This PR introduces a way to implement Attribute Based Access Control
(ABAC) for the Llama Stack server.
The rough design is:
- https://github.com/meta-llama/llama-stack/pull/1626 added a way for
the Llama Stack server to query an authenticator
- We build upon that and expect "access attributes" as part of the
response. These attributes indicate the scopes available for the
request.
- We use these attributes to perform access control for registered
resources as well as for constructing the default access control
policies for newly created resources.
- By default, if you support authentication but don't return access
attributes, we will add a unique namespace pointing to the API_KEY. That
way, all resources by default will be scoped to API_KEYs.
An important aspect of this design is that Llama Stack stays out of the
business of credential management or the CRUD for attributes. How you
manage your namespaces or projects is entirely up to you. The design
only implements access control checks for the metadata / book-keeping
information that the Stack tracks.
### Limitations
- Currently, read vs. write vs. admin permissions aren't made explicit,
but this can be easily extended by adding appropriate attributes to the
`AccessAttributes` data structure.
- This design does not apply to agent instances since they are not
considered resources the Stack knows about. Agent instances are
completely within the scope of the Agents API provider.
### Test Plan
Added unit tests, existing integration tests
This PR adds support (or is a proposal for) for supporting API KEY
authentication on the Llama Stack server end. `llama-stack-client`
already supports accepting an api_key parameter and passes it down
through every request as an `Authentication: ` header.
Currently, Llama Stack does not propose APIs for handling authentication
or authorization for resources of any kind. Given that, and the fact
that any deployment will typically have _some_ authentication system
present, we simply adopt a delegation mechanism: delegate to an HTTPS
endpoint performing key management / authentication.
It is configured via:
```yaml
server:
auth:
endpoint: <...>
```
in the run.yaml configuration.
## How It Works
When authentication is enabled:
1. Every API request must include an `Authorization: Bearer <token>`
header
2. The server will send a _POST_ validation request to the configured
endpoint with the following payload:
```json
{
"api_key": "<token>",
"request": {
"path": "/api/path",
"headers": { "header1": "value1", ... },
"params": { "param1": "value1", ... }
}
}
```
3. If the authentication endpoint returns a 200 status code, the request
is allowed to proceed
4. If the authentication endpoint returns any other status code, a 401
Unauthorized response is returned
## Test Plan
Unit tests
