appfirewall-fastapi

Origin-side abuse signal middleware for FastAPI apps behind Cloudflare.

Part of the AppFirewall platform by Sireto. Cloudflare protects your edge; AppFirewall sees what your CDN can't — parse failures, auth failures, and application-layer abuse signals at your origin — and closes the loop back to the edge.

Status: v0.1, pre-release. The public API (AppFirewallMiddleware, appfirewall.record) is stable; internals may change.

Install

pip install appfirewall-fastapi

Quick start

from fastapi import FastAPI
from appfirewall_fastapi import AppFirewallMiddleware

app = FastAPI()
app.add_middleware(
    AppFirewallMiddleware,
    api_key="afw_live_...",   # or set APPFIREWALL_API_KEY
)

That's it. The middleware will:

• Resolve the real client IP from cf-connecting-ip (validated against Cloudflare's published IP ranges — never spoofable from outside).
• Classify 404s as scanner / benign-miss / unknown using a pattern library of known probes (/wp-admin, /.env, /.git/config, path-traversal, etc.).
• Ship events in batches (2s / 500 events, gzipped JSONL) to the AppFirewall ingest endpoint out-of-band, so your request path is never blocked.

Recording app-layer signals

The value AppFirewall provides over edge-only protection comes from signals your app can see but Cloudflare can't. Use appfirewall.record() inside your handlers:

from fastapi import HTTPException, UploadFile
from appfirewall_fastapi import appfirewall

@app.post("/upload")
async def upload(file: UploadFile):
    try:
        parsed = parse_flint(await file.read())
    except ParseError as e:
        appfirewall.record("upload.parse_failed", reason=str(e))
        raise HTTPException(400, "invalid format")
    appfirewall.record("upload.success", size=len(parsed))
    return {"ok": True}

record() is synchronous, non-blocking, and never raises — safe to sprinkle anywhere. Outside a request, it's a silent no-op.

Configuration

All options can be passed as keyword arguments to add_middleware or set via environment variables.

Fail-open guarantees

This middleware is deliberately conservative:

• If the middleware crashes, your app still serves the request.
• If ingest is down, events are buffered and dropped silently when the buffer fills. A circuit breaker prevents retry storms.
• If the API key is missing, mode flips to "off" with a single warning.
• appfirewall.record() never raises, never blocks, never awaits.
• Request latency overhead target: <1ms p99.

The tradeoff: the SDK's default is observation, not enforcement. Blocking bad actors happens at the Cloudflare edge via the AppFirewall control plane, which this SDK feeds. This is the design. For local enforcement in emergencies, set enforce_rate_limit=True.

Local development

Point mode="local" at a file on disk to iterate without an ingest endpoint:

app.add_middleware(
    AppFirewallMiddleware,
    api_key="dev",
    mode="local",
    local_log_path="/tmp/appfirewall.jsonl",
)

Tail the file to watch events as your app runs:

tail -f /tmp/appfirewall.jsonl | jq .

Development

This SDK lives in the appfirewall-sdk monorepo under python/appfirewall-fastapi/. From this directory:

pip install -e ".[dev]"
pytest
mypy src/
ruff check src/

All three must pass. See ../../docs/CONTRIBUTING.md for the cross-SDK PR workflow and docs/ARCHITECTURE.md for this SDK's module layout and design decisions. If you're an AI coding agent, start with ../../AGENTS.md.

License

Apache-2.0.