feat(cognito): addDomain() on an imported user pool (#8123)

In addition, reduce code duplication by introducing an abstract
UserPoolBase class.

----

*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-cognito/lib/user-pool.ts

@@ -526,33 +526,52 @@ export interface IUserPool extends IResource {
   readonly userPoolArn: string;
 
   /**
-   * Create a user pool client.
+   * Add a new app client to this user pool.
+   * @see https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-client-apps.html
    */
   addClient(id: string, options?: UserPoolClientOptions): IUserPoolClient;
+
+  /**
+   * Associate a domain to this user pool.
+   * @see https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-pools-assign-domain.html
+   */
+  addDomain(id: string, options: UserPoolDomainOptions): UserPoolDomain;
+}
+
+abstract class UserPoolBase extends Resource implements IUserPool {
+  public abstract readonly userPoolId: string;
+  public abstract readonly userPoolArn: string;
+
+  public addClient(id: string, options?: UserPoolClientOptions): IUserPoolClient {
+    return new UserPoolClient(this, id, {
+      userPool: this,
+      ...options,
+    });
+  }
+
+  public addDomain(id: string, options: UserPoolDomainOptions): UserPoolDomain {
+    return new UserPoolDomain(this, id, {
+      userPool: this,
+      ...options,
+    });
+  }
 }
 
 /**
  * Define a Cognito User Pool
  */
-export class UserPool extends Resource implements IUserPool {
+export class UserPool extends UserPoolBase {
   /**
    * Import an existing user pool based on its id.
    */
   public static fromUserPoolId(scope: Construct, id: string, userPoolId: string): IUserPool {
-    class Import extends Resource implements IUserPool {
+    class Import extends UserPoolBase {
       public readonly userPoolId = userPoolId;
       public readonly userPoolArn = Stack.of(this).formatArn({
         service: 'cognito-idp',
         resource: 'userpool',
         resourceName: userPoolId,
       });
-
-      public addClient(clientId: string, options?: UserPoolClientOptions): IUserPoolClient {
-        return new UserPoolClient(this, clientId, {
-          userPool: this,
-          ...options,
-        });
-      }
     }
     return new Import(scope, id);
   }
@@ -669,28 +688,6 @@ export class UserPool extends Resource implements IUserPool {
     (this.triggers as any)[operation.operationName] = fn.functionArn;
   }
 
-  /**
-   * Add a new app client to this user pool.
-   * @see https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-client-apps.html
-   */
-  public addClient(id: string, options?: UserPoolClientOptions): IUserPoolClient {
-    return new UserPoolClient(this, id, {
-      userPool: this,
-      ...options,
-    });
-  }
-
-  /**
-   * Associate a domain to this user pool.
-   * @see https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-pools-assign-domain.html
-   */
-  public addDomain(id: string, options: UserPoolDomainOptions): UserPoolDomain {
-    return new UserPoolDomain(this, id, {
-      userPool: this,
-      ...options,
-    });
-  }
-
   private addLambdaPermission(fn: lambda.IFunction, name: string): void {
     const capitalize = name.charAt(0).toUpperCase() + name.slice(1);
     fn.addPermission(`${capitalize}Cognito`, {

packages/@aws-cdk/aws-cognito/test/user-pool.test.ts

@@ -818,6 +818,35 @@ test('addClient', () => {
   });
 });
 
+test('addDomain', () => {
+  // GIVEN
+  const stack = new Stack();
+
+  // WHEN
+  const userpool = new UserPool(stack, 'Pool');
+  userpool.addDomain('UserPoolDomain', {
+    cognitoDomain: {
+      domainPrefix: 'userpooldomain',
+    },
+  });
+  const imported = UserPool.fromUserPoolId(stack, 'imported', 'imported-userpool-id');
+  imported.addDomain('UserPoolImportedDomain', {
+    cognitoDomain: {
+      domainPrefix: 'userpoolimporteddomain',
+    },
+  });
+
+  // THEN
+  expect(stack).toHaveResourceLike('AWS::Cognito::UserPoolDomain', {
+    Domain: 'userpooldomain',
+    UserPoolId: stack.resolve(userpool.userPoolId),
+  });
+  expect(stack).toHaveResourceLike('AWS::Cognito::UserPoolDomain', {
+    Domain: 'userpoolimporteddomain',
+    UserPoolId: stack.resolve(imported.userPoolId),
+  });
+});
+
 function fooFunction(scope: Construct, name: string): lambda.IFunction {
   return new lambda.Function(scope, name, {
     functionName: name,