
+func TestEnvironmentVariableIntegration(t *testing.T) {
+	// Test that environment variables work with CustomStringSliceFlag
+	originalEnv := os.Getenv("PLUGIN_BUILD_ARGS_NEW")
+	defer func() {
+		if originalEnv != "" {
+			os.Setenv("PLUGIN_BUILD_ARGS_NEW", originalEnv)
+		} else {
+			os.Unsetenv("PLUGIN_BUILD_ARGS_NEW")
+		}
+	}()
+
+	os.Setenv("PLUGIN_BUILD_ARGS_NEW", "ENV_ARG1=env_value1;ENV_ARG2=env_value2")
+
+	app := cli.NewApp()
+	app.Flags = []cli.Flag{
+		cli.GenericFlag{
+			Name:   "args-new",
+			Usage:  "build args new",
+			EnvVar: "PLUGIN_BUILD_ARGS_NEW",
+			Value:  new(utils.CustomStringSliceFlag),
+		},
+	}
+
+	var capturedArgs []string
+	app.Action = func(c *cli.Context) error {
+		if flag := c.Generic("args-new"); flag != nil {
+			if customFlag, ok := flag.(*utils.CustomStringSliceFlag); ok {
+				capturedArgs = customFlag.GetValue()
+			}
+		}
+		return nil
+	}
+
+	err := app.Run([]string{"test"})
+	if err != nil {
+		t.Errorf("App.Run() error = %v, want nil", err)
+		return
+	}
+
+	expected := []string{"ENV_ARG1=env_value1", "ENV_ARG2=env_value2"}
+	if len(capturedArgs) != len(expected) {
+		t.Errorf("Environment variable test: got %d args, want %d", len(capturedArgs), len(expected))
+		return
+	}
+
+	for i, exp := range expected {
+		if capturedArgs[i] != exp {
+			t.Errorf("Environment variable test: got arg[%d] = %v, want %v", i, capturedArgs[i], exp)
+		}
+	}
+}
+
+func TestGCRBuildArgsProcessing(t *testing.T) {
+	// Test that build args are correctly processed in the context of GCR plugin
+	tests := []struct {
+		name          string
+		argsNew       string
+		expectedCount int
+		expectedFirst string
+	}{
+		{
+			name:          "docker build args format",
+			argsNew:       "GOOS=linux;GOARCH=amd64;CGO_ENABLED=0",
+			expectedCount: 3,
+			expectedFirst: "GOOS=linux",
+		},
+		{
+			name:          "google cloud specific args",
+			argsNew:       "GOOGLE_APPLICATION_CREDENTIALS=/path/to/creds.json;PROJECT_ID=my-project",
+			expectedCount: 2,
+			expectedFirst: "GOOGLE_APPLICATION_CREDENTIALS=/path/to/creds.json",
+		},
+		{
+			name:          "single complex arg with special characters",
+			argsNew:       "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+			expectedCount: 1,
+			expectedFirst: "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			flag := &utils.CustomStringSliceFlag{}
+			err := flag.Set(tt.argsNew)
+			if err != nil {
+				t.Errorf("Set() error = %v, want nil", err)
+				return
+			}
+
+			args := flag.GetValue()
+			if len(args) != tt.expectedCount {
+				t.Errorf("Got %d args, want %d", len(args), tt.expectedCount)
+				return
+			}
+
+			if len(args) > 0 && args[0] != tt.expectedFirst {
+				t.Errorf("Got first arg = %v, want %v", args[0], tt.expectedFirst)
+			}
+		})
+	}
+}
+
+func TestGCRRegistryFormatting(t *testing.T) {
+	// Test GCR-specific registry formatting
+	tests := []struct {
+		name     string
+		registry string
+		repo     string
+		expected string
+	}{
+		{
+			name:     "standard GCR format",
+			registry: "gcr.io",
+			repo:     "my-project/my-image",
+			expected: "gcr.io/my-project/my-image",
+		},
+		{
+			name:     "regional GCR",
+			registry: "us.gcr.io",
+			repo:     "project123/image456",
+			expected: "us.gcr.io/project123/image456",
+		},
+		{
+			name:     "european GCR",
+			registry: "eu.gcr.io",
+			repo:     "my-eu-project/my-app",
+			expected: "eu.gcr.io/my-eu-project/my-app",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// This would be the format used in the GCR plugin
+			result := tt.registry + "/" + tt.repo
+			if result != tt.expected {
+				t.Errorf("GCR formatting: got %v, want %v", result, tt.expected)
+			}
+		})
+	}
+}
+
+func TestGCRJSONKeyValidation(t *testing.T) {
+	// Test JSON key validation for GCR authentication
+	tests := []struct {
+		name      string
+		jsonKey   string
+		expectErr bool
+	}{
+		{
+			name:      "empty json key",
+			jsonKey:   "",
+			expectErr: false, // Empty is allowed (workload identity)
+		},
+		{
+			name:      "valid json structure",
+			jsonKey:   `{"type":"service_account","project_id":"test","private_key_id":"123"}`,
+			expectErr: false,
+		},
+		{
+			name:      "invalid json",
+			jsonKey:   `{invalid json}`,
+			expectErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// This simulates the JSON key validation that would happen in GCR
+			if tt.jsonKey != "" {
+				var data map[string]interface{}
+				err := json.Unmarshal([]byte(tt.jsonKey), &data)
+				if err != nil && !tt.expectErr {
+					t.Errorf("Expected no error for JSON key, got %v", err)
+				}
+				if err == nil && tt.expectErr {
+					t.Errorf("Expected error for JSON key, got nil")
+				}
+			}
+		})
+	}
+}
+
+func TestGCRAuthSetup(t *testing.T) {
+	// Test GCR authentication setup
+	tests := []struct {
+		name           string
+		jsonKey        string
+		expectAuthFile bool
+	}{
+		{
+			name:           "with json key",
+			jsonKey:        `{"type":"service_account","project_id":"test"}`,
+			expectAuthFile: true,
+		},
+		{
+			name:           "without json key (workload identity)",
+			jsonKey:        "",
+			expectAuthFile: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// This simulates the auth setup logic
+			hasAuthFile := tt.jsonKey != ""
+			if hasAuthFile != tt.expectAuthFile {
+				t.Errorf("Auth file expectation: got %v, want %v", hasAuthFile, tt.expectAuthFile)
+			}
+		})
+	}
+}

