Enable developers to fetch the list of attributes which the current user has access to

[jrschumacher]

To build PEPs with rich UX, developers need the ability to get the list of attributes that the user has access to. This feature enables PEPs to only allow creating TDFs with attributes to ensure the data created is accessible.

[jakedoublev]

Blocked by #644

[strantalis]

@jrschumacher @jakedoublev Is this just a get entitlements call to determine which attributes a user has access to?

[jakedoublev]

@jrschumacher @jakedoublev Is this just a get entitlements call to determine which attributes a user has access to?

@strantalis Yes, it is, but this issue implies an "unscoped" (no FQNs) GetEntitlements call, which will currently result in an error with the current Auth Service implementation.

The blocking issue (#644) will allow the ability to go from Entity -> flattened Entity Representation selectors/values -> matched Subject Condition Sets / Mappings -> Attribute Values as Entitlements.

[strantalis]

@jakedoublev If scopes is empty we should just return all entitlements for a user. At least thats how I would expect it to work.

I don't fully understand why we error if scopes is empty. Do you know if we even did performance tests against this path?

[jrschumacher]

No I don't think we have with the latest.

[jrschumacher]

The performance concerns seem related to the algorithmic complexity, as documented in #365. However, we could allow it and just document that there might be performance issues with X number of subject mappings based on our performance tests.