Add Cloudflare Turnstile verification middleware

.github/workflows/test.yaml

@@ -37,6 +37,6 @@ jobs:
 
       - name: Smoke test /health endpoint
         run: |
-          docker run -d --name smoke -e PORT=8080 -e OPENAI_API_KEY=test -p 8080:8080 signwriting-description
+          docker run -d --name smoke -e PORT=8080 -e OPENAI_API_KEY=test -e TURNSTILE_SECRET_KEY=1x0000000000000000000000000000000AA -p 8080:8080 signwriting-description
           sleep 5 # wait for uvicorn cold start
           curl -sf http://localhost:8080/health

signwriting_description/server.py

@@ -1,9 +1,10 @@
 import os
 from datetime import UTC, datetime
 
+import httpx
 import uvicorn
 from dotenv import load_dotenv
-from fastapi import FastAPI, HTTPException, Query
+from fastapi import FastAPI, HTTPException, Query, Request
 from fastapi.responses import JSONResponse
 from signwriting.formats.fsw_to_sign import fsw_to_sign
 
@@ -15,9 +16,35 @@
 if not OPENAI_API_KEY:
     raise RuntimeError("Missing OPENAI_API_KEY environment variable")
 
+TURNSTILE_SECRET_KEY = os.getenv("TURNSTILE_SECRET_KEY")
+if not TURNSTILE_SECRET_KEY:
+    raise RuntimeError("Missing TURNSTILE_SECRET_KEY environment variable")
+
 app = FastAPI(title="Signwriting Description API")
 
 
+
+@app.middleware("http")
+async def turnstile_verification(request: Request, call_next):
+    if request.url.path == "/health":
+        return await call_next(request)
+
+    token = request.headers.get("cf-turnstile-response")
+    if not token:
+        return JSONResponse(status_code=403, content={"error": "Missing Turnstile token"})
+
+    async with httpx.AsyncClient() as client:
+        result = await client.post(
+            "https://challenges.cloudflare.com/turnstile/v0/siteverify",
+            data={"secret": TURNSTILE_SECRET_KEY, "response": token},
+        )
+
+    if not result.json().get("success"):
+        return JSONResponse(status_code=403, content={"error": "Invalid Turnstile token"})
+
+    return await call_next(request)
+
+
 @app.get("/health")
 def health():
     return {