internal/azure/tokenutil.go

@@ -0,0 +1,72 @@
+package azure
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+const DefaultResource = "https://management.azure.com/"
+const defaultAuthorityHost = "https://login.microsoftonline.com"
+const defaultHTTPTimeout = 30 * time.Second
+
+// GetAADAccessTokenViaClientAssertion exchanges an external OIDC ID token for an Azure AD access token
+
+func GetAADAccessTokenViaClientAssertion(ctx context.Context, tenantID, clientID, oidcToken, authorityHost string) (string, error) {
+	resource := DefaultResource
+
+	form := url.Values{
+		"client_id":             {clientID},
+		"scope":                 {resource + ".default"},
+		"grant_type":            {"client_credentials"},
+		"client_assertion_type": {"urn:ietf:params:oauth:client-assertion-type:jwt-bearer"},
+		"client_assertion":      {oidcToken},
+	}
+	base := authorityHost
+	if strings.TrimSpace(base) == "" {
+		base = defaultAuthorityHost
+	}
+	base = strings.TrimRight(base, "/")
+	endpoint := fmt.Sprintf("%s/%s/oauth2/v2.0/token", base, tenantID)
+	client := &http.Client{Timeout: defaultHTTPTimeout}
+	req, err := http.NewRequestWithContext(ctx, "POST", endpoint, strings.NewReader(form.Encode()))
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set("Accept", "application/json")
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		var aadErr struct {
+			Error            string `json:"error"`
+			ErrorDescription string `json:"error_description"`
+		}
+		limited := io.LimitedReader{R: resp.Body, N: 4096}
+		_ = json.NewDecoder(&limited).Decode(&aadErr)
+		if aadErr.Error != "" {
+			return "", fmt.Errorf("AAD token request failed: status=%d, error=%s", resp.StatusCode, aadErr.Error)
+		}
+		return "", fmt.Errorf("AAD token request failed: status=%d", resp.StatusCode)
+	}
+	var payload struct {
+		AccessToken string `json:"access_token"`
+		TokenType   string `json:"token_type"`
+		ExpiresIn   int    `json:"expires_in"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
+		return "", err
+	}
+	if payload.AccessToken == "" {
+		return "", fmt.Errorf("AAD token response missing access_token")
+	}
+	return payload.AccessToken, nil
+}

