Support access to Arches services as an authenticated user

[robgaston]

We will need to be able to access data in Arches as an authenticated user in order to access restricted business data.

One possibility would be to create a Koop authorization plugin that would use Arches authentication API on the backend

[apeters]

Looking at the Koop authorization plugin it looks like we could create a custom Koop auth plugin to handle this scenario. Unlike the built-in Koop-Auth-Direct-File plugin, we'd have make sure to pass the token all the way to the Arches endpoint. What we'd probably implement would be something similar to what we did for the mobile app.
It might preclude the use of a caching provider (caching would have to happen on a per/user basis).