Ensure AWS ELB has one listener configured to listen for HTTPs traffic

AWS ELB does not have any HTTPs listener enabled for external traffic. In-transit data may be prone to MiTM attacks.

In AWS Console -

1. Sign in to the AWS Console and open the Load Balancer Console.
2. Choose the load balancer to edit and in the Actions drop down select Edit Listener.
3. Set the Load Balancer Protocol to HTTPS.
4. Select Change under the SSL Certificate and either enter the certificate details or choose one from ACM/IAM.
5. Select Save.

In Terraform -

1. In the aws_elb resource, set the listener.protocol to https.
2. Set the ssl_certificate_id to the ARN of the certificate to be used.

References:
https://docs.aws.amazon.com/elasticloadbalancing/latest/userguide/data-protection.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elb#lb_protocol