fix(cli): format of tags in cdk.json is not validated (aws#21050)

If tags is present in cdk.json, validate that it is an array of objects, and each object has a Tag string and a Value string. If tags is not structurally valid `cdk bootstrap` and `cdk deploy` fail with an error.

`tags must be an array of { Tag: string, Value: string } objects`

There is no attempt to validate the strings of each Tag and Value beyond that they are strings.

closes aws#20854 

----

### All Submissions:

* [x] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md)

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/cli.ts

@@ -23,6 +23,7 @@ import { data, debug, error, print, setLogLevel, setCI } from '../lib/logging';
 import { displayNotices, refreshNotices } from '../lib/notices';
 import { Command, Configuration, Settings } from '../lib/settings';
 import * as version from '../lib/version';
+import { validateTags } from './util/tags';
 
 // https://github.com/yargs/yargs/issues/1929
 // https://github.com/evanw/esbuild/issues/1492
@@ -434,7 +435,7 @@ async function initCommandLine() {
           force: argv.force,
           toolkitStackName: toolkitStackName,
           execute: args.execute,
-          tags: configuration.settings.get(['tags']),
+          tags: validateTags(configuration.settings.get(['tags'])),
           terminationProtection: args.terminationProtection,
           parameters: {
             bucketName: configuration.settings.get(['toolkitBucket', 'bucketName']),
@@ -464,7 +465,7 @@ async function initCommandLine() {
           notificationArns: args.notificationArns,
           requireApproval: configuration.settings.get(['requireApproval']),
           reuseAssets: args['build-exclude'],
-          tags: configuration.settings.get(['tags']),
+          tags: validateTags(configuration.settings.get(['tags'])),
           execute: args.execute,
           changeSetName: args.changeSetName,
           force: args.force,

packages/aws-cdk/lib/util/tags.ts

@@ -0,0 +1,20 @@
+import { Tag } from '../cdk-toolkit';
+
+/**
+ * Throws an error if tags is neither undefined nor an array of Tags,
+ * as defined in cdk-toolkit.ts.
+ *
+ * It does not attempt to validate the tags themselves. It only validates
+ * that the objects in the array conform to the Tags interface.
+ */
+export function validateTags(tags: any): Tag[] | undefined {
+  const valid = tags === undefined || (
+    Array.isArray(tags) &&
+    tags.every(t => typeof(t.Tag) === 'string' && typeof(t.Value) === 'string')
+  );
+  if (valid) {
+    return tags;
+  } else {
+    throw new Error('tags must be an array of { Tag: string, Value: string } objects');
+  }
+}

packages/aws-cdk/test/util/tags.test.ts

@@ -0,0 +1,31 @@
+import { validateTags } from '../../lib/util/tags';
+
+test('validateTags does not throw when given undefined', () => {
+  expect(validateTags(undefined)).toBeUndefined();
+});
+
+test('validateTags does not throw when given an empty array', () => {
+  const tags: any = [];
+  expect(validateTags(tags)).toBe(tags);
+});
+
+test('validateTags does not throw when given array of Tag objects', () => {
+  const tags: any = [{ Tag: 'a', Value: 'b' }];
+  expect(validateTags(tags)).toBe(tags);
+});
+
+test('validateTags throws when given an object', () => {
+  expect(() => validateTags({ a: 'b' })).toThrow('tags must be');
+});
+
+test('validateTags throws when given an array of non-Tag objects', () => {
+  expect(() => validateTags([{ a: 'b' }])).toThrow('tags must be');
+});
+
+test('validateTags throws when Tag is not a string', () => {
+  expect(() => validateTags([{ Tag: null, Value: 'b' }])).toThrow();
+});
+
+test('validateTags throws when Value is not a string', () => {
+  expect(() => validateTags([{ Tag: 'a', Value: null }])).toThrow();
+});