Implement a Whitelist in Terraform

This happens sometimes that you need to implement a variable in Terraform, that can only take an acceptable list of values. In my case, it was a list of DNS names that needed to be accepted by a security team, and stored in a file on an S3.
The difficulty is to make the Terraform fail if you decide to use a bad value. There are several ways to do that, here is mine:

data "aws_s3_bucket_object" "white_list" {
  bucket = "my-bucket"
  key    = "my_white_list"
}

locals {
  value_to_check = "SomeValue"

  white_list = split(
    " ",
    replace(data.aws_s3_bucket_object.white_list.body, "/\\s+/", " "),
  )
  allowed = zipmap(local.white_list, local.white_list)[local.value_to_check]
}

The data part is fetching my file from an S3, but you can imagine using a simple file command, or even a hardcoded list.
Then I am setting the value to check, which is hardcoded here for the example, but it will typically be calculated or retrieved from some other place. I then create a Terraform list from the file, by removing any extra space and splitting the lines.
Finally, here is my way of making Terraform fail. I create a map from the white list, using the zipmap function, and get the value from it. If the value is not in the map, Terraform will just stop with an error.