title: Vagrant source value from environmental variable
body: <p>I am setting up a vagrant deployment with aws as the backend. I would like to source values from the shell. For instance</p>
  
  <pre><code>Vagrant.configure("2") do |config|
    config.vm.box = "dummy"
  
    config.vm.provider :aws do |aws, override|
      aws.access_key_id = "YOUR KEY"
      aws.secret_access_key = "YOUR SECRET KEY"
      aws.session_token = "SESSION TOKEN"
      aws.keypair_name = "KEYPAIR NAME"
  
      aws.ami = "ami-7747d01e"
  
      override.ssh.username = "ubuntu"
      override.ssh.private_key_path = "PATH TO YOUR PRIVATE KEY"
    end
  end
  </code></pre>
  
  <p>I would like to populate the aws.{access_key_id,secret_access_key,etc} values from local environmental variables in BASH (e.g. $access_key_id, $secret_access_key, etc). </p>
  
  <p>Is this possible to do directly in ruby or is there a specific vagrant DSL technique that allows for this?</p>