internal/azure/tokenutil_test.go

@@ -0,0 +1,103 @@
+package azure
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestGetAADAccessTokenViaClientAssertion_Success(t *testing.T) {
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Fatalf("expected POST, got %s", r.Method)
+		}
+		if ct := r.Header.Get("Content-Type"); !strings.Contains(ct, "application/x-www-form-urlencoded") {
+			t.Fatalf("expected form content-type, got %s", ct)
+		}
+		if err := r.ParseForm(); err != nil {
+			t.Fatalf("failed parsing form: %v", err)
+		}
+		assertEq(t, r.Form.Get("client_id"), "client")
+		assertEq(t, r.Form.Get("grant_type"), "client_credentials")
+		assertEq(t, r.Form.Get("client_assertion_type"), "urn:ietf:params:oauth:client-assertion-type:jwt-bearer")
+		assertEq(t, r.Form.Get("client_assertion"), "idtoken")
+		assertEq(t, r.Form.Get("scope"), DefaultResource+".default")
+
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte(`{"access_token":"AT","token_type":"Bearer","expires_in":3600}`))
+	}))
+	defer ts.Close()
+
+	tok, err := GetAADAccessTokenViaClientAssertion(context.Background(), "tenant", "client", "idtoken", ts.URL)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if tok != "AT" {
+		t.Fatalf("expected access token AT, got %q", tok)
+	}
+}
+
+func TestGetAADAccessTokenViaClientAssertion_400WithErrorField(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		_, _ = w.Write([]byte(`{"error":"invalid_client","error_description":"bad"}`))
+	}))
+	defer ts.Close()
+
+	_, err := GetAADAccessTokenViaClientAssertion(context.Background(), "tenant", "client", "idtoken", ts.URL)
+	if err == nil || !strings.Contains(err.Error(), "status=400") || !strings.Contains(err.Error(), "invalid_client") {
+		t.Fatalf("expected 400 with invalid_client error, got %v", err)
+	}
+}
+
+func TestGetAADAccessTokenViaClientAssertion_400WithoutErrorField(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+		_, _ = w.Write([]byte("{}"))
+	}))
+	defer ts.Close()
+
+	_, err := GetAADAccessTokenViaClientAssertion(context.Background(), "tenant", "client", "idtoken", ts.URL)
+	if err == nil || !strings.Contains(err.Error(), "status=400") {
+		t.Fatalf("expected 400 error, got %v", err)
+	}
+}
+
+func TestGetAADAccessTokenViaClientAssertion_MalformedJSON(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte("not-json"))
+	}))
+	defer ts.Close()
+
+	_, err := GetAADAccessTokenViaClientAssertion(context.Background(), "tenant", "client", "idtoken", ts.URL)
+	if err == nil {
+		t.Fatalf("expected JSON decode error, got nil")
+	}
+}
+
+func TestGetAADAccessTokenViaClientAssertion_MissingAccessToken(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte(`{"token_type":"Bearer","expires_in":3600}`))
+	}))
+	defer ts.Close()
+
+	_, err := GetAADAccessTokenViaClientAssertion(context.Background(), "tenant", "client", "idtoken", ts.URL)
+	if err == nil || !strings.Contains(err.Error(), "missing access_token") {
+		t.Fatalf("expected missing access_token error, got %v", err)
+	}
+}
+
+func assertEq(t *testing.T, got, want string) {
+	t.Helper()
+	if got != want {
+		t.Fatalf("mismatch: got=%q want=%q", got, want)
+	}
+}

pkg/utils/custom_string_slice.go

@@ -1,4 +1,4 @@
-package main
+package utils
 
 import (
 	"strings"
@@ -10,6 +10,7 @@ type CustomStringSliceFlag struct {
 	Value []string
 }
 
+// GetValue returns the slice of strings stored in the flag
 func (f *CustomStringSliceFlag) GetValue() []string {
 	if f.Value == nil {
 		return make([]string, 0)
@@ -17,6 +18,7 @@ func (f *CustomStringSliceFlag) GetValue() []string {
 	return f.Value
 }
 
+// String returns a string representation of the flag
 func (f *CustomStringSliceFlag) String() string {
 	if f.Value == nil {
 		return ""
@@ -24,6 +26,7 @@ func (f *CustomStringSliceFlag) String() string {
 	return strings.Join(f.Value, ";")
 }
 
+// Set sets the value of the flag from a string
 func (f *CustomStringSliceFlag) Set(v string) error {
 	for _, s := range strings.Split(v, ";") {
 		s = strings.TrimSpace(s)