Draft: Adopt params.permit (and expect?) more broadly

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What does this MR do and why?

Issue #83 recommends using params.permit. I'm submitting this as a draft right now to solicit more feedback.

Further comments on the diffs.

Validation steps

All specs pass locally with this change. I interpret the issue to be a refactor, so the hope is that no specs would have to change throughout, as behavior should be the same.

/cc @leetickett-gitlab