[Bugfix][Frontend] Require API key for top-level control-plane endpoints

[AUTHENSOR]

Purpose

AuthenticationMiddleware only authenticates request paths that start with the API prefixes (/v1, /v2, /inference, /cohere). However, several stateful control-plane endpoints are mounted at the top level, outside those prefixes, so on a server started with --api-key they were reachable without any credentials by anyone who could reach the port:

• POST /scale_elastic_ep, POST /is_scaling_elastic_ep: arms a global "scaling" flag that makes ScalingMiddleware return 503 to every request (including valid-key clients) for the duration of the operation, then calls engine_client.scale_elastic_ep() with caller-chosen new_data_parallel_size / drain_timeout (on Ray-DP elastic-EP deployments this adds/removes engine workers).
• POST /abort_requests (disaggregated tokens-only setup): aborts arbitrary request ids.
• POST /start_profile, POST /stop_profile: profiler control.
• POST /tokenize, POST /detokenize (prefix also covers /tokenizer_info): tokenizer access.

Proof of concept against an unmodified server started with --api-key:

[1] POST /v1/chat/completions no-auth   -> 401
[2] unauth POST /scale_elastic_ep accepted; scaling flag set = True
[3] POST /v1/chat/completions VALID key -> 503 {"error":"The model is currently scaling. ..."}
[4] scale op completed unauth           -> 200 {"message":"Scaled to 1 data parallel engines"}
[5] re-arm POST /scale_elastic_ep       -> 200 (repeatable)

Fix: extend the existing GUARDED_PREFIX tuple with these top-level paths — same middleware, same startswith idiom, no routes moved and no new dependency. Requests to those paths now return 401 exactly like /v1/* when a key is configured.

Behavior change: unauthenticated requests to those endpoints are now rejected when --api-key is set. Deployments that (deliberately) called /tokenize etc. without a key on a key-protected server must now send the key. Behavior is unchanged when no API key is configured (the middleware is not installed), and CORS preflights (OPTIONS) and /health remain open as before.

Deliberately not covered: the disaggregated /generate P/D protocol endpoint and sagemaker /invocations (inter-service protocol endpoints where auth is a separate design question), and VLLM_SERVER_DEV_MODE routers (local-development-only).

Test Plan

Added test_control_plane_routes_require_auth to tests/entrypoints/serve/middleware/test_authentication_middleware.py, covering all seven paths: missing token -> 401, wrong token -> 401, valid token -> 200. The module's existing route auto-discovery tests pick the new prefixes up automatically.

PYTHONPATH=. python3 -m pytest tests/entrypoints/serve/middleware/test_authentication_middleware.py -q

Test Result

• New test passes locally (1 passed). The parametrized auto-discovery tests could not complete on this macOS host (local env lacks transformers v5; pre-existing MPS allocator teardown crash) — relying on CI for the parametrized sweep.
• End-to-end PoC against a stubbed engine before the fix: unauthenticated POST /scale_elastic_ep was accepted, the scaling flag was set, and subsequent valid-key requests got 503. After the fix: unauthenticated POST /scale_elastic_ep -> 401 {"error":"Unauthorized"} (same for /is_scaling_elastic_ep, /start_profile, /abort_requests, /tokenize), while an authenticated call still scales normally ("Scaled to 2 data parallel engines").

[claude]

Claude Code Review

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Team

Run ID: ce039774-5891-4d90-93ce-9bc1c3b78856

📥 Commits

Reviewing files that changed from the base of the PR and between f2e2936 and 9d9e6e3.

📒 Files selected for processing (2)

• tests/entrypoints/serve/middleware/test_authentication_middleware.py
• vllm/entrypoints/serve/middleware/authenticate.py

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Summary

Summary by CodeRabbit

• Security
  • API-key authentication is now required for additional engine management, profiling, scaling, tokenization, detokenization, and request-abort endpoints.
  • Requests without valid credentials to these endpoints are rejected with an unauthorized response.

Walkthrough

The authentication middleware now guards seven additional control-plane, tokenizer, and detokenizer endpoints. Tests verify that these routes reject missing or invalid tokens and accept valid tokens.

Changes

Authentication coverage

Layer / File(s)	Summary
Expand guarded route prefixes vllm/entrypoints/serve/middleware/authenticate.py	GUARDED_PREFIX now includes seven control-plane, tokenizer, and detokenizer endpoints.
Validate control-plane authentication tests/entrypoints/serve/middleware/test_authentication_middleware.py	The test defines the new paths and checks 401 responses for missing or invalid tokens and a 200 response for a valid token.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 9d9e6

This change requires API-key authentication for additional control-plane and tokenizer endpoints when authentication is enabled, while tests cover rejected unauthenticated requests and accepted valid-key requests. No current merge-blocking risk is identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: requiring API-key authentication for top-level control-plane endpoints.
Description check	✅ Passed	The description directly explains the authentication issue, affected endpoints, behavior change, tests, and scope.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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[DarkLight1337]

This behavior is intentional. See https://docs.vllm.ai/en/latest/usage/security/?h=sec#api-key-authentication-limitations