fix(redshift): Fix Redshift User Secret Multi-User Rotation

Fixes Redshift User Secret Multi-User Rotation for new Users
by including `masterarn` in the Secret's Serialized JSON Object Text.

Note: This doesn't affect existing users (nor fixes roation for them)
since the secret string template is only used when the secret is
first created. For those existing secrets, the secret text will need
to be updated to include `masterarn` using the GetSecretValue and
UpdateSecret SecretManager APIs.

closes #28852

----

*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-redshift-alpha/lib/database-secret.ts

@@ -17,6 +17,13 @@ export interface DatabaseSecretProps {
    * @default default master key
    */
   readonly encryptionKey?: kms.IKey;
+
+  /**
+   * The master secret which will be used to rotate this secret.
+   *
+   * @default - no master secret information will be included
+   */
+  readonly masterSecret?: secretsmanager.ISecret;
 }
 
 /**
@@ -30,10 +37,13 @@ export class DatabaseSecret extends secretsmanager.Secret {
       encryptionKey: props.encryptionKey,
       generateSecretString: {
         passwordLength: 30, // Redshift password could be up to 64 characters
-        secretStringTemplate: JSON.stringify({ username: props.username }),
+        secretStringTemplate: JSON.stringify({
+          username: props.username,
+          masterarn: props.masterSecret?.secretArn,
+        }),
         generateStringKey: 'password',
         excludeCharacters: '"@/\\\ \'',
       },
     });
   }
-}
+}

packages/@aws-cdk/aws-redshift-alpha/lib/user.ts

@@ -153,6 +153,7 @@ export class User extends UserBase {
     const secret = new DatabaseSecret(this, 'Secret', {
       username,
       encryptionKey: props.encryptionKey,
+      masterSecret: props.adminUser,
     });
     const attachedSecret = secret.attach(props.cluster);
     this.password = attachedSecret.secretValueFromJson('password');