Fix some lints and remove panic in auth action

[adam-cattermole]

Only a couple minor changes:

• Move the logic for FailureMode resolution into a resolve_failure_mode function to reduce duplication
• Remove the 4 panics in the auth_action and, ignoring FailureMode, warn and return an InternalServerError
  • Currently these fields are NOT POPULATED by authorino (so these branches won't be hit under usual conditions) and would indicate the CheckResponse has been tampered with; that being said we don't want to panic and potentially end up denying legitimate requests