title: Add variable to data
body: <p>Im trying to concatenate a data with variable (Terraform v0.12.0):</p>
  
  <pre><code>variable "my_var" {
      default = "secret_string"
  }
  
  auth_token = data.external.get_secret.result.var.my_var 
  </code></pre>
  
  <p>It's work in case of:</p>
  
  <p><code>auth_token = data.external.get_secret.result.secret_string</code> </p>
  
  <p>As I can see I can't to add variable to data. Do we have any workaround for this case? Thanks</p>