feat: fine grained access control policy (#2264)

This allows a set of rules to be defined for determining access to
resources. The rules are (loosely) based on the cedar policy format.

A rule defines a list of action either to permit or to forbid. It may
specify a principal or a resource that must match for the rule to take
effect. It may also specify a condition, either a 'when' or an 'unless',
with additional constraints as to where the rule applies.

A list of rules is held for each type to be protected and tried in order
to find a match. If a match is found, the request is permitted or
forbidden depening on the type of rule. If no match is found, the
request is denied. If no rules are specified for a given type, a rule
that allows any action as long as the resource attributes match the user
attributes is added (i.e. the previous behaviour is the default.

Some examples in yaml:

```
    model:
    - permit:
      principal: user-1
      actions: [create, read, delete]
      comment: user-1 has full access to all models
    - permit:
      principal: user-2
      actions: [read]
      resource: model-1
      comment: user-2 has read access to model-1 only
    - permit:
      actions: [read]
      when:
        user_in: resource.namespaces
      comment: any user has read access to models with matching attributes
    vector_db:
    - forbid:
      actions: [create, read, delete]
      unless:
        user_in: role::admin
      comment: only user with admin role can use vector_db resources
```

---------

Signed-off-by: Gordon Sim <gsim@redhat.com>

tests/unit/server/test_auth.py

@@ -139,7 +139,7 @@ async def mock_post_success(*args, **kwargs):
         {
             "message": "Authentication successful",
             "principal": "test-principal",
-            "access_attributes": {
+            "attributes": {
                 "roles": ["admin", "user"],
                 "teams": ["ml-team", "nlp-team"],
                 "projects": ["llama-3", "project-x"],
@@ -233,7 +233,7 @@ async def test_http_middleware_with_access_attributes(mock_http_middleware, mock
             {
                 "message": "Authentication successful",
                 "principal": "test-principal",
-                "access_attributes": {
+                "attributes": {
                     "roles": ["admin", "user"],
                     "teams": ["ml-team", "nlp-team"],
                     "projects": ["llama-3", "project-x"],
@@ -255,33 +255,6 @@ async def test_http_middleware_with_access_attributes(mock_http_middleware, mock
         mock_app.assert_called_once_with(mock_scope, mock_receive, mock_send)
 
 
-@pytest.mark.asyncio
-async def test_http_middleware_no_attributes(mock_http_middleware, mock_scope):
-    """Test middleware behavior with no access attributes"""
-    middleware, mock_app = mock_http_middleware
-    mock_receive = AsyncMock()
-    mock_send = AsyncMock()
-
-    with patch("httpx.AsyncClient") as mock_client:
-        mock_client_instance = AsyncMock()
-        mock_client.return_value.__aenter__.return_value = mock_client_instance
-
-        mock_client_instance.post.return_value = MockResponse(
-            200,
-            {
-                "message": "Authentication successful"
-                # No access_attributes
-            },
-        )
-
-        await middleware(mock_scope, mock_receive, mock_send)
-
-        assert "user_attributes" in mock_scope
-        attributes = mock_scope["user_attributes"]
-        assert "roles" in attributes
-        assert attributes["roles"] == ["test.jwt.token"]
-
-
 # oauth2 token provider tests
 
 
@@ -380,16 +353,16 @@ def test_get_attributes_from_claims():
         "aud": "llama-stack",
     }
     attributes = get_attributes_from_claims(claims, {"sub": "roles", "groups": "teams"})
-    assert attributes.roles == ["my-user"]
-    assert attributes.teams == ["group1", "group2"]
+    assert attributes["roles"] == ["my-user"]
+    assert attributes["teams"] == ["group1", "group2"]
 
     claims = {
         "sub": "my-user",
         "tenant": "my-tenant",
     }
     attributes = get_attributes_from_claims(claims, {"sub": "roles", "tenant": "namespaces"})
-    assert attributes.roles == ["my-user"]
-    assert attributes.namespaces == ["my-tenant"]
+    assert attributes["roles"] == ["my-user"]
+    assert attributes["namespaces"] == ["my-tenant"]
 
     claims = {
         "sub": "my-user",
@@ -408,9 +381,9 @@ def test_get_attributes_from_claims():
             "groups": "teams",
         },
     )
-    assert set(attributes.roles) == {"my-user", "my-username"}
-    assert set(attributes.teams) == {"my-team", "group1", "group2"}
-    assert attributes.namespaces == ["my-tenant"]
+    assert set(attributes["roles"]) == {"my-user", "my-username"}
+    assert set(attributes["teams"]) == {"my-team", "group1", "group2"}
+    assert attributes["namespaces"] == ["my-tenant"]
 
 
 # TODO: add more tests for oauth2 token provider