feat(elbv2): add dropInvalidHeaderFields for elbv2 (#22466)

Dropping invalid HTTP headers is recommended and also appears in Security Hub controls as [ELB.4](https://docs.aws.amazon.com/securityhub/latest/userguide/securityhub-standards-fsbp-controls.html#fsbp-elb-4)

Attribute document: 
https://docs.aws.amazon.com/elasticloadbalancing/latest/APIReference/API_LoadBalancerAttribute.html

----

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Author: clueleaf

packages/@aws-cdk/aws-elasticloadbalancingv2/lib/alb/application-load-balancer.ts

@@ -43,6 +43,14 @@ export interface ApplicationLoadBalancerProps extends BaseLoadBalancerProps {
    * @default 60
    */
   readonly idleTimeout?: Duration;
+
+  /**
+   * Indicates whether HTTP headers with invalid header fields are removed
+   * by the load balancer (true) or routed to targets (false)
+   *
+   * @default false
+   */
+  readonly dropInvalidHeaderFields?: boolean;
 }
 
 /**
@@ -100,6 +108,7 @@ export class ApplicationLoadBalancer extends BaseLoadBalancer implements IApplic
 
     if (props.http2Enabled === false) { this.setAttribute('routing.http2.enabled', 'false'); }
     if (props.idleTimeout !== undefined) { this.setAttribute('idle_timeout.timeout_seconds', props.idleTimeout.toSeconds().toString()); }
+    if (props.dropInvalidHeaderFields) {this.setAttribute('routing.http.drop_invalid_header_fields.enabled', 'true'); }
   }
 
   /**

packages/@aws-cdk/aws-elasticloadbalancingv2/test/alb/load-balancer.test.ts

@@ -81,6 +81,7 @@ describe('tests', () => {
       deletionProtection: true,
       http2Enabled: false,
       idleTimeout: cdk.Duration.seconds(1000),
+      dropInvalidHeaderFields: true,
     });
 
     // THEN
@@ -98,6 +99,10 @@ describe('tests', () => {
           Key: 'idle_timeout.timeout_seconds',
           Value: '1000',
         },
+        {
+          Key: 'routing.http.drop_invalid_header_fields.enabled',
+          Value: 'true',
+        },
       ],
     });
   });