fix(elasticache-alpha): the default engine for NoPasswordUser contradict in the docs

packages/@aws-cdk/aws-elasticache-alpha/README.md

@@ -305,6 +305,8 @@ const user = new elasticache.NoPasswordUser(this, 'User', {
 });
 ```
 
+> NOTE: `NoPasswordUser` is only available for Redis Cache.
+
 ### Default user
 
 ElastiCache automatically creates a default user with both a user ID and username set to `default`. This default user cannot be modified or deleted. The user is created as a no password authentication user.

packages/@aws-cdk/aws-elasticache-alpha/lib/no-password-user.ts

@@ -8,6 +8,11 @@ import { UserBase, UserBaseProps } from './user-base';
 
 const ELASTICACHE_NOPASSWORDUSER_SYMBOL = Symbol.for('@aws-cdk/aws-elasticache.NoPasswordUser');
 
+/**
+ * List of engines that support no-password authentication.
+ */
+const SUPPORTED_NO_PASSWORD_ENGINES = [UserEngine.REDIS];
+
 /**
  * Properties for defining an ElastiCache user with no password authentication.
  */
@@ -86,8 +91,8 @@ export class NoPasswordUser extends UserBase {
     this.userName = props.userName ?? props.userId;
     this.accessString = props.accessControl.accessString;
 
-    if (this.engine === UserEngine.VALKEY) {
-      throw new ValidationError('Valkey engine does not support no-password authentication.', this);
+    if (!SUPPORTED_NO_PASSWORD_ENGINES.includes(this.engine)) {
+      throw new ValidationError(`Engine '${this.engine}' does not support no-password authentication. Supported engines: ${SUPPORTED_NO_PASSWORD_ENGINES.join(', ')}.`, this);
     }
 
     this.resource = new CfnUser(this, 'Resource', {

packages/@aws-cdk/aws-elasticache-alpha/lib/user-base.ts

@@ -44,7 +44,7 @@ export interface UserBaseProps {
    * The engine type for the user.
    * Enum options: UserEngine.VALKEY, UserEngine.REDIS.
    *
-   * @default UserEngine.VALKEY.
+   * @default - UserEngine.REDIS for NoPasswordUser, UserEngine.VALKEY for all other user types.
    */
   readonly engine?: UserEngine;
   /**

packages/@aws-cdk/aws-elasticache-alpha/test/no-password-user.test.ts

@@ -14,7 +14,7 @@ describe('NoPasswordUser', () => {
         userId: 'test-user',
         engine: UserEngine.VALKEY,
         accessControl: AccessControl.fromAccessString('on ~* +@all'),
-      })).toThrow('Valkey engine does not support no-password authentication.');
+      })).toThrow("Engine 'valkey' does not support no-password authentication. Supported engines: redis.");
     });
   });