fix: enforce allowed-account-ids on the use-existing-credentials path

The early return for valid pre-existing credentials skipped the
allowed-account-ids check, now included.

src/helpers.ts

@@ -5,7 +5,6 @@ import type { Credentials, STSClient } from '@aws-sdk/client-sts';
 import { GetCallerIdentityCommand } from '@aws-sdk/client-sts';
 import type { AwsCredentialIdentity } from '@aws-sdk/types';
 import type { UserAgent } from '@smithy/types';
-import type { CredentialsClient } from './CredentialsClient';
 
 const MAX_TAG_VALUE_LENGTH = 256;
 const SANITIZATION_CHARACTER = '_';
@@ -282,19 +281,6 @@ export function isDefined<T>(i: T | undefined | null): i is T {
 }
 /* c8 ignore stop */
 
-export async function areCredentialsValid(credentialsClient: CredentialsClient) {
-  const client = credentialsClient.stsClient;
-  try {
-    const identity = await client.send(new GetCallerIdentityCommand({}));
-    if (identity.Account) {
-      return true;
-    }
-    return false;
-  } catch (_) {
-    return false;
-  }
-}
-
 /**
  * Like core.getBooleanInput, but respects the required option.
  *

src/index.ts

@@ -3,12 +3,12 @@ import type { AssumeRoleCommandOutput } from '@aws-sdk/client-sts';
 import { assumeRole } from './assumeRole';
 import { CredentialsClient } from './CredentialsClient';
 import {
-  areCredentialsValid,
   errorMessage,
   exportAccountId,
   exportCredentials,
   exportRegion,
   getBooleanInput,
+  getCallerIdentity,
   retryAndBackoff,
   toCredentialIdentity,
   translateEnvVariables,
@@ -53,8 +53,8 @@ export async function run() {
     });
     const roleChaining = getBooleanInput('role-chaining', { required: false });
     const outputCredentials = getBooleanInput('output-credentials', { required: false });
-    // Default to always outputting environment credentials unless profile is specified. If profile is specified, default
+    // Default to always outputting environment credentials unless profile is specified. If profile is specified,
-    // to no environment credentials (but still output them if the user specifically requests it).
+    // default to no environment credentials (but still output them if the user specifically requests it).
     const outputEnvCredentials = getBooleanInput('output-env-credentials', { required: false, default: !awsProfile });
     const unsetCurrentCredentials = getBooleanInput('unset-current-credentials', { required: false });
     let disableRetry = getBooleanInput('disable-retry', { required: false });
@@ -165,8 +165,16 @@ export async function run() {
 
     //if the user wants to attempt to use existing credentials, check if we have some already
     if (useExistingCredentials) {
-      const validCredentials = await areCredentialsValid(credentialsClient);
+      const identity = await (async () => {
-      if (validCredentials) {
+        try {
+          return await getCallerIdentity(credentialsClient.stsClient);
+        } catch {
+          return null;
+        }
+      })();
+      if (identity) {
+        // The allowed-account-ids guardrail applies to reused credentials too.
+        validateAccountId(expectedAccountIds, identity.Account);
         core.notice('Pre-existing credentials are valid. No need to generate new ones.');
         if (timeoutId) clearTimeout(timeoutId);
         return;

test/index.test.ts

@@ -1015,6 +1015,33 @@ describe('Configure AWS Credentials', {}, () => {
       await run();
       expect(core.setFailed).not.toHaveBeenCalled();
     });
+
+    it('fails on the use-existing-credentials path when the account is not allowed', async () => {
+      vi.mocked(core.getInput).mockImplementation(
+        mocks.getInput({
+          ...mocks.USE_EXISTING_CREDENTIALS_INPUTS,
+          'allowed-account-ids': '999999999999',
+        }),
+      );
+      mockedSTSClient.on(GetCallerIdentityCommand).resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
+
+      await run();
+      expect(core.setFailed).toHaveBeenCalledWith(expect.stringContaining('does not match'));
+    });
+
+    it('reuses existing credentials when their account is allowed', async () => {
+      vi.mocked(core.getInput).mockImplementation(
+        mocks.getInput({
+          ...mocks.USE_EXISTING_CREDENTIALS_INPUTS,
+          'allowed-account-ids': '111111111111',
+        }),
+      );
+      mockedSTSClient.on(GetCallerIdentityCommand).resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
+
+      await run();
+      expect(core.notice).toHaveBeenCalledWith('Pre-existing credentials are valid. No need to generate new ones.');
+      expect(core.setFailed).not.toHaveBeenCalled();
+    });
   });
 
   describe('Global Timeout Configuration', {}, () => {