fix(s3): Bucket Key cannot be used with KMS_MANAGED key (#22331)

- BucketEncryption.KMS means: bring your own key.
- BucketEncryption.KMS_MANAGED means: use the AWS default key (which is free).

Bucket Key means "S3 uses a shadow key to reduce cost on encryption operations". It should apply to both KMS use cases, but was written to only apply to the BYOK scenario.

Also allow the other one.

----

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

packages/@aws-cdk/aws-s3/lib/bucket.ts

@@ -1354,10 +1354,15 @@ export interface BucketProps {
   readonly enforceSSL?: boolean;
 
   /**
-   * Specifies whether Amazon S3 should use an S3 Bucket Key with server-side
-   * encryption using KMS (SSE-KMS) for new objects in the bucket.
+   * Whether Amazon S3 should use its own intermediary key to generate data keys.
    *
-   * Only relevant, when Encryption is set to {@link BucketEncryption.KMS}
+   * Only relevant when using KMS for encryption.
+   *
+   * - If not enabled, every object GET and PUT will cause an API call to KMS (with the
+   *   attendant cost implications of that).
+   * - If enabled, S3 will use its own time-limited key instead.
+   *
+   * Only relevant, when Encryption is set to `BucketEncryption.KMS` or `BucketEncryption.KMS_MANAGED`.
    *
    * @default - false
    */
@@ -1943,7 +1948,7 @@ export class Bucket extends BucketBase {
     }
 
     // if bucketKeyEnabled is set, encryption must be set to KMS.
-    if (props.bucketKeyEnabled && encryptionType !== BucketEncryption.KMS) {
+    if (props.bucketKeyEnabled && ![BucketEncryption.KMS, BucketEncryption.KMS_MANAGED].includes(encryptionType)) {
       throw new Error(`bucketKeyEnabled is specified, so 'encryption' must be set to KMS (value: ${encryptionType})`);
     }
 
@@ -1983,7 +1988,10 @@ export class Bucket extends BucketBase {
     if (encryptionType === BucketEncryption.KMS_MANAGED) {
       const bucketEncryption = {
         serverSideEncryptionConfiguration: [
-          { serverSideEncryptionByDefault: { sseAlgorithm: 'aws:kms' } },
+          {
+            bucketKeyEnabled: props.bucketKeyEnabled,
+            serverSideEncryptionByDefault: { sseAlgorithm: 'aws:kms' },
+          },
         ],
       };
       return { bucketEncryption };
@@ -2288,17 +2296,17 @@ export enum BucketEncryption {
   /**
    * Objects in the bucket are not encrypted.
    */
-  UNENCRYPTED = 'NONE',
+  UNENCRYPTED = 'UNENCRYPTED',
 
   /**
    * Server-side KMS encryption with a master key managed by KMS.
    */
-  KMS_MANAGED = 'MANAGED',
+  KMS_MANAGED = 'KMS_MANAGED',
 
   /**
    * Server-side encryption with a master key managed by S3.
    */
-  S3_MANAGED = 'S3MANAGED',
+  S3_MANAGED = 'S3_MANAGED',
 
   /**
    * Server-side encryption with a KMS key managed by the user.

packages/@aws-cdk/aws-s3/test/bucket.test.ts

@@ -306,25 +306,19 @@ describe('bucket', () => {
     });
   });
 
-  test('bucketKeyEnabled can be enabled', () => {
+  test.each([s3.BucketEncryption.KMS, s3.BucketEncryption.KMS_MANAGED])('bucketKeyEnabled can be enabled with %p encryption', (encryption) => {
     const stack = new cdk.Stack();
 
-    new s3.Bucket(stack, 'MyBucket', { bucketKeyEnabled: true, encryption: s3.BucketEncryption.KMS });
+    new s3.Bucket(stack, 'MyBucket', { bucketKeyEnabled: true, encryption });
 
     Template.fromStack(stack).hasResourceProperties('AWS::S3::Bucket', {
       'BucketEncryption': {
         'ServerSideEncryptionConfiguration': [
           {
             'BucketKeyEnabled': true,
-            'ServerSideEncryptionByDefault': {
-              'KMSMasterKeyID': {
-                'Fn::GetAtt': [
-                  'MyBucketKeyC17130CF',
-                  'Arn',
-                ],
-              },
+            'ServerSideEncryptionByDefault': Match.objectLike({
               'SSEAlgorithm': 'aws:kms',
-            },
+            }),
           },
         ],
       },
@@ -336,10 +330,10 @@ describe('bucket', () => {
 
     expect(() => {
       new s3.Bucket(stack, 'MyBucket', { bucketKeyEnabled: true, encryption: s3.BucketEncryption.S3_MANAGED });
-    }).toThrow("bucketKeyEnabled is specified, so 'encryption' must be set to KMS (value: S3MANAGED)");
+    }).toThrow("bucketKeyEnabled is specified, so 'encryption' must be set to KMS (value: S3_MANAGED)");
     expect(() => {
       new s3.Bucket(stack, 'MyBucket3', { bucketKeyEnabled: true });
-    }).toThrow("bucketKeyEnabled is specified, so 'encryption' must be set to KMS (value: NONE)");
+    }).toThrow("bucketKeyEnabled is specified, so 'encryption' must be set to KMS (value: UNENCRYPTED)");
 
   });