feat: allow-list option for aws account id

Users may set the `allowed-account-ids` input variable to define a
comma-separated list of accounts that may be authenticated against.

Resolves aws-actions#432

README.md

@@ -79,6 +79,17 @@ We recommend following [Amazon IAM best practices](https://docs.aws.amazon.com/I
 * [Grant least privilege](https://docs.aws.amazon.com/IAM/latest/UserGuide/best-practices.html#grant-least-privilege) to the credentials used in GitHub Actions workflows.  Grant only the permissions required to perform the actions in your GitHub Actions workflows.
 * [Monitor the activity](https://docs.aws.amazon.com/IAM/latest/UserGuide/best-practices.html#keep-a-log) of the credentials used in GitHub Actions workflows.
 
+To prevent accidental deploys to the incorrect environment, you may define a comma-separated list of allowed account IDs to configure credentials for:
+
+```yaml
+- name: Configure AWS Credentials
+  uses: aws-actions/configure-aws-credentials@v1
+  with:
+    role-to-assume: arn:aws:iam::123456789100:role/my-github-actions-role
+    aws-region: us-east-2
+    allowed-account-ids: 123456789100
+```
+
 ## Assuming a Role
 We recommend using [GitHub's OIDC provider](https://docs.github.com/en/actions/deployment/security-hardening-your-deployments/configuring-openid-connect-in-amazon-web-services) to get short-lived credentials needed for your actions. 
 Specifying `role-to-assume` **without** providing an `aws-access-key-id` or a `web-identity-token-file` will signal to the action that you wish to use the OIDC provider.

action.yml

@@ -55,8 +55,10 @@ inputs:
   role-skip-session-tagging:
     description: 'Skip session tagging during role assumption'
     required: false
-  http-proxy:
-    description: 'Proxy to use for the AWS SDK agent'
+  allowed-account-ids:
+    description: >-
+      Comma-separated list of allowed AWS account IDs to prevent accidental
+      deploys to the wrong environment.
     required: false
 outputs:
   aws-account-id:

index.js

@@ -15,6 +15,7 @@ const MAX_TAG_VALUE_LENGTH = 256;
 const SANITIZATION_CHARACTER = '_';
 const ROLE_SESSION_NAME = 'GitHubActions';
 const REGION_REGEX = /^[a-z0-9-]+$/g;
+const ACCOUNT_ID_LIST_REGEX = /^\d{12}(,\s?\d{12})*$/
 
 async function assumeRole(params) {
   // Assume a role to get short-lived credentials using longer-lived credentials.
@@ -300,13 +301,22 @@ async function run() {
     const roleSkipSessionTagging = roleSkipSessionTaggingInput.toLowerCase() === 'true';
     const webIdentityTokenFile = core.getInput('web-identity-token-file', { required: false });
     const proxyServer = core.getInput('http-proxy', { required: false });
+    const allowedAccountIds = core.getInput('allowed-account-ids', { required: false });
 
     if (!region.match(REGION_REGEX)) {
       throw new Error(`Region is not valid: ${region}`);
     }
 
     exportRegion(region);
 
+    if (allowedAccountIds && !allowedAccountIds.match(ACCOUNT_ID_LIST_REGEX)) {
+      let errorMessage = "Allowed account ID list is not valid, must be comma-separated list of 12-digit IDs";
+      if (maskAccountId.toLowerCase() == "false") {
+        errorMessage += `: ${allowedAccountIds}`;
+      }
+      throw new Error(errorMessage);
+    }
+
     // This wraps the logic for deciding if we should rely on the GH OIDC provider since we may need to reference
     // the decision in a few differennt places. Consolidating it here makes the logic clearer elsewhere.
     const useGitHubOIDCProvider = () => {
@@ -375,7 +385,20 @@ async function run() {
       if (!process.env.GITHUB_ACTIONS || accessKeyId) {
         await validateCredentials(roleCredentials.accessKeyId);
       }
-      await exportAccountId(maskAccountId, region);
+      sourceAccountId = await exportAccountId(maskAccountId, region);
+    }
+
+    // Check if configured account ID is in the provided allow-list
+    if (allowedAccountIds) {
+      // Convert string to a list and trim whitespace.
+      const accountIdList = allowedAccountIds.split(",").map((id) => id.trim());
+      if (!accountIdList.includes(sourceAccountId)) {
+        let errorMessage = "Account ID of the provided credentials is not in 'allowed-account-ids'";
+        if (maskAccountId.toLowerCase() == "false") {
+          errorMessage += `: ${sourceAccountId}`;
+        }
+        throw new Error(errorMessage);
+      }
     }
   }
   catch (error) {

index.test.js

@@ -809,6 +809,37 @@ describe('Configure AWS Credentials', () => {
 
         await run();
     });
+
+    test('denies accounts not defined in allow-account-ids', async () => {
+        process.env.SHOW_STACK_TRACE = 'false';
+
+        core.getInput = jest
+        .fn()
+        .mockImplementation(mockGetInput({ ...DEFAULT_INPUTS, 'allowed-account-ids': '000000000000' }));
+
+        await run();
+        expect(core.setFailed).toHaveBeenCalledWith(`Account ID of the provided credentials is not in 'allowed-account-ids'`);
+    });
+
+    test('allows accounts defined in allow-account-ids', async () => {
+        core.getInput = jest
+        .fn()
+        .mockImplementation(mockGetInput({ ...DEFAULT_INPUTS, 'allowed-account-ids': `${FAKE_ACCOUNT_ID}, 000000000000` }));
+
+        await run();
+    });
+
+    test('throws if account id list is invalid', async () => {
+        process.env.SHOW_STACK_TRACE = 'false';
+
+        // account id is too short
+        core.getInput = jest
+        .fn()
+        .mockImplementation(mockGetInput({ ...DEFAULT_INPUTS, 'allowed-account-ids': '0' }));
+
+        await run();
+        expect(core.setFailed).toHaveBeenCalledWith('Allowed account ID list is not valid, must be comma-separated list of 12-digit IDs');
+    })
 
     describe('proxy settings', () => {