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>

llama_stack/providers/inline/agents/meta_reference/persistence.py

@@ -10,9 +10,10 @@ import uuid
 from datetime import datetime, timezone
 
 from llama_stack.apis.agents import AgentConfig, Session, ToolExecutionStep, Turn
-from llama_stack.distribution.access_control import check_access
-from llama_stack.distribution.datatypes import AccessAttributes
-from llama_stack.distribution.request_headers import get_auth_attributes
+from llama_stack.distribution.access_control.access_control import AccessDeniedError, is_action_allowed
+from llama_stack.distribution.access_control.datatypes import AccessRule
+from llama_stack.distribution.datatypes import User
+from llama_stack.distribution.request_headers import get_authenticated_user
 from llama_stack.providers.utils.kvstore import KVStore
 
 log = logging.getLogger(__name__)
@@ -22,7 +23,9 @@ class AgentSessionInfo(Session):
     # TODO: is this used anywhere?
     vector_db_id: str | None = None
     started_at: datetime
-    access_attributes: AccessAttributes | None = None
+    owner: User | None = None
+    identifier: str | None = None
+    type: str = "session"
 
 
 class AgentInfo(AgentConfig):
@@ -30,24 +33,27 @@ class AgentInfo(AgentConfig):
 
 
 class AgentPersistence:
-    def __init__(self, agent_id: str, kvstore: KVStore):
+    def __init__(self, agent_id: str, kvstore: KVStore, policy: list[AccessRule]):
         self.agent_id = agent_id
         self.kvstore = kvstore
+        self.policy = policy
 
     async def create_session(self, name: str) -> str:
         session_id = str(uuid.uuid4())
 
         # Get current user's auth attributes for new sessions
-        auth_attributes = get_auth_attributes()
-        access_attributes = AccessAttributes(**auth_attributes) if auth_attributes else None
+        user = get_authenticated_user()
 
         session_info = AgentSessionInfo(
             session_id=session_id,
             session_name=name,
             started_at=datetime.now(timezone.utc),
-            access_attributes=access_attributes,
+            owner=user,
             turns=[],
+            identifier=name,  # should this be qualified in any way?
         )
+        if not is_action_allowed(self.policy, "create", session_info, user):
+            raise AccessDeniedError()
 
         await self.kvstore.set(
             key=f"session:{self.agent_id}:{session_id}",
@@ -73,10 +79,10 @@ class AgentPersistence:
     def _check_session_access(self, session_info: AgentSessionInfo) -> bool:
         """Check if current user has access to the session."""
         # Handle backward compatibility for old sessions without access control
-        if not hasattr(session_info, "access_attributes"):
+        if not hasattr(session_info, "access_attributes") and not hasattr(session_info, "owner"):
             return True
 
-        return check_access(session_info.session_id, session_info.access_attributes, get_auth_attributes())
+        return is_action_allowed(self.policy, "read", session_info, get_authenticated_user())
 
     async def get_session_if_accessible(self, session_id: str) -> AgentSessionInfo | None:
         """Get session info if the user has access to it. For internal use by sub-session methods."""