[keycloak-user] Question about CBAC + Pushing Claims + Authorization Scopes

[Álvaro Gómez]

Hi,

We are applying RBAC and CBAC models to evaluate permissions in a
multi-tenant UMA application. We are using Pushing Claims to let custom
policies determine if an user has an specific role in a provided context
(tenant) via Pushing Claims.

Everything works fine if we use non-scoped resources but things get a bit
confusing when we use scoped ones since the pushing-claims (representing
the tenants) end up mixed in the RPT permission claim without leaving any
trace of the scopes with which they were pushed along. Consider the
following example:

We have an application which manages products (represented by resources).
There are profiles (represented by roles) which allow users to sell, modify
or delete products (represented by scopes). A certain user may interact
with one product in the context of a tenant (Determined by the Pushing
claim) with an specific role and with some different role from other
tenant.

- Resource:
  * product (With scopes sell and update)

- Roles:
  * Seller
  * Product-Manager

- Policies:
  * Is-Seller (In the Tenant specified in the Pushing Claim "tenant")
  * Is-Product-Manager (In the Tenant specified in the Pushing Claim
"tenant")

- Permissions:
  * product:sell -> Provides the "sell" scope of the resource "product" if
the "Is-Seller" policy evaluates to grant.
  * product:update -> Provides the "update" scope of the resource
"product" if the "Is-Product-Manager" policy evaluates to grant.

- Users:
  * Alice -> Alice is "Seller" in the tenant "Organization-1" and is
"Product-Manager" in the tenant "Organization 2" so she should be able to
sell products in the context of the tenant "Organization-1" and update
products in the context of "Organization-2" but neither "update" products
in the context of "Organization-1" or sell products in the context of
"Organization-2".

1.- Alice requests an RPT using the following ticket:
     { "resource": "product", "resource_scopes": ["sell"], "claims": {
"tenant": ["Organization-1"] } }

    Since Alice is "Seller" in the "Organization-1" (meaning the Policy
"Is-Seller" will evaluate to "grant" if the provided claim value is
"Organization-1" and the evaluated Identity is Alice) an RPT is emitted
with the following "permission" claim:

    [{
       "resource": "product",
       "resource_scopes": ["sell"],
       "claims": { "tenant": ["Organization-1"] }
    }]

2.- Alice upgrades the previous RPT with the following ticket:
     { "resource": "product", "resource_scopes": ["update"], "claims": {
"tenant": ["Organization-2"] } }

   Here is were things get confusing to us. We'd expect Alice to be granted
when requesting the scope "update" in the context of "Organization-2" since
Alice has the role "Product-Manager" in that tenant. That would be what
happened if Alice was requesting the RPT for the first time instead of
upgrading a previous one. However, since we are upgrading the RPT obtained
in Step 1, when the policy "Is-Product-Manager" is evaluated, the claim
"tenant" is mixed with the one in Step 1 (Since they are not grouped by
scope) resulting in the following permission:

   {
      "resource": "product",
      "resource_scopes": ["sell", "update"],
      "claims": {
          "tenant": ["Organization-1", "Organization-2"]
       }
   }

  The policy can't evaluate to grant since Alice is not "Product-Manager"
in both tenants "Organization-1" and "Organization-2" (Obtained through
$evaluation.getPermission().getClaims()). When evaluating this policy we
would only be interested in the pushing-claim `{ "tenant":
["Organization-2"] }` which was pushed along with the scope "update" (which
is the one being evaluated by the permission "product:update" associated
with this Policy).

   Shouldn't the claims be grouped by the scopes which with they were
pushed along? (See example at the end of this text), Are we missing
something?

   Example:
   {
      "resource": "product",
      "resource_scopes": [
          { "name": "sell", "claims": { "tenant": ["Organization-1"] } },
          { "name": "update", "claims": { "tenant": ["Organization-2"] } },
      ]

Thanks in advance,
Álvaro.