# Auth-gate Security Model

## Authentication flow

1. Client request arrives at NGINX.
2. NGINX sends an internal auth_request subrequest to auth-gate.
3. Auth-gate checks:
   - Is the IP in the permanent whitelist? → Allow.
   - Is the IP in the temporary whitelist and not expired? → Allow.
   - Does the Authorization header contain valid Basic Auth? → Allow.
   - Otherwise → 401 Unauthorized.
4. NGINX passes the request to the upstream service if auth-gate returned 200.
5. NGINX returns 401 to the client if auth-gate returned 401/403.

## IP handling

### Permanent whitelist

- Loaded from a file mounted as a volume.
- The file is polled every 30 seconds (configurable).
- Only single IPs and CIDR ranges (as strings) are supported.
- The file is reloaded only when its mtime changes.

### Temporary whitelist

- In-memory store.
- Entries expire after their TTL.
- The cleanup goroutine runs every 60 seconds (configurable) to remove expired entries.
- No persistence across restarts.

## API key

The API key is the only secret for the /api/* endpoints. It's sent as a bearer token
in the Authorization header.

- Keep it secret. Don't log it. Don't put it in the URL.
- Use a strong random string.
- Rotate it regularly.

## Basic Auth

The Basic Auth credentials are set via environment variables. The username is `admin`
by default, and the password is `changeme` by default.

- Change both immediately on first use.
- Use strong passwords.
- The credentials are sent in the Authorization header (base64-encoded).
- Always serve the auth endpoint over TLS.

## File watcher

The permanent whitelist file watcher polls the file every 30 seconds. It only
reloads if the file's mtime has changed. This means:

- Frequent touch-operations don't cause unnecessary reloads.
- The watcher is simple and doesn't depend on inotify.

## Graceful shutdown

The service listens for SIGTERM and SIGINT. On signal:

1. Stop accepting new connections.
2. Close idle connections.
3. Wait for in-flight requests to complete (up to 30 seconds).
4. Exit.

This ensures Docker deployments can shut down cleanly.

## What we don't do

- We don't support JWT/OAuth. If you need these, add them later.
- We don't support session state. The auth decision is made per-request.
- We don't support rate limiting. Use NGINX's limit_req for that.
- We don't support IP-based rate limiting. Use NGINX's limit_conn for that.
- We don't support IPv6. If you need IPv6, add it later.
- We don't support TLS. The auth endpoint should always be served over TLS.
- We don't support logging to a file. Logs go to stdout (Docker).
- We don't support metrics. If you need metrics, add them later.
- We don't support health checks with Prometheus. The /status endpoint is a simple text response.
- We don't support configuration via a config file. Use environment variables.
- We don't support multiple domains. The auth-gate service doesn't care about domains.
- We don't support HTTP/2. The auth-gate service uses HTTP/1.1 only.
- We don't support WebSocket. The auth-gate service doesn't need WebSocket.
- We don't support gRPC. The auth-gate service is a simple REST API.