feat(auth): allow token to be provided for use against jwks endpoint (#2394)

Though the jwks endpoint does not usually require authentication, it
does in a kubernetes cluster. While the cluster can be configured to
allow anonymous access to that endpoint, this avoids the need to do so.

tests/unit/server/test_auth.py

@@ -345,6 +345,56 @@ def test_invalid_oauth2_authentication(oauth2_client, invalid_token):
     assert "Invalid JWT token" in response.json()["error"]["message"]
 
 
+async def mock_auth_jwks_response(*args, **kwargs):
+    if "headers" not in kwargs or "Authorization" not in kwargs["headers"]:
+        return MockResponse(401, {})
+    authz = kwargs["headers"]["Authorization"]
+    if authz != "Bearer my-jwks-token":
+        return MockResponse(401, {})
+    return await mock_jwks_response(args, kwargs)
+
+
+@pytest.fixture
+def oauth2_app_with_jwks_token():
+    app = FastAPI()
+    auth_config = AuthenticationConfig(
+        provider_type=AuthProviderType.OAUTH2_TOKEN,
+        config={
+            "jwks": {
+                "uri": "http://mock-authz-service/token/introspect",
+                "key_recheck_period": "3600",
+                "token": "my-jwks-token",
+            },
+            "audience": "llama-stack",
+        },
+    )
+    app.add_middleware(AuthenticationMiddleware, auth_config=auth_config)
+
+    @app.get("/test")
+    def test_endpoint():
+        return {"message": "Authentication successful"}
+
+    return app
+
+
+@pytest.fixture
+def oauth2_client_with_jwks_token(oauth2_app_with_jwks_token):
+    return TestClient(oauth2_app_with_jwks_token)
+
+
+@patch("httpx.AsyncClient.get", new=mock_auth_jwks_response)
+def test_oauth2_with_jwks_token_expected(oauth2_client, jwt_token_valid):
+    response = oauth2_client.get("/test", headers={"Authorization": f"Bearer {jwt_token_valid}"})
+    assert response.status_code == 401
+
+
+@patch("httpx.AsyncClient.get", new=mock_auth_jwks_response)
+def test_oauth2_with_jwks_token_configured(oauth2_client_with_jwks_token, jwt_token_valid):
+    response = oauth2_client_with_jwks_token.get("/test", headers={"Authorization": f"Bearer {jwt_token_valid}"})
+    assert response.status_code == 200
+    assert response.json() == {"message": "Authentication successful"}
+
+
 def test_get_attributes_from_claims():
     claims = {
         "sub": "my-user",