fix(s3): logging bucket blocks KMS_MANAGED encryption (#23514)

----
closes #23513

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

Author: biffgaut

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

@@ -2104,12 +2104,14 @@ export class Bucket extends BucketBase {
     if (!props.serverAccessLogsBucket && !props.serverAccessLogsPrefix) {
       return undefined;
     }
+
     if (
-      // The current bucket is being used and is configured for default SSE-KMS
-      !props.serverAccessLogsBucket && (
+      // KMS can't be used for logging since the logging service can't use the key - logs don't write
+      // KMS_MANAGED can't be used for logging since the account can't access the logging service key - account can't read logs
+      (!props.serverAccessLogsBucket && (
         props.encryptionKey ||
-        props.encryption === BucketEncryption.KMS ||
-        props.encryption === BucketEncryption.KMS_MANAGED) ||
+        props.encryption === BucketEncryption.KMS_MANAGED ||
+        props.encryption === BucketEncryption.KMS )) ||
       // Another bucket is being used that is configured for default SSE-KMS
       props.serverAccessLogsBucket?.encryptionKey
     ) {

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

@@ -338,26 +338,101 @@ describe('bucket', () => {
 
   });
 
-  test('throws error if using KMS-Managed key and server access logging to self', () => {
+  test('logs to self, no encryption does not throw error', () => {
+    const stack = new cdk.Stack();
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { encryption: s3.BucketEncryption.UNENCRYPTED, serverAccessLogsPrefix: 'test' });
+    }).not.toThrowError();
+  });
+
+  test('logs to self, S3 encryption does not throw error', () => {
+    const stack = new cdk.Stack();
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { encryption: s3.BucketEncryption.S3_MANAGED, serverAccessLogsPrefix: 'test' });
+    }).not.toThrowError();
+  });
+
+  test('logs to self, KMS_MANAGED encryption throws error', () => {
     const stack = new cdk.Stack();
     expect(() => {
       new s3.Bucket(stack, 'MyBucket', { encryption: s3.BucketEncryption.KMS_MANAGED, serverAccessLogsPrefix: 'test' });
-    }).toThrow('SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets');
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
+  });
+
+  test('logs to self, KMS encryption without key throws error', () => {
+    const stack = new cdk.Stack();
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { encryption: s3.BucketEncryption.KMS, serverAccessLogsPrefix: 'test' });
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
+  });
+
+  test('logs to self, KMS encryption with key throws error', () => {
+    const stack = new cdk.Stack();
+    const key = new kms.Key(stack, 'TestKey');
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { encryptionKey: key, encryption: s3.BucketEncryption.KMS, serverAccessLogsPrefix: 'test' });
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
   });
-  test('throws error if using KMS CMK and server access logging to self', () => {
+
+  test('logs to self, KMS key with no specific encryption specified throws error', () => {
     const stack = new cdk.Stack();
     const key = new kms.Key(stack, 'TestKey');
     expect(() => {
       new s3.Bucket(stack, 'MyBucket', { encryptionKey: key, serverAccessLogsPrefix: 'test' });
-    }).toThrow('SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets');
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
+  });
+
+  test('logs to separate bucket, no encryption does not throw error', () => {
+    const stack = new cdk.Stack();
+    const logBucket = new s3.Bucket(stack, 'testLogBucket', { encryption: s3.BucketEncryption.UNENCRYPTED });
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { serverAccessLogsBucket: logBucket });
+    }).not.toThrowError();
+  });
+
+  test('logs to separate bucket, S3 encryption does not throw error', () => {
+    const stack = new cdk.Stack();
+    const logBucket = new s3.Bucket(stack, 'testLogBucket', { encryption: s3.BucketEncryption.S3_MANAGED });
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { serverAccessLogsBucket: logBucket });
+    }).not.toThrowError();
+  });
+
+  // When provided an external bucket (as an IBucket), we cannot detect KMS_MANAGED encryption. Since this
+  // check is impossible, we skip thist test.
+  // eslint-disable-next-line jest/no-disabled-tests
+  test.skip('logs to separate bucket, KMS_MANAGED encryption throws error', () => {
+    const stack = new cdk.Stack();
+    const logBucket = new s3.Bucket(stack, 'testLogBucket', { encryption: s3.BucketEncryption.KMS_MANAGED });
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { serverAccessLogsBucket: logBucket });
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
   });
-  test('throws error if enabling server access logging to bucket with SSE-KMS', () => {
+
+  test('logs to separate bucket, KMS encryption without key throws error', () => {
+    const stack = new cdk.Stack();
+    const logBucket = new s3.Bucket(stack, 'testLogBucket', { encryption: s3.BucketEncryption.KMS });
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { serverAccessLogsBucket: logBucket });
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
+  });
+
+  test('logs to separate bucket, KMS encryption with key throws error', () => {
+    const stack = new cdk.Stack();
+    const key = new kms.Key(stack, 'TestKey');
+    const logBucket = new s3.Bucket(stack, 'testLogBucket', { encryptionKey: key, encryption: s3.BucketEncryption.KMS });
+    expect(() => {
+      new s3.Bucket(stack, 'MyBucket', { serverAccessLogsBucket: logBucket });
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
+  });
+
+  test('logs to separate bucket, KMS key with no specific encryption specified throws error', () => {
     const stack = new cdk.Stack();
     const key = new kms.Key(stack, 'TestKey');
-    const targetBucket = new s3.Bucket(stack, 'TargetBucket', { encryptionKey: key } );
+    const logBucket = new s3.Bucket(stack, 'testLogBucket', { encryptionKey: key });
     expect(() => {
-      new s3.Bucket(stack, 'MyBucket', { serverAccessLogsBucket: targetBucket });
-    }).toThrow('SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets');
+      new s3.Bucket(stack, 'MyBucket', { serverAccessLogsBucket: logBucket });
+    }).toThrow(/SSE-S3 is the only supported default bucket encryption for Server Access Logging target buckets/);
   });
 
   test('bucket with versioning turned on', () => {