title: Cloudformation: CommaDelimitedList of Cert ARNs for ListenerCertificate Resource
body: <p>I am trying to pass in a CommaDelimitedList to populate a List of Certs in a <code>AWS::ElasticLoadBalancingV2::ListenerCertificate</code> resource.</p>
  <p><strong>Error:</strong> Value of property Certificates must be a list of objects</p>
  <p>I tried a few formats, including the following:</p>
  <pre><code>Parameters:
    pAdditionalAlbListenerCertArns:
      Type: CommaDelimitedList
      Default: &quot;arn:someCert1, arnsomeCert2&quot;
      Description: enter list of the ACM Certificates (Arns)
  
  ## Resource Format 1 - I would think this way would work as the result is [thing1, thing2]
  Resources:
  rCertificatesList:
      Type: AWS::ElasticLoadBalancingV2::ListenerCertificate
      Properties:
        Certificates: ! Ref  pAdditionalAlbListenerCertArns
  
  ## Resource Format 2 - I know this should not work, because it's a single item trying to be populated by a list.
  Resources:
  rCertificatesList:
      Type: AWS::ElasticLoadBalancingV2::ListenerCertificate
      Properties:
        Certificates: 
          CertificateArn: ! Ref  pAdditionalAlbListenerCertArns
  </code></pre>
  <p>Apparently Cfn is not smart enough to prepend each item with <code>CertificateArn:</code>.</p>
  <p>I have also tried combinations of <code>!Split</code>, <code>!Sub</code>, and <code>!Join</code> which gave the same error. Currently I am having to key in the certs directly, which is not viable. While I could create individual parameters for each cert, or use a <code>!Select</code> to grab them out of the list, I don't know how many I will have in each environment (DEV/TEST/PROD).</p>
  <p>I know this works cleanly for things like security groups; am I missing something?</p>
  <p>Thanks in advance!</p>