feat(auth): add Workload Identity Federation (OIDC) support

AUTHENTICATION.md

@@ -106,3 +106,28 @@ Using this flow is less secure since the token is long-lived. You can provide th
 1. Providing the flag `--service-account-token`
 2. Setting the environment variable `STACKIT_SERVICE_ACCOUNT_TOKEN`
 3. Setting `STACKIT_SERVICE_ACCOUNT_TOKEN` in the credentials file (see above)
+
+### Workload Identity Federation (OIDC)
+
+1. Create a service account trusted relation in the STACKIT Portal:
+
+   - Navigate to `Service Accounts` → Select account → `Federated Identity Providers`
+   - [Configure a Federated Identity Provider](https://docs.stackit.cloud/platform/access-and-identity/service-accounts/how-tos/manage-service-account-federations/#create-a-federated-identity-provider) and the required assertions. For detailed assertion configuration per platform, see the [Terraform provider WIF guide](https://github.com/stackitcloud/terraform-provider-stackit/blob/main/docs/guides/workload_identity_federation.md).
+
+2. Configure authentication for `stackit auth activate-service-account` using one of the options below:
+
+   - Explicit flag: `--use-oidc` (takes precedence)
+   - Environment variable: `STACKIT_USE_OIDC=1`
+
+   If both are provided, the explicit flag value is used.
+
+   Example using environment variables:
+
+   ```bash
+   STACKIT_USE_OIDC=1
+   STACKIT_SERVICE_ACCOUNT_EMAIL=my-sa@sa.stackit.cloud
+   # Optional: provide the OIDC token directly instead of auto-detecting it from the CI environment
+   STACKIT_SERVICE_ACCOUNT_FEDERATED_TOKEN=<oidc-token>
+   # Optional: provide a file path containing the OIDC token
+   STACKIT_FEDERATED_TOKEN_FILE=/path/to/oidc-token.jwt
+   ```

docs/stackit_auth_activate-service-account.md

@@ -26,6 +26,9 @@ stackit auth activate-service-account [flags]
 
   Only print the corresponding access token by using the service account token. This access token can be stored as environment variable (STACKIT_ACCESS_TOKEN) in order to be used for all subsequent commands.
   $ stackit auth activate-service-account --service-account-token my-service-account-token --only-print-access-token
+
+  Authenticate via Workload Identity Federation (OIDC) and print the short-lived access token. Use --use-oidc to explicitly enable OIDC (takes precedence over STACKIT_USE_OIDC); no service account key file is required.
+  $ STACKIT_SERVICE_ACCOUNT_EMAIL=ci@sa.stackit.cloud stackit auth activate-service-account --use-oidc --only-print-access-token
 ```
 
 ### Options
@@ -36,6 +39,7 @@ stackit auth activate-service-account [flags]
       --private-key-path string           RSA private key path. It takes precedence over the private key included in the service account key, if present
       --service-account-key-path string   Service account key path
       --service-account-token string      Service account long-lived access token
+      --use-oidc                          Use Workload Identity Federation (OIDC). If set, this takes precedence over STACKIT_USE_OIDC
 ```
 
 ### Options inherited from parent commands

internal/cmd/auth/activate-service-account/activate_service_account.go

@@ -25,13 +25,15 @@ const (
 	serviceAccountTokenFlag   = "service-account-token"
 	serviceAccountKeyPathFlag = "service-account-key-path"
 	privateKeyPathFlag        = "private-key-path"
+	useOIDCFlag               = "use-oidc"
 	onlyPrintAccessTokenFlag  = "only-print-access-token" // #nosec G101
 )
 
 type inputModel struct {
 	ServiceAccountToken   string
 	ServiceAccountKeyPath string
 	PrivateKeyPath        string
+	UseOIDC               *bool
 	OnlyPrintAccessToken  bool
 }
 
@@ -59,13 +61,22 @@ func NewCmd(params *types.CmdParams) *cobra.Command {
 				`Only print the corresponding access token by using the service account token. This access token can be stored as environment variable (STACKIT_ACCESS_TOKEN) in order to be used for all subsequent commands.`,
 				"$ stackit auth activate-service-account --service-account-token my-service-account-token --only-print-access-token",
 			),
+			examples.NewExample(
+				`Authenticate via Workload Identity Federation (OIDC) and print the short-lived access token. Use --use-oidc to explicitly enable OIDC (takes precedence over STACKIT_USE_OIDC); no service account key file is required.`,
+				"$ STACKIT_SERVICE_ACCOUNT_EMAIL=ci@sa.stackit.cloud stackit auth activate-service-account --use-oidc --only-print-access-token",
+			),
 		),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			model, err := parseInput(params.Printer, cmd, args)
 			if err != nil {
 				return err
 			}
 
