Issue #8: add grpc authentication and scope authorization

docs/gateway-process-design.md

@@ -612,6 +612,15 @@ hashes the presented secret, and compares the stored and presented hashes with
 results distinguish malformed credentials, missing keys, revoked keys, missing
 pepper configuration, and hash mismatch for internal authorization handling.
 
+`GatewayGrpcAuthorizationInterceptor` enforces this authentication model for
+public gRPC calls. Missing, malformed, revoked, unknown, or mismatched keys fail
+with `Unauthenticated`. Authenticated calls missing the scope required by the
+RPC fail with `PermissionDenied`. The interceptor applies to unary calls and
+server-streaming calls and stores the authenticated `ApiKeyIdentity` in
+`IGatewayRequestIdentityAccessor` for the duration of the request handler.
+`Authentication:Mode` set to `Disabled` bypasses API-key verification for local
+development only.
+
 Recommended scopes:
 
 - `session:open`
@@ -677,6 +686,20 @@ Commands requiring authorization:
 - worker shutdown diagnostics,
 - metadata queries if they expose sensitive plant structure.
 
+Current gRPC scope mapping:
+
+- `OpenSession` requires `session:open`.
+- `CloseSession` requires `session:close`.
+- `StreamEvents` and `DrainEvents` require `events:read`.
+- read-style MXAccess commands such as `Register`, `AddItem`, `Advise`, and
+  `Ping` require `invoke:read`.
+- `Write` and `Write2` require `invoke:write`.
+- `WriteSecured`, `WriteSecured2`, and `AuthenticateUser` require
+  `invoke:secure`.
+- metadata commands such as `ArchestrAUserToId`, `GetSessionState`, and
+  `GetWorkerInfo` require `metadata:read`.
+- `ShutdownWorker` requires `admin`.
+
 ### Worker IPC
 
 Named pipes should be local only. Pipe ACLs should restrict access to:
@@ -819,6 +842,9 @@ workers and fake transports.
 Focused tests:
 
 - session state transitions,
+- gRPC API-key authentication for unary and streaming calls,
+- gRPC scope mapping for sessions, invokes, events, metadata, and admin
+  commands,
 - worker startup failures,
 - protocol version mismatch,
 - malformed frame handling,