feat(apigateway): support imported roles for integrations (aws#3369)

* feat(apigateway): support imported roles for intgrations

Change type of `IntegrationOptions.credentialsRole` to `IRole` to enable
using an imported role.

Fixes aws#2860

* make `Integration.props` internal

Since this is read only by `Method`.

This is technically a breaking change, but props is not part of the expected API.

allowed-breaking-changes.txt

@@ -7,3 +7,8 @@ incompatible-argument:@aws-cdk/aws-ecs.TaskDefinition.addVolume
 change-return-type:@aws-cdk/core.Fn.getAtt
 new-argument:@aws-cdk/aws-iam.ManagedPolicy.<initializer>
 new-argument:@aws-cdk/aws-iam.ManagedPolicy.<initializer>
+removed:@aws-cdk/aws-apigateway.AwsIntegration.props
+removed:@aws-cdk/aws-apigateway.HttpIntegration.props
+removed:@aws-cdk/aws-apigateway.Integration.props
+removed:@aws-cdk/aws-apigateway.LambdaIntegration.props
+removed:@aws-cdk/aws-apigateway.MockIntegration.props

packages/@aws-cdk/aws-apigateway/lib/integration.ts

@@ -31,7 +31,7 @@ export interface IntegrationOptions {
    *
    * @default A role is not assumed
    */
-  readonly credentialsRole?: iam.Role;
+  readonly credentialsRole?: iam.IRole;
 
   /**
    * Requires that the caller's identity be passed through from the request.
@@ -139,7 +139,16 @@ export interface IntegrationProps {
  * or implement on your own by specifying the set of props.
  */
 export class Integration {
-  constructor(readonly props: IntegrationProps) { }
+  constructor(private readonly props: IntegrationProps) { }
+
+  /**
+   * Allows `Method` to access the integration props.
+   *
+   * @internal
+   */
+  public get _props() {
+    return this.props;
+  }
 
   /**
    * Can be overridden by subclasses to allow the integration to interact with the method

packages/@aws-cdk/aws-apigateway/lib/method.ts

@@ -188,7 +188,7 @@ export class Method extends Resource {
 
     integration.bind(this);
 
-    const options = integration.props.options || { };
+    const options = integration._props.options || { };
 
     let credentials;
     if (options.credentialsPassthrough !== undefined && options.credentialsRole !== undefined) {
@@ -212,12 +212,12 @@ export class Method extends Resource {
     }
 
     return {
-      type: integration.props.type,
-      uri: integration.props.uri,
+      type: integration._props.type,
+      uri: integration._props.uri,
       cacheKeyParameters: options.cacheKeyParameters,
       cacheNamespace: options.cacheNamespace,
       contentHandling: options.contentHandling,
-      integrationHttpMethod: integration.props.integrationHttpMethod,
+      integrationHttpMethod: integration._props.integrationHttpMethod,
       requestParameters: options.requestParameters,
       requestTemplates: options.requestTemplates,
       passthroughBehavior: options.passthroughBehavior,