Add Workload Identity Federation (OIDC) authentication support (#1338)

* Add workload identity federation auth support

Adds anthropic_federation_rule_id, anthropic_organization_id,
anthropic_service_account_id, anthropic_workspace_id, and
anthropic_oidc_audience inputs. When the federation rule and organization
are set, the action fetches the workflow's GitHub Actions OIDC token,
writes it to a file in RUNNER_TEMP, keeps it refreshed during execution,
and points the Claude Code CLI at it via ANTHROPIC_IDENTITY_TOKEN_FILE so
the CLI can exchange it for a short-lived access token instead of using a
static API key.

* Add WIF example workflow and base-action federation docs

* Default workload identity OIDC audience to https://api.anthropic.com

base-action/README.md

@@ -91,6 +91,24 @@ Add the following to your workflow file:
     claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
 ```
 
+### Workload Identity Federation
+
+Instead of a static API key or OAuth token, you can authenticate via [Workload Identity Federation](https://platform.claude.com/docs/en/manage-claude/workload-identity-federation) by setting the federation environment variables on the step. Fetch an OIDC identity token from your provider, write it to a file, and point the action at it:
+
+```yaml
+- name: Run Claude Code with workload identity federation
+  uses: anthropics/claude-code-base-action@beta
+  with:
+    prompt: "Your prompt here"
+  env:
+    ANTHROPIC_FEDERATION_RULE_ID: fdrl_xxxxxxxxxxxx
+    ANTHROPIC_ORGANIZATION_ID: 00000000-0000-0000-0000-000000000000
+    ANTHROPIC_SERVICE_ACCOUNT_ID: svac_xxxxxxxxxxxx
+    ANTHROPIC_IDENTITY_TOKEN_FILE: /path/to/identity-token
+```
+
+Note: the base action does not fetch or refresh the identity token itself — you are responsible for providing a valid token file. [`anthropics/claude-code-action`](https://github.com/anthropics/claude-code-action) handles fetching and refreshing the GitHub Actions OIDC token automatically via its `anthropic_federation_rule_id` input.
+
 ## Inputs
 
 | Input                     | Description                                                                                                             | Required | Default                      |

base-action/src/validate-env.ts

@@ -8,6 +8,14 @@ export function validateEnvironmentVariables() {
   const useFoundry = process.env.CLAUDE_CODE_USE_FOUNDRY === "1";
   const anthropicApiKey = process.env.ANTHROPIC_API_KEY;
   const claudeCodeOAuthToken = process.env.CLAUDE_CODE_OAUTH_TOKEN;
+  const federationRuleId = process.env.ANTHROPIC_FEDERATION_RULE_ID;
+  const federationOrganizationId = process.env.ANTHROPIC_ORGANIZATION_ID;
+  const hasWorkloadIdentity = Boolean(
+    federationRuleId && federationOrganizationId,
+  );
+  const hasPartialWorkloadIdentity =
+    !hasWorkloadIdentity &&
+    Boolean(federationRuleId || federationOrganizationId);
 
   const errors: string[] = [];
 
@@ -20,10 +28,16 @@ export function validateEnvironmentVariables() {
   }
 
   if (!useBedrock && !useVertex && !useFoundry) {
-    if (!anthropicApiKey && !claudeCodeOAuthToken) {
-      errors.push(
-        "Either ANTHROPIC_API_KEY or CLAUDE_CODE_OAUTH_TOKEN is required when using direct Anthropic API.",
-      );
+    if (!anthropicApiKey && !claudeCodeOAuthToken && !hasWorkloadIdentity) {
+      if (hasPartialWorkloadIdentity) {
+        errors.push(
+          "Workload identity federation requires both ANTHROPIC_FEDERATION_RULE_ID and ANTHROPIC_ORGANIZATION_ID to be set.",
+        );
+      } else {
+        errors.push(
+          "Either ANTHROPIC_API_KEY, CLAUDE_CODE_OAUTH_TOKEN, or workload identity federation (ANTHROPIC_FEDERATION_RULE_ID and ANTHROPIC_ORGANIZATION_ID) is required when using direct Anthropic API.",
+        );
+      }
     }
   } else if (useBedrock) {
     const awsRegion = process.env.AWS_REGION;

base-action/test/validate-env.test.ts

@@ -11,6 +11,8 @@ describe("validateEnvironmentVariables", () => {
     originalEnv = { ...process.env };
     // Clear relevant environment variables
     delete process.env.ANTHROPIC_API_KEY;
+    delete process.env.ANTHROPIC_FEDERATION_RULE_ID;
+    delete process.env.ANTHROPIC_ORGANIZATION_ID;
     delete process.env.CLAUDE_CODE_USE_BEDROCK;
     delete process.env.CLAUDE_CODE_USE_VERTEX;
     delete process.env.CLAUDE_CODE_USE_FOUNDRY;
@@ -42,7 +44,32 @@ describe("validateEnvironmentVariables", () => {
 
     test("should fail when ANTHROPIC_API_KEY is missing", () => {
       expect(() => validateEnvironmentVariables()).toThrow(
-        "Either ANTHROPIC_API_KEY or CLAUDE_CODE_OAUTH_TOKEN is required when using direct Anthropic API.",
+        "Either ANTHROPIC_API_KEY, CLAUDE_CODE_OAUTH_TOKEN, or workload identity federation (ANTHROPIC_FEDERATION_RULE_ID and ANTHROPIC_ORGANIZATION_ID) is required when using direct Anthropic API.",
+      );
+    });
+
+    test("should pass when workload identity federation variables are provided", () => {
+      process.env.ANTHROPIC_FEDERATION_RULE_ID = "fdrl_test";
+      process.env.ANTHROPIC_ORGANIZATION_ID =
+        "00000000-0000-0000-0000-000000000000";
+
+      expect(() => validateEnvironmentVariables()).not.toThrow();
+    });
+
+    test("should fail when only ANTHROPIC_FEDERATION_RULE_ID is provided", () => {
+      process.env.ANTHROPIC_FEDERATION_RULE_ID = "fdrl_test";
+
+      expect(() => validateEnvironmentVariables()).toThrow(
+        "Workload identity federation requires both ANTHROPIC_FEDERATION_RULE_ID and ANTHROPIC_ORGANIZATION_ID to be set.",
+      );
+    });
+
+    test("should fail when only ANTHROPIC_ORGANIZATION_ID is provided", () => {
+      process.env.ANTHROPIC_ORGANIZATION_ID =
+        "00000000-0000-0000-0000-000000000000";
+
+      expect(() => validateEnvironmentVariables()).toThrow(
+        "Workload identity federation requires both ANTHROPIC_FEDERATION_RULE_ID and ANTHROPIC_ORGANIZATION_ID to be set.",
       );
     });
   });