[keycloak-dev] fine-grain admin permissions with Authz

[Bill Burke]

I'm looking into how we could implement fine-grain admin permissions 
with Pedro's Authz service, i.e. fix our long standing bug that 
manage-users allows people to grant themselves admin roles.  I want to 
do an exercise of how certain things can be modeled, specific user role 
mappings.

Some things we want to be able to do

* admin can only assign specific roles to users

* admin can only assign specific roles to users of a specific group


The entire realm would be a Authz resource server.  There's already a 
client (resource server) for the realm "realm-management".

- A Scope of "user-role-mapping" would be defined.

These resources would be defined and would have the "user-role-mapping" 
scope attached to them.

* "Users" resource.  This resource represents all users in the system
* A resource is created per role
* A resource is created per group

Now, when managing roles for a user, we need to ask two questions:

1. Can the admin manage role mappings for this user?
2. Can the admin manage role mappings for this role?

For the first question, let's map the current behavior of Keycloak onto 
the Authz service.

* A scoped-base permission would be created for the "Users" resource 
with a scope of "user-role-mapping" and a role policy of role 
"manage-users".

When role mapping happens, the operation would make an entitlement 
request for "Users" with a scope of "user-role-mapping".  This would 
pass by default because of the default permission defined above. Now 
what about the case where we only want an admin to be able to manage 
roles for a specific group?  In this case we define a resource for the 
Group Foo.  The Group Foo would be attached to the "user-role-mapping" 
scope.  Then the realm admin would define a scope-based permission for 
the Group Foo resource and "user-role-mapping".  For example, there 
might be a "foo-admin" role.  The scope permission could grant the 
permission if the admin has the "foo-admin" role.

So, if the "Users"->"user-role-mapping" evaluation fails, the role 
mapping operation would then cycle through each Group of the user being 
managed and see if "Group Foo"->"user-role-mapping" evaluates correctly.

That's only half of a solution to our problem.  We also want to control 
what roles an admin is allowed to manage.  In this case we would have a 
resource defined for each role in the system.  A scoped-based permission 
would be created for the role's resource and the "user-role-mapping" 
scope.  For example, let's say we wanted to say that only admins with 
the "admin-role-mapper" role can assign admin roles like "manage-users" 
or "manage-realm".  For the "manage-realm" role resource, we would 
define a scoped-based permission for "user-role-mapping" with a role 
policy of "admin-role-mapper".

So, let's put this all together.  The role mapping operation would do 
these steps:

1. Can the admin manage role mappings for this user?
1.1 Evaluate that admin can access "user-role-mapping" scope for "Users" 
resource.  If success, goto 2.
1.2 For each group of the user being managed, evaluate that the admin 
can access "user-role-mapping" scope for that Group.  If success goto 2
1.3 Fail the role mapping operation
2. Is the admin allowed to assign the specific role?
2.1 Evaluate that the admin can access the "user-role-mapping" scope for 
the role's resource.