## Changes
This PR adds the auth.EnvVars function, which is a list of all
environment variables that the SDK uses to read auth configuration.
This is useful for spawning subprocesses since you can unset all auth
environment variables to clean up the environment before configuring the
auth.
It's used in #2278 today and will also be useful for the `databricks
bundle exec` command.
## Tests
Unit test.
## Changes
This PR adds a warning which gives users clear guidance when they try to
use variable interpolation for an auth field.
## Tests
Modify existing acceptance test.