+			// use workload identity federation (OIDC) if enabled; no key file required
+			if auth.IsOIDCEnabledWithOverride(model.UseOIDC) {
+				return runOIDCMode(params, model)
+			}
+
 			tokenCustomEndpoint := viper.GetString(config.TokenCustomEndpointKey)
 			if !model.OnlyPrintAccessToken {
 				if err := storeCustomEndpoint(tokenCustomEndpoint); err != nil {
@@ -115,6 +126,7 @@ func configureFlags(cmd *cobra.Command) {
 	cmd.Flags().String(serviceAccountTokenFlag, "", "Service account long-lived access token")
 	cmd.Flags().String(serviceAccountKeyPathFlag, "", "Service account key path")
 	cmd.Flags().String(privateKeyPathFlag, "", "RSA private key path. It takes precedence over the private key included in the service account key, if present")
+	cmd.Flags().Bool(useOIDCFlag, false, "Use Workload Identity Federation (OIDC). If set, this takes precedence over STACKIT_USE_OIDC")
 	cmd.Flags().Bool(onlyPrintAccessTokenFlag, false, "If this is set to true the credentials are not stored in either the keyring or a file")
 }
 
@@ -125,6 +137,10 @@ func parseInput(p *print.Printer, cmd *cobra.Command, _ []string) (*inputModel,
 		PrivateKeyPath:        flags.FlagToStringValue(p, cmd, privateKeyPathFlag),
 		OnlyPrintAccessToken:  flags.FlagToBoolValue(p, cmd, onlyPrintAccessTokenFlag),
 	}
+	if cmd.Flags().Changed(useOIDCFlag) {
+		useOIDC := flags.FlagToBoolValue(p, cmd, useOIDCFlag)
+		model.UseOIDC = &useOIDC
+	}
 
 	p.DebugInputModel(model)
 	return &model, nil
@@ -133,3 +149,50 @@ func parseInput(p *print.Printer, cmd *cobra.Command, _ []string) (*inputModel,
 func storeCustomEndpoint(tokenCustomEndpoint string) error {
 	return auth.SetAuthField(auth.TOKEN_CUSTOM_ENDPOINT, tokenCustomEndpoint)
 }
+
+func runOIDCMode(params *types.CmdParams, model *inputModel) error {
+	email := auth.OIDCServiceAccountEmail()
+	if email == "" {
+		return fmt.Errorf(
+			"env var %s must be set when %s is enabled",
+			auth.EnvServiceAccountEmail, auth.EnvUseOIDC,
+		)
+	}
+
+	tokenFunc, err := auth.OIDCTokenFunc()
+	if err != nil {
+		return err
+	}
+
+	tokenCustomEndpoint := viper.GetString(config.TokenCustomEndpointKey)
+
+	wifCfg := &sdkConfig.Configuration{
+		WorkloadIdentityFederation:       true,
+		ServiceAccountEmail:              email,
+		ServiceAccountFederatedTokenFunc: tokenFunc,
+		TokenCustomUrl:                   tokenCustomEndpoint,
+	}
+
+	rt, err := sdkAuth.SetupAuth(wifCfg)
+	if err != nil {
+		params.Printer.Debug(print.ErrorLevel, "setup workload identity federation auth: %v", err)
+		return &cliErr.ActivateServiceAccountError{}
+	}
+
+	// credentials are never written to disk in OIDC mode
+	saEmail, accessToken, err := auth.AuthenticateServiceAccount(params.Printer, rt, true)
+	if err != nil {
+		var activateErr *cliErr.ActivateServiceAccountError
+		if !errors.As(err, &activateErr) {
+			return fmt.Errorf("authenticate service account via workload identity federation: %w", err)
+		}
+		return err
+	}
+
+	if model.OnlyPrintAccessToken {
+		params.Printer.Outputf("%s\n", accessToken)
+	} else {
+		params.Printer.Outputf("Authenticated via Workload Identity Federation.\nService account email: %s\n", saEmail)
+	}
+	return nil
+}

internal/cmd/auth/activate-service-account/activate_service_account_test.go

@@ -14,11 +14,16 @@ import (
 
 var testTokenCustomEndpoint = "token_url"
 
