dorfteich/docs/architecture/security.md

# Security concept

Threat-driven summary; detailed mechanics live in the referenced ADRs.

## Assets & main threats

Wiki content (possibly confidential per pond/label), user credentials and
e-mail addresses, instance availability. Threat actors: anonymous internet
(public instance with self-signup), malicious registered users, malicious
or sloppy plugin authors, compromised dependencies.

## Authentication & session security (ADR 0007)

- Argon2id password hashing; opaque server-side sessions in HttpOnly,
  Secure, SameSite=Lax cookies; CSRF protected by SameSite + origin checks
  on mutating requests (double-submit token for the file-download edge
  cases).
- The origin check **fails closed** (issue #189): a cookie-carrying
  mutation without `Origin` and `Referer` (or with an unparsable one) is
  rejected with `403 csrf_origin_mismatch`. Non-browser clients
  authenticate with a PAT/bearer token and no cookie, which never reaches
  the check — the exception is structural, not a header loophole; a
  request that does carry the session cookie is always checked. Scripted
  cookie clients must send `Origin: <APP_BASE_URL>`.
- Session bounds are configurable (issue #190): an absolute lifetime
