feat(autoscaling): let AutoScalingGroup be IGrantable (#4654)

* feat(autoscaling): let AutoScalingGroup be IGrantable

* feat(autoscaling): let AutoScalingGroup be IGrantable

Author: abelmokadem

packages/@aws-cdk/aws-autoscaling/lib/auto-scaling-group.ts

@@ -348,7 +348,8 @@ export class AutoScalingGroup extends AutoScalingGroupBase implements
   elb.ILoadBalancerTarget,
   ec2.IConnectable,
   elbv2.IApplicationLoadBalancerTarget,
-  elbv2.INetworkLoadBalancerTarget {
+  elbv2.INetworkLoadBalancerTarget,
+  iam.IGrantable {
 
   public static fromAutoScalingGroupName(scope: Construct, id: string, autoScalingGroupName: string): IAutoScalingGroup {
     class Import extends AutoScalingGroupBase {
@@ -378,6 +379,11 @@ export class AutoScalingGroup extends AutoScalingGroupBase implements
    */
   public readonly role: iam.IRole;
 
+  /**
+   * The principal to grant permissions to
+   */
+  public readonly grantPrincipal: iam.IPrincipal;
+
   /**
    * Name of the AutoScalingGroup
    */
@@ -421,6 +427,8 @@ export class AutoScalingGroup extends AutoScalingGroupBase implements
       assumedBy: new iam.ServicePrincipal('ec2.amazonaws.com')
     });
 
+    this.grantPrincipal = this.role;
+
     const iamProfile = new iam.CfnInstanceProfile(this, 'InstanceProfile', {
       roles: [ this.role.roleName ]
     });