fix(cdk): allow bootstrap with policy names with a path (#26378)

Policy names with slashes (`/`) are not allowed when bootstrapping.

For example:
```
cdk bootstrap --custom-permissions-boundary aaa/bbb
```
Would fail:
```
Error: The permissions boundary name aaa/bbb does not match the IAM conventions.
```

This fix allows to specify paths in the policy name.

Closes #26320.

----

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

packages/@aws-cdk-testing/cli-integ/tests/cli-integ-tests/bootstrapping.integtest.ts

@@ -255,6 +255,17 @@ integTest('can use the custom permissions boundary to bootstrap', withoutBootstr
   expect(template).toContain('permission-boundary-name');
 }));
 
+integTest('can use the custom permissions boundary (with slashes) to bootstrap', withoutBootstrap(async (fixture) => {
+  let template = await fixture.cdkBootstrapModern({
+    // toolkitStackName doesn't matter for this particular invocation
+    toolkitStackName: fixture.bootstrapStackName,
+    showTemplate: true,
+    customPermissionsBoundary: 'permission-boundary-name/with/path',
+  });
+
+  expect(template).toContain('permission-boundary-name/with/path');
+}));
+
 integTest('can remove customPermissionsBoundary', withoutBootstrap(async (fixture) => {
   const bootstrapStackName = fixture.bootstrapStackName;
   const policyName = `${bootstrapStackName}-pb`;

packages/aws-cdk/lib/api/bootstrap/bootstrap-environment.ts

@@ -279,7 +279,9 @@ export class Bootstrapper {
 
   private validatePolicyName(permissionsBoundary: string) {
     // https://docs.aws.amazon.com/IAM/latest/APIReference/API_CreatePolicy.html
-    const regexp: RegExp = /[\w+=,.@-]+/;
+    // Added support for policy names with a path
+    // See https://github.com/aws/aws-cdk/issues/26320
+    const regexp: RegExp = /[\w+\/=,.@-]+/;
     const matches = regexp.exec(permissionsBoundary);
     if (!(matches && matches.length === 1 && matches[0] === permissionsBoundary)) {
       throw new Error(`The permissions boundary name ${permissionsBoundary} does not match the IAM conventions.`);

packages/aws-cdk/test/api/bootstrap2.test.ts

@@ -207,6 +207,28 @@ describe('Bootstrapping v2', () => {
     ]));
   });
 
+  test('adding permission boundary with path in policy name', async () => {
+    mockTheToolkitInfo({
+      Parameters: [
+        {
+          ParameterKey: 'InputPermissionsBoundary',
+          ParameterValue: '',
+        },
+      ],
+    });
+    await bootstrapper.bootstrapEnvironment(env, sdk, {
+      parameters: {
+        customPermissionsBoundary: 'permissions-boundary-name/with/path',
+      },
+    });
+
+    expect(stderrMock.mock.calls).toEqual(expect.arrayContaining([
+      expect.arrayContaining([
+        expect.stringMatching(/Adding new permissions boundary permissions-boundary-name\/with\/path/),
+      ]),
+    ]));
+  });
+
   test('passing trusted accounts without CFN managed policies results in an error', async () => {
     await expect(bootstrapper.bootstrapEnvironment(env, sdk, {
       parameters: {