add option to include cloudfront arn

Author: jsalszbrun

_variables.tf

@@ -3,6 +3,11 @@ variable "name" {
   type        = string
 }
 
+variable "cloudfront_web_acl_id" {
+  default     = ""
+  description = "Optional web acl (WAF) to attach to CloudFront"
+}
+
 variable "hostnames" {
   description = "Hostnames to create DNS record for this app that the cloudfront distribution will accept"
   type        = list(string)

cloudfront.tf

@@ -13,7 +13,7 @@ resource "aws_cloudfront_distribution" "default" {
 
   depends_on = [aws_wafv2_web_acl.waf_cloudfront]
 
-  web_acl_id = var.waf_cloudfront_enable ? aws_wafv2_web_acl.waf_cloudfront[0].arn : null
+  web_acl_id = var.waf_cloudfront_enable ? (var.cloudfront_web_acl_id != null ? var.cloudfront_web_acl_id : aws_wafv2_web_acl.waf_cloudfront[0].arn) : null
 
   origin {
     domain_name = var.alb_dns_name