fix(custom-resources): assumedRole from AwsCustomResource invocation …

…leaked to next execution (#15776)

Fixes #15425

Credit to @nicolai-shape for proposing the fix itself.

----

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

packages/@aws-cdk/custom-resources/lib/aws-custom-resource/runtime/index.ts

@@ -161,26 +161,26 @@ export async function handler(event: AWSLambda.CloudFormationCustomResourceEvent
 
     if (call) {
 
+      let credentials;
       if (call.assumedRoleArn) {
-
         const timestamp = (new Date()).getTime();
 
         const params = {
           RoleArn: call.assumedRoleArn,
           RoleSessionName: `${timestamp}-${physicalResourceId}`.substring(0, 64),
         };
 
-        AWS.config.credentials = new AWS.ChainableTemporaryCredentials({
+        credentials = new AWS.ChainableTemporaryCredentials({
           params: params,
         });
-
       }
 
       if (!Object.prototype.hasOwnProperty.call(AWS, call.service)) {
         throw Error(`Service ${call.service} does not exist in AWS SDK version ${AWS.VERSION}.`);
       }
       const awsService = new (AWS as any)[call.service]({
         apiVersion: call.apiVersion,
+        credentials: credentials,
         region: call.region,
       });
 

packages/@aws-cdk/custom-resources/test/aws-custom-resource/runtime/index.test.ts

@@ -0,0 +1,158 @@
+import * as AWS from 'aws-sdk';
+import { PhysicalResourceId } from '../../../lib';
+import { handler } from '../../../lib/aws-custom-resource/runtime/index';
+
+/* eslint-disable no-console */
+console.log = jest.fn();
+
+jest.mock('aws-sdk', () => {
+  return {
+    ...jest.requireActual('aws-sdk'),
+    SSM: jest.fn(() => {
+      return {
+        config: {
+          apiVersion: 'apiVersion',
+          region: 'eu-west-1',
+        },
+        getParameter: () => {
+          return {
+            promise: async () => {},
+          };
+        },
+      };
+    }),
+  };
+});
+
+jest.mock('https', () => {
+  return {
+    request: (_: any, callback: () => void) => {
+      return {
+        on: () => undefined,
+        write: () => true,
+        end: callback,
+      };
+    },
+  };
+});
+
+afterEach(() => {
+  jest.clearAllMocks();
+});
+
+test('SDK global credentials are never set', async () => {
+  // WHEN
+  await handler({
+    LogicalResourceId: 'logicalResourceId',
+    RequestId: 'requestId',
+    RequestType: 'Create',
+    ResponseURL: 'responseUrl',
+    ResourceProperties: {
+      Create: JSON.stringify({
+        action: 'getParameter',
+        assumedRoleArn: 'arn:aws:iam::123456789012:role/CoolRole',
+        parameters: {
+          Name: 'foo',
+        },
+        physicalResourceId: PhysicalResourceId.of('id'),
+        service: 'SSM',
+      }),
+      ServiceToken: 'serviceToken',
+    },
+    ResourceType: 'resourceType',
+    ServiceToken: 'serviceToken',
+    StackId: 'stackId',
+  }, {} as AWSLambda.Context);
+
+  // THEN
+  expect(AWS.config).toBeInstanceOf(AWS.Config);
+  expect(AWS.config.credentials).toBeNull();
+});
+
+test('SDK credentials are not persisted across subsequent invocations', async () => {
+  // GIVEN
+  const mockCreds = new AWS.ChainableTemporaryCredentials();
+  jest.spyOn(AWS, 'ChainableTemporaryCredentials').mockReturnValue(mockCreds);
+
+  // WHEN
+  await handler({
+    LogicalResourceId: 'logicalResourceId',
+    RequestId: 'requestId',
+    RequestType: 'Create',
+    ResponseURL: 'responseUrl',
+    ResourceProperties: {
+      Create: JSON.stringify({
+        action: 'getParameter',
+        parameters: {
+          Name: 'foo',
+        },
+        physicalResourceId: PhysicalResourceId.of('id'),
+        service: 'SSM',
+      }),
+      ServiceToken: 'serviceToken',
+    },
+    ResourceType: 'resourceType',
+    ServiceToken: 'serviceToken',
+    StackId: 'stackId',
+  }, {} as AWSLambda.Context);
+
+  await handler({
+    LogicalResourceId: 'logicalResourceId',
+    RequestId: 'requestId',
+    RequestType: 'Create',
+    ResponseURL: 'responseUrl',
+    ResourceProperties: {
+      Create: JSON.stringify({
+        action: 'getParameter',
+        assumedRoleArn: 'arn:aws:iam::123456789012:role/CoolRole',
+        parameters: {
+          Name: 'foo',
+        },
+        physicalResourceId: PhysicalResourceId.of('id'),
+        service: 'SSM',
+      }),
+      ServiceToken: 'serviceToken',
+    },
+    ResourceType: 'resourceType',
+    ServiceToken: 'serviceToken',
+    StackId: 'stackId',
+  }, {} as AWSLambda.Context);
+
+  await handler({
+    LogicalResourceId: 'logicalResourceId',
+    RequestId: 'requestId',
+    RequestType: 'Create',
+    ResponseURL: 'responseUrl',
+    ResourceProperties: {
+      Create: JSON.stringify({
+        action: 'getParameter',
+        parameters: {
+          Name: 'foo',
+        },
+        physicalResourceId: PhysicalResourceId.of('id'),
+        service: 'SSM',
+      }),
+      ServiceToken: 'serviceToken',
+    },
+    ResourceType: 'resourceType',
+    ServiceToken: 'serviceToken',
+    StackId: 'stackId',
+  }, {} as AWSLambda.Context);
+
+  // THEN
+  expect(AWS.SSM).toHaveBeenNthCalledWith(1, {
+    apiVersion: undefined,
+    credentials: undefined,
+    region: undefined,
+  });
+  expect(AWS.SSM).toHaveBeenNthCalledWith(2, {
+    apiVersion: undefined,
+    credentials: mockCreds,
+    region: undefined,
+  });
+  expect(AWS.SSM).toHaveBeenNthCalledWith(3, {
+    apiVersion: undefined,
+    credentials: undefined,
+    region: undefined,
+  });
+});