+func boolPtr(v bool) *bool {
+	return &v
+}
+
 func fixtureFlagValues(mods ...func(flagValues map[string]string)) map[string]string {
 	flagValues := map[string]string{
 		serviceAccountTokenFlag:   "token",
 		serviceAccountKeyPathFlag: "sa_key",
 		privateKeyPathFlag:        "private_key",
+		useOIDCFlag:               "true",
 		onlyPrintAccessTokenFlag:  "true",
 	}
 	for _, mod := range mods {
@@ -32,6 +37,7 @@ func fixtureInputModel(mods ...func(model *inputModel)) *inputModel {
 		ServiceAccountToken:   "token",
 		ServiceAccountKeyPath: "sa_key",
 		PrivateKeyPath:        "private_key",
+		UseOIDC:               boolPtr(true),
 		OnlyPrintAccessToken:  true,
 	}
 	for _, mod := range mods {
@@ -65,6 +71,7 @@ func TestParseInput(t *testing.T) {
 				ServiceAccountToken:   "",
 				ServiceAccountKeyPath: "",
 				PrivateKeyPath:        "",
+				UseOIDC:               nil,
 			},
 		},
 		{
@@ -80,8 +87,29 @@ func TestParseInput(t *testing.T) {
 				ServiceAccountToken:   "",
 				ServiceAccountKeyPath: "",
 				PrivateKeyPath:        "",
+				UseOIDC:               nil,
 			},
 		},
+		{
+			description: "use_oidc_true",
+			flagValues: fixtureFlagValues(func(flagValues map[string]string) {
+				flagValues[useOIDCFlag] = "true"
+			}),
+			isValid: true,
+			expectedModel: fixtureInputModel(func(model *inputModel) {
+				model.UseOIDC = boolPtr(true)
+			}),
+		},
+		{
+			description: "use_oidc_false",
+			flagValues: fixtureFlagValues(func(flagValues map[string]string) {
+				flagValues[useOIDCFlag] = "false"
+			}),
+			isValid: true,
+			expectedModel: fixtureInputModel(func(model *inputModel) {
+				model.UseOIDC = boolPtr(false)
+			}),
+		},
 		{
 			description: "invalid_flag",
 			flagValues: fixtureFlagValues(func(flagValues map[string]string) {
@@ -101,6 +129,18 @@ func TestParseInput(t *testing.T) {
 				model.OnlyPrintAccessToken = false
 			}),
 		},
+		{
+			description: "default value UseOIDC",
+			flagValues: fixtureFlagValues(
+				func(flagValues map[string]string) {
+					delete(flagValues, useOIDCFlag)
+				},
+			),
+			isValid: true,
+			expectedModel: fixtureInputModel(func(model *inputModel) {
+				model.UseOIDC = nil
+			}),
+		},
 	}
 
 	for _, tt := range tests {

internal/pkg/auth/auth.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/golang-jwt/jwt/v5"
 	"github.com/spf13/viper"
+	sdkAuth "github.com/stackitcloud/stackit-sdk-go/core/auth"
 	sdkConfig "github.com/stackitcloud/stackit-sdk-go/core/config"
 )
 
@@ -33,6 +34,38 @@ func AuthenticationConfig(p *print.Printer, reauthorizeUserRoutine func(p *print
 		return authCfgOption, nil
 	}
 
+	// use workload identity federation (OIDC) if enabled; takes priority over stored flows
+	if IsOIDCEnabled() {
+		p.Debug(print.DebugLevel, "authenticating using workload identity federation (OIDC)")
+
+		email := OIDCServiceAccountEmail()
+		if email == "" {
+			return nil, fmt.Errorf(
+				"env var %s must be set when %s is enabled",
+				EnvServiceAccountEmail, EnvUseOIDC,
+			)
+		}
+
+		tokenFunc, err := OIDCTokenFunc()
+		if err != nil {
+			return nil, err
+		}
+
+		wifCfg := &sdkConfig.Configuration{
+			WorkloadIdentityFederation:       true,
+			ServiceAccountEmail:              email,
+			ServiceAccountFederatedTokenFunc: tokenFunc,
+			TokenCustomUrl:                   viper.GetString(config.TokenCustomEndpointKey),
+		}
+
+		rt, err := sdkAuth.WorkloadIdentityFederationAuth(wifCfg)
+		if err != nil {
+			return nil, fmt.Errorf("initialize workload identity federation: %w", err)
+		}
+
+		return sdkConfig.WithCustomAuth(rt), nil
+	}
+
 	flow, err := GetAuthFlow()
 	if err != nil {
 		return nil, fmt.Errorf("get authentication flow: %w", err)

internal/pkg/auth/auth_test.go

@@ -155,6 +155,7 @@ func TestAuthenticationConfig(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.description, func(t *testing.T) {
+			t.Setenv(EnvUseOIDC, "") // ensure OIDC mode is off for these tests
 			keyring.MockInit()
 			timestamp := time.Now().Add(24 * time.Hour)
 			authFields := make(map[authFieldKey]string)

internal/pkg/auth/oidc.go

@@ -0,0 +1,80 @@
+package auth
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/stackitcloud/stackit-sdk-go/core/oidcadapters"
+)
+
+const (
+	EnvUseOIDC                      = "STACKIT_USE_OIDC"
+	EnvServiceAccountEmail          = "STACKIT_SERVICE_ACCOUNT_EMAIL"
+	EnvServiceAccountFederatedToken = "STACKIT_SERVICE_ACCOUNT_FEDERATED_TOKEN" //nolint:gosec // linter false positive
+	EnvFederatedTokenFile           = "STACKIT_FEDERATED_TOKEN_FILE"
+	EnvGitHubRequestURL             = "ACTIONS_ID_TOKEN_REQUEST_URL"
+	EnvGitHubRequestToken           = "ACTIONS_ID_TOKEN_REQUEST_TOKEN" //nolint:gosec // linter false positive
+	EnvAzureOIDCRequestURI          = "SYSTEM_OIDCREQUESTURI"
+	EnvAzureAccessToken             = "SYSTEM_ACCESSTOKEN" //nolint:gosec // linter false positive
+)
+
+func IsOIDCEnabled() bool {
+	return os.Getenv(EnvUseOIDC) == "1"
+}
+
+// IsOIDCEnabledWithOverride resolves OIDC mode using explicit input first and env fallback.
+// If useOIDC is not nil, its value is used directly; otherwise STACKIT_USE_OIDC is evaluated.
+func IsOIDCEnabledWithOverride(useOIDC *bool) bool {
+	if useOIDC != nil {
+		return *useOIDC
+	}
+
+	return IsOIDCEnabled()
+}
+
+func OIDCServiceAccountEmail() string {
+	return os.Getenv(EnvServiceAccountEmail)
+}
+
+// TokenFunc returns the OIDCTokenFunc to use for Workload Identity Federation.
+// It checks the following token sources in order: STACKIT_SERVICE_ACCOUNT_FEDERATED_TOKEN,
+// STACKIT_FEDERATED_TOKEN_FILE, GitHub Actions (ACTIONS_ID_TOKEN_REQUEST_URL +
+// ACTIONS_ID_TOKEN_REQUEST_TOKEN), and Azure DevOps (SYSTEM_OIDCREQUESTURI + SYSTEM_ACCESSTOKEN).
+// Returns an error if no source is detected.
+func OIDCTokenFunc() (oidcadapters.OIDCTokenFunc, error) {
+	// static token provided directly via env var
+	if token := os.Getenv(EnvServiceAccountFederatedToken); token != "" {
+		return func(_ context.Context) (string, error) {
+			return token, nil
+		}, nil
+	}
+
+	// token read from filesystem path via env var
+	if tokenFilePath := os.Getenv(EnvFederatedTokenFile); tokenFilePath != "" {
+		return oidcadapters.ReadJWTFromFileSystem(tokenFilePath), nil
+	}
+
+	// GitHub Actions
+	if ghURL := os.Getenv(EnvGitHubRequestURL); ghURL != "" {
+		if ghToken := os.Getenv(EnvGitHubRequestToken); ghToken != "" {
+			return oidcadapters.RequestGHOIDCToken(ghURL, ghToken), nil
+		}
+	}
+
+	// Azure DevOps
+	if adoURL := os.Getenv(EnvAzureOIDCRequestURI); adoURL != "" {
+		if adoToken := os.Getenv(EnvAzureAccessToken); adoToken != "" {
+			return oidcadapters.RequestAzureDevOpsOIDCToken(adoURL, adoToken, ""), nil
+		}
+	}
+
+	return nil, fmt.Errorf(
+		"%s is enabled but no OIDC token source was detected\n"+
+			"Provide the token via %s or %s, or run in a supported CI environment:\n"+
+			"  - GitHub Actions: grant 'id-token: write' permission; %s and %s are set automatically by the runner\n"+
+			"  - Azure DevOps:   pass 'SYSTEM_ACCESSTOKEN: $(System.AccessToken)' in your pipeline step",
+		EnvUseOIDC, EnvServiceAccountFederatedToken, EnvFederatedTokenFile,
+		EnvGitHubRequestURL, EnvGitHubRequestToken,
+	)
+}