Feat: Rate-limit login endpoint to block brute-force attacks

After LOGIN_MAX_FAILURES consecutive failed attempts from the same source
IP within LOGIN_WINDOW_SECONDS, POST /api/v1/auth/token returns HTTP 429
with a Retry-After header for LOGIN_COOLDOWN_SECONDS. A successful login
resets the counter. Trusted upstream proxy IPs/CIDRs can be declared via
LOGIN_TRUSTED_PROXY_IPS so X-Forwarded-For is honoured correctly behind
nginx ingress or similar reverse proxies.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/app/routers/auth.py

@@ -1,7 +1,9 @@
-from fastapi import APIRouter, Depends, HTTPException
+from fastapi import APIRouter, Depends, HTTPException, Request
+from fastapi.responses import JSONResponse
 from pydantic import BaseModel
 
 from app.auth.jwt_provider import JWTAuthProvider
+from app.auth.rate_limiter import LoginRateLimiter, get_client_ip
 from app.dependencies import get_jwt_auth
 
 router = APIRouter(tags=["auth"])
@@ -19,12 +21,32 @@ class TokenResponse(BaseModel):
 
 
 @router.post("/auth/token", response_model=TokenResponse)
-async def login(body: LoginRequest, auth: JWTAuthProvider = Depends(get_jwt_auth)):
+async def login(
+    request: Request,
+    body: LoginRequest,
+    auth: JWTAuthProvider = Depends(get_jwt_auth),
+):
+    limiter: LoginRateLimiter = request.app.state.login_rate_limiter
+    ip: str = get_client_ip(request, request.app.state.login_trusted_networks)
+
+    if limiter.is_blocked(ip):
+        return JSONResponse(
+            status_code=429,
+            content={
+                "detail": "Too many failed login attempts. Please try again later.",
+                "code": "login_rate_limited",
+            },
+            headers={"Retry-After": str(limiter.cooldown_seconds)},
+        )
+
     if not auth.verify_credentials(body.username, body.password):
+        limiter.record_failure(ip)
         raise HTTPException(
             status_code=401,
             detail={"detail": "Invalid credentials", "code": "invalid_credentials"},
         )
+
+    limiter.record_success(ip)
     token = auth.create_token()
     return TokenResponse(
         access_token=token,