fix(cognito-identitypool-alpha): inconvenient IdentityPoolProviderUrl.userPool() (#29025)

### Reason for this change

`IdentityPoolProviderUrl.userPool()` requires a string `url` currently.
The description is "User Pool Provider Url".
It should be ``` `${userPool.userPoolProviderName}:${userPoolClient.userPoolClientId}` ```.

`UserPool` has an attribute `userPoolProviderUrl` which description is "User Pool Provider Url", but confusingly, it cannot be specified to `IdentityPoolProviderUrl.userPool()`.

The format of the identity provider identifier isn't well documented.
See [SetIdentityPoolRoles API reference](https://docs.aws.amazon.com/cognitoidentity/latest/APIReference/API_SetIdentityPoolRoles.html) for example of User Pool's identity provider identifier.

### Description of changes

This PR fixes `IdentityPoolProviderUrl.userPool()` to accept `UserPool` and `UserPoolClient` instead of a string `url`.
It generates a correct identifier described above.

### Description of how you validated changes

Existing integration test generates an identifier as described above.
The snapshot won't be changed by this PR.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

BREAKING CHANGE: The argument of `IdentityPoolProviderUrl.userPool()` has been changed from `url: string` to `userPool: UserPool, userPoolClient: UserPoolClient`. If you want to specify custom identifier string, use `IdentityPoolProviderUrl.custom()` instead.

----

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

Author: Tietew

packages/@aws-cdk/aws-cognito-identitypool-alpha/README.md

@@ -329,18 +329,14 @@ new IdentityPool(this, 'myidentitypool', {
 });
 ```
 
-For identity providers that don't have static Urls, a custom Url or User Pool Client Url can be supplied:
+For identity providers that don't have static Urls, a custom Url can be supplied:
 
 ```ts
 import { IdentityPoolProviderUrl } from '@aws-cdk/aws-cognito-identitypool-alpha';
 
 new IdentityPool(this, 'myidentitypool', {
   identityPoolName: 'myidentitypool',
   roleMappings: [
-    {
-      providerUrl: IdentityPoolProviderUrl.userPool('cognito-idp.my-idp-region.amazonaws.com/my-idp-region_abcdefghi:app_client_id'),
-      useToken: true,
-    },
     {
       providerUrl: IdentityPoolProviderUrl.custom('my-custom-provider.com'),
       useToken: true,
@@ -354,15 +350,16 @@ This is because by default, the key in the Cloudformation role mapping hash is t
 cannot be references. For example:
 
 ```ts
-import { UserPool } from 'aws-cdk-lib/aws-cognito';
+import { UserPool, UserPoolClient } from 'aws-cdk-lib/aws-cognito';
 import { IdentityPoolProviderUrl } from '@aws-cdk/aws-cognito-identitypool-alpha';
 
-declare const userPool : UserPool;
+declare const userPool: UserPool;
+declare const userPoolClient: UserPoolClient;
 new IdentityPool(this, 'myidentitypool', {
   identityPoolName: 'myidentitypool',
   roleMappings: [{
     mappingKey: 'cognito',
-    providerUrl: IdentityPoolProviderUrl.userPool(userPool.userPoolProviderUrl),
+    providerUrl: IdentityPoolProviderUrl.userPool(userPool, userPoolClient),
     useToken: true,
   }],
 });
@@ -399,4 +396,3 @@ IdentityPool.fromIdentityPoolId(this, 'my-imported-identity-pool',
 IdentityPool.fromIdentityPoolArn(this, 'my-imported-identity-pool',
   'arn:aws:cognito-identity:us-east-1:123456789012:identitypool/us-east-1:dj2823ryiwuhef937');
 ```
-

packages/@aws-cdk/aws-cognito-identitypool-alpha/lib/identitypool.ts

@@ -1,5 +1,7 @@
 import {
   CfnIdentityPool,
+  UserPool,
+  UserPoolClient,
 } from 'aws-cdk-lib/aws-cognito';
 import {
   IOpenIdConnectProvider,
@@ -155,7 +157,8 @@ export class IdentityPoolProviderUrl {
   }
 
   /** User Pool Provider Url */
-  public static userPool(url: string): IdentityPoolProviderUrl {
+  public static userPool(userPool: UserPool, userPoolClient: UserPoolClient): IdentityPoolProviderUrl {
+    const url = `${userPool.userPoolProviderName}:${userPoolClient.userPoolClientId}`;
     return new IdentityPoolProviderUrl(IdentityPoolProviderType.USER_POOL, url);
   }
 

packages/@aws-cdk/aws-cognito-identitypool-alpha/test/identitypool.test.ts

@@ -440,7 +440,7 @@ describe('role mappings', () => {
     const providerUrl = Fn.importValue('ProviderUrl');
     expect(() => new IdentityPool(stack, 'TestIdentityPoolRoleMappingErrors', {
       roleMappings: [{
-        providerUrl: IdentityPoolProviderUrl.userPool(providerUrl),
+        providerUrl: IdentityPoolProviderUrl.custom(providerUrl),
         useToken: true,
       }],
     })).toThrowError('mappingKey must be provided when providerUrl.value is a token');
@@ -452,7 +452,7 @@ describe('role mappings', () => {
     new IdentityPool(stack, 'TestIdentityPoolRoleMappingToken', {
       roleMappings: [{
         mappingKey: 'theKey',
-        providerUrl: IdentityPoolProviderUrl.userPool(providerUrl),
+        providerUrl: IdentityPoolProviderUrl.custom(providerUrl),
         useToken: true,
       }],
     });
@@ -532,6 +532,8 @@ describe('role mappings', () => {
 
   test('role mapping with rules configuration', () => {
     const stack = new Stack();
+    const pool = new UserPool(stack, 'Pool');
+    const client = pool.addClient('Client');
     const adminRole = new Role(stack, 'adminRole', {
       assumedBy: new ServicePrincipal('admin.amazonaws.com'),
     });
@@ -557,6 +559,11 @@ describe('role mappings', () => {
     });
     const idPool = new IdentityPool(stack, 'TestIdentityPoolRoleMappingRules', {
       roleMappings: [{
+        mappingKey: 'cognito',
+        providerUrl: IdentityPoolProviderUrl.userPool(pool, client),
+        useToken: true,
+      },
+      {
         providerUrl: IdentityPoolProviderUrl.AMAZON,
         resolveAmbiguousRoles: true,
         rules: [
@@ -601,6 +608,16 @@ describe('role mappings', () => {
         Ref: 'TestIdentityPoolRoleMappingRulesC8C07BC3',
       },
       RoleMappings: {
+        'cognito': {
+          IdentityProvider: {
+            'Fn::Join': ['', [
+              { 'Fn::GetAtt': ['PoolD3F588B8', 'ProviderName'] },
+              ':',
+              { Ref: 'PoolClient8A3E5EB7' },
+            ]],
+          },
+          Type: 'Token',
+        },
         'www.amazon.com': {
           AmbiguousRoleResolution: 'AuthenticatedRole',
           IdentityProvider: 'www.amazon.com',
@@ -696,4 +713,4 @@ describe('role mappings', () => {
       },
     });
   });
-});
+});

packages/@aws-cdk/aws-cognito-identitypool-alpha/test/integ.identitypool.ts

@@ -62,7 +62,7 @@ const idPool = new IdentityPool(stack, 'identitypool', {
   roleMappings: [
     {
       mappingKey: 'theKey',
-      providerUrl: IdentityPoolProviderUrl.userPool(`${userPool.userPoolProviderName}:${client.userPoolClientId}`),
+      providerUrl: IdentityPoolProviderUrl.userPool(userPool, client),
       useToken: true,
     },
   ],