Initial version of fail2ban-webui

Web interface to view, ban and unban fail2ban IPs on several hosts via
SSH, generalised from the private f2b-web tool.

- Web UI (Flask/Waitress): hosts.yaml, local/OIDC/proxy authentication,
  English/German UI, origin map, optional Loki/Grafana/GeoIP, CLI helpers
- Agent f2b-webctl with install.sh/uninstall.sh (dedicated user + sudo,
  from= restriction, protected networks, manual jail)
- Hardened Docker image, examples, documentation, smoke test, testbed

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/authentication.md

@@ -0,0 +1,119 @@
+# Authentication
+
+`AUTH_MODE` selects how users sign in. The container refuses to start without a working
+configuration – there is no unauthenticated mode.
+
+| Mode | Use when |
+|---|---|
+| `local` | one shared admin account is enough |
+| `oidc` | you have an identity provider (Authentik, Keycloak, Authelia, Zitadel, …) |
+| `local,oidc` | SSO with a local fallback account |
+| `proxy` | your reverse proxy already authenticates (forward auth, basic auth, IP allow list) |
+
+Every change (ban/unban) additionally needs the per-session CSRF token and a matching
+`Origin` header, and every action is written to the audit log with the user name.
+
+## Local user
+
+```bash
+docker compose run --rm -it fail2ban-webui hash-password
+```
+
+```ini
+AUTH_MODE=local
+AUTH_USER=admin
+AUTH_PASSWORD_HASH='scrypt:32768:8:1$…'
+```
+
+- Passwords need at least 12 characters; the hash is scrypt (Werkzeug).
+- After `LOGIN_MAX_ATTEMPTS` (5) failures a client IP is locked for `LOGIN_LOCK_MINUTES` (15).
+- Failed logins are logged as `LOGIN_FAILED user=… ip=…` – see
+  [operations.md](operations.md#protecting-the-login-with-fail2ban) to let fail2ban ban
+  them at the proxy.
+- Set `TRUSTED_PROXY_HOPS=1` behind a reverse proxy, otherwise all clients appear with the
+  proxy's address and share one lockout counter.
+
+## OpenID Connect
+
+Requirements: `PUBLIC_URL` is set to the external `https://` URL, and the provider allows
+the redirect URI **`<PUBLIC_URL>/auth/callback`**.
+
+The UI uses the authorization code flow with PKCE (`S256`) and a confidential client.
+User name: `OIDC_USERNAME_CLAIM` (default `preferred_username`); groups:
+`OIDC_GROUPS_CLAIM` (default `groups`).
+
+**Always restrict who may sign in** with `OIDC_ALLOWED_GROUPS` and/or
+`OIDC_ALLOWED_USERS` – or with an access policy in the provider. Without either, every
+account that the provider lets use this client can ban IPs (a warning is logged at start).
+
+### Authentik
+
+1. **Applications → Providers → Create → OAuth2/OpenID Provider**
+   - Name: `fail2ban-webui`
+   - Authorization flow: `default-provider-authorization-explicit-consent` (or implicit)
+   - Client type: **Confidential** – note *Client ID* and *Client Secret*
+   - Redirect URIs: `strict` · `https://fail2ban.example.org/auth/callback`
+   - Signing key: any certificate (e.g. `authentik Self-signed Certificate`)
+   - Advanced protocol settings → Scopes: `openid`, `email`, `profile`
+     (the default *profile* mapping contains the `groups` claim)
+2. **Applications → Applications → Create**
+   - Name: `fail2ban-webui`, Slug: `fail2ban-webui`, Provider: the one from step 1
+3. **Directory → Groups → Create** `fail2ban-admins` and add the users.
+4. Optional, recommended: in the application under **Policy / Group / User Bindings**
+   bind the group `fail2ban-admins`, so nobody else even reaches the consent screen.
+5. `.env`:
+
+   ```ini
+   PUBLIC_URL=https://fail2ban.example.org
+   AUTH_MODE=oidc
+   OIDC_ISSUER=https://auth.example.org/application/o/fail2ban-webui/
+   OIDC_CLIENT_ID=…
+   OIDC_CLIENT_SECRET='…'
+   OIDC_ALLOWED_GROUPS=fail2ban-admins
+   OIDC_BUTTON_LABEL=Authentik
+   ```
+
+6. `docker compose up -d`, open `PUBLIC_URL`, click **Sign in with Authentik**.
+
+The issuer URL is shown in Authentik on the provider page (*OpenID Configuration Issuer*).
+
+### Other providers
+
+| Provider | `OIDC_ISSUER` | Groups |
+|---|---|---|
+| Keycloak | `https://kc.example.org/realms/<realm>` | add a *Group Membership* mapper with claim name `groups`, "Full group path" off |
+| Authelia | `https://auth.example.org` | `groups` scope; set `OIDC_SCOPES=openid email profile groups` |
+| Zitadel | `https://<instance>.zitadel.cloud` | roles instead of groups – use `OIDC_ALLOWED_USERS` or a project role check in Zitadel |
+
+### Sign out
+
+"Sign out" ends the session in the web UI. The session at the provider stays active, so
+the next "Sign in with …" usually logs in again without a password.
+
+## Reverse-proxy mode
+
+The proxy does the authentication; the UI only checks where requests come from and,
+optionally, which user the proxy reports.
+
+```ini
+AUTH_MODE=proxy
+TRUSTED_PROXY_HOPS=1
+# only accept requests from the proxy (address as seen by the container)
+AUTH_PROXY_ALLOWED_IPS=172.23.51.1/32
+# optional: user name for the audit log, set by the proxy
+AUTH_PROXY_HEADER=X-authentik-username
+# optional: logout URL of the proxy/IdP
+AUTH_PROXY_LOGOUT_URL=https://fail2ban.example.org/outpost.goauthentik.io/sign_out
+```
+
+- `AUTH_PROXY_ALLOWED_IPS` is checked against the **direct** peer of the container, not
+  against `X-Forwarded-For`. If the proxy runs on the same Docker host and reaches the
+  container via the published port, that is the network gateway (`172.23.51.1` in the
+  example compose file); check with `docker compose logs` after a request.
+- With `AUTH_PROXY_HEADER` set, requests without the header are rejected (401). Make sure
+  the proxy **removes** that header from client requests – forward-auth integrations
+  (Authentik, Authelia) do that.
+- Without `AUTH_PROXY_HEADER` the audit log shows the user `proxy`.
+
+Examples for Nginx Proxy Manager, Traefik and Caddy are in
+[reverse-proxy.md](reverse-proxy.md).