fnando/env_vars

<!--
If you're making a doc PR or something tiny where the below is irrelevant,
delete this template and use a short description, but in your description aim to
include both what the change is, and why it is being made, with enough context
for anyone to understand.
-->

<details>
  <summary>PR Checklist</summary>

### PR Structure

- [ ] This PR has reasonably narrow scope (if not, break it down into smaller
      PRs).
- [ ] This PR avoids mixing refactoring changes with feature changes (split into
      two PRs otherwise).
- [ ] This PR's title starts is concise and descriptive.

### Thoroughness

- [ ] This PR adds tests for the most critical parts of the new functionality or
      fixes.
- [ ] I've updated any docs, `.md` files, etc… affected by this change.

</details>

### What

[TODO: Short statement about what is changing.]

### Why

[TODO: Why this change is being made. Include any context required to understand
the why.]

### Known limitations

[TODO or N/A]