feat(gateway): add auth rate-limiting & brute-force protection (#15035)

* feat(gateway): add auth rate-limiting & brute-force protection

Add a per-IP sliding-window rate limiter to Gateway authentication
endpoints (HTTP, WebSocket upgrade, and WS message-level auth).

When gateway.auth.rateLimit is configured, failed auth attempts are
tracked per client IP. Once the threshold is exceeded within the
sliding window, further attempts are blocked with HTTP 429 + Retry-After
until the lockout period expires. Loopback addresses are exempt by
default so local CLI sessions are never locked out.

The limiter is only created when explicitly configured (undefined
otherwise), keeping the feature fully opt-in and backward-compatible.

* fix(gateway): isolate auth rate-limit scopes and normalize 429 responses

---------

Co-authored-by: buerbaumer <buerbaumer@users.noreply.github.com>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/gateway/server.impl.ts

@@ -43,6 +43,7 @@ import { startDiagnosticHeartbeat, stopDiagnosticHeartbeat } from "../logging/di
 import { createSubsystemLogger, runtimeForLogger } from "../logging/subsystem.js";
 import { getGlobalHookRunner } from "../plugins/hook-runner-global.js";
 import { runOnboardingWizard } from "../wizard/onboarding.js";
+import { createAuthRateLimiter, type AuthRateLimiter } from "./auth-rate-limit.js";
 import { startGatewayConfigReloader } from "./config-reload.js";
 import { ExecApprovalManager } from "./exec-approval-manager.js";
 import { NodeRegistry } from "./node-registry.js";
@@ -270,6 +271,12 @@ export async function startGatewayServer(
   let hooksConfig = runtimeConfig.hooksConfig;
   const canvasHostEnabled = runtimeConfig.canvasHostEnabled;
 
+  // Create auth rate limiter only when explicitly configured.
+  const rateLimitConfig = cfgAtStart.gateway?.auth?.rateLimit;
+  const authRateLimiter: AuthRateLimiter | undefined = rateLimitConfig
+    ? createAuthRateLimiter(rateLimitConfig)
+    : undefined;
+
   let controlUiRootState: ControlUiRootState | undefined;
   if (controlUiRootOverride) {
     const resolvedOverride = resolveControlUiRootOverrideSync(controlUiRootOverride);
@@ -340,6 +347,7 @@ export async function startGatewayServer(
     openResponsesEnabled,
     openResponsesConfig,
     resolvedAuth,
+    rateLimiter: authRateLimiter,
     gatewayTls,
     hooksConfig: () => hooksConfig,
     pluginRegistry,
@@ -478,6 +486,7 @@ export async function startGatewayServer(
     canvasHostEnabled: Boolean(canvasHost),
     canvasHostServerPort,
     resolvedAuth,
+    rateLimiter: authRateLimiter,
     gatewayMethods,
     events: GATEWAY_EVENTS,
     logGateway: log,
@@ -657,6 +666,7 @@ export async function startGatewayServer(
         skillsRefreshTimer = null;
       }
       skillsChangeUnsub();
+      authRateLimiter?.dispose();
       await close(opts);
     },
   };