# Flask

> Monitor a Flask app: an after-request hook logging status, sign-in lines from your login view, and beam monitor with the Flask rules, including the Werkzeug debugger console.

Source: https://docs.agentbeam.com/cookbooks/frameworks/flask

## How Beam reads a Flask app

There's no in-process SDK for this stack, so the app writes what Beam needs to its logs and [`beam monitor`](https://docs.agentbeam.com/agent-cli/app-monitoring#install-and-start) reads them on the same server or container. Only redacted findings leave it. Two kinds of line:

- **One JSON line per request**, with `method`, `path` (with the query string), `status`, `ip`, `user_agent`, `host` and `duration_ms`. The status is what lets Beam tell an attack your app refused from one it answered.
- **Security events as plain lines**, worded like this (Beam matches the wording and reads `user=` and `ip=`):

```text
login failed user=42 ip=203.0.113.7
login succeeded user=42 ip=203.0.113.7
granted admin role to user=99 by user=12
API key created user=12
{"event":"llm_usage","user":"42","model":"gpt-5","total_tokens":1834}
```

Use an opaque user id, never an email. New outbound hosts are only reported by the Node.js SDK; for this stack, restrict outbound traffic at the network instead.

## Before you start

Do steps 1 and 2 of the [general cookbook](https://docs.agentbeam.com/cookbooks/app-monitoring#step-1-turn-it-on-and-create-the-apps-token) first: App monitoring is on, the app is added, and its `beam_app_` token is in your secret store as `BEAM_APP_TOKEN`. Everything below needs `@agent-beam/beam` 0.2.32 or newer.

## Log each request with its status

```python
# beam_logging.py
import json, logging, time
from flask import g, request

requests_log = logging.getLogger("beam.requests")
security = logging.getLogger("beam.security")

def client_ip():
    forwarded = request.headers.get("X-Forwarded-For")
    return forwarded.split(",")[0].strip() if forwarded else request.remote_addr

def init_beam(app):
    for name, path in (("beam.requests", "/var/log/app/requests.log"), ("beam.security", "/var/log/app/security.log")):
        handler = logging.handlers.WatchedFileHandler(path)
        handler.setFormatter(logging.Formatter("%(message)s"))
        logger = logging.getLogger(name)
        logger.addHandler(handler)
        logger.setLevel(logging.INFO)
        logger.propagate = False

    @app.before_request
    def start_timer():
        g.beam_started = time.monotonic()

    @app.after_request
    def log_request(response):
        requests_log.info(json.dumps({
            "method": request.method,
            "path": request.full_path.rstrip("?"),
            "status": response.status_code,
            "ip": client_ip(),
            "user_agent": request.headers.get("User-Agent", ""),
            "host": request.host,
            "duration_ms": round((time.monotonic() - g.get("beam_started", time.monotonic())) * 1000),
        }))
        return response
```

Add `import logging.handlers` at the top, and call `init_beam(app)` where you create the app.

## Log sign-ins, admins and keys

```python
from beam_logging import security, client_ip

@app.post("/login")
def login():
    user = verify_password(request.form["username"], request.form["password"])
    if not user:
        security.warning("login failed user=%s ip=%s", user_id_for(request.form["username"]), client_ip())
        return {"error": "Invalid credentials"}, 401
    security.info("login succeeded user=%s ip=%s", user.id, client_ip())
    login_user(user)
    return redirect("/")
```

Log `granted admin role to user=... by user=...`, `API key created user=...` and an `llm_usage` JSON line in the same way where those happen.

## Run `beam monitor` next to the app

```sh
npm install -g @agent-beam/beam
beam monitor --stack flask --file /var/log/app/requests.log --file /var/log/app/security.log --app /srv/app
```

`--stack flask` turns on this framework's rules and rolls up attacks on frameworks you don't run; `--app` also checks the app's lockfiles daily (and would detect the stack on its own). Keep it running with systemd:

```ini
# /etc/systemd/system/beam-monitor.service
[Unit]
Description=AgentBeam App monitoring
After=network-online.target

[Service]
EnvironmentFile=/etc/beam/app.env
ExecStart=/usr/bin/env beam monitor --stack flask --file /var/log/app/requests.log --file /var/log/app/security.log --app /srv/app
Restart=always
User=beam

[Install]
WantedBy=multi-user.target
```

```sh
sudo install -m 600 /dev/null /etc/beam/app.env && echo "BEAM_APP_TOKEN=beam_app_..." | sudo tee /etc/beam/app.env >/dev/null
sudo systemctl daemon-reload && sudo systemctl enable --now beam-monitor
```

In Docker or Kubernetes, run the same command in a sidecar that mounts the log directory read-only, with `BEAM_APP_TOKEN` from a secret.
## Prove it works

```sh
beam monitor status   # app, level, stack, usage
beam monitor test     # a test finding through your alert workflows
curl -s "https://your-app.example.com/?id=1%20UNION%20SELECT%201" -o /dev/null
```

Within a minute, the SQL injection test shows on **App monitoring**: under **Needs action** if the app answered 2xx, or counted under "needed nothing from you" if it refused it. Then sign in to a test account with a wrong password ten times and the right one once: **Sign-in succeeded after 10 failed attempts** appears as critical.
## Check dependencies on every pull request

```yaml
# .github/workflows/beam-cve.yml
name: Dependency check
on: [pull_request]
jobs:
  cve:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npx -y @agent-beam/beam cve check . --fail-on high
        env:
          BEAM_APP_TOKEN: ${{ secrets.BEAM_APP_TOKEN }}
```

Pin your Python dependencies so they can be checked.
## What Beam watches for on this stack

Besides every [built-in rule](https://docs.agentbeam.com/agent-cli/app-monitoring#levels-and-detection) and the [attack-in-progress signals](https://docs.agentbeam.com/agent-cli/app-monitoring#signs-an-attack-is-underway):

| Rule | Means | Severity |
| --- | --- | --- |
| Werkzeug debugger console attempt | A request using `__debugger__=yes&cmd=`: code execution if the console is reachable | Critical |
| Werkzeug debugger console served | `/console` answered 2xx | Critical |

Attacks on other frameworks (WordPress probes, Laravel or Spring exploits, and so on) are rolled up as **Not your stack** when there's no status to say otherwise, and never alert.
## Close what Beam would catch

Beam raises these when they're found; better that there's nothing to find:

- Never run `app.run(debug=True)` or `FLASK_DEBUG=1` in production; serve with gunicorn or uWSGI.
- Set a strong `SECRET_KEY` from your secret store, and `SESSION_COOKIE_SECURE = True`.
- Use `ProxyFix` with the exact number of proxies so `request.remote_addr` can't be spoofed.
## Coverage checklist

| Feature | Done when |
| --- | --- |
| Request log with status | Findings show **Answered**, **Refused** or **Errored** |
| Stack declared | `beam monitor` prints the stack at start |
| Sign-in events | `login failed` and `login succeeded` lines are written |
| Admin and key events | Role grants and new keys are logged |
| LLM spend | An `llm_usage` line follows each model call |
| Dependency checks | The CI job runs on pull requests |
| Alerts | Critical pages someone, high reaches a channel ([step 8](https://docs.agentbeam.com/cookbooks/app-monitoring#step-8-send-alerts-to-the-right-place)) |
| Routine | Someone reads **Needs action** daily and **Attack analytics** weekly |