Fixes #12 don't require region w/ instance principals

[jhorwit2]

No description provided.

[jhorwit2]

@harveylowndes the default logic sets the region information aka the region_key. IMO, the validation logic is a little too strict but i don't want to fix that here. There's no reason to fail hard if non-instance principal configuration is present; warnings suffice IMO.

[harveylowndes]

@jhorwit2 I did open a PR which contained a commit to skip setting defaults if instance principals were used e7e5ad4. I wonder if it's worth skipping validation completely if instance principals are used and not allowing the user to override the auth config credentials?

I agree however that warning over hard fail should be preferred.

[owainlewis]

Needs rebase. Since we're throwing away the auth credentials when instance principals are used, validating them doesn't serve any purpose so we could just skip.

[owainlewis]

Needs rebase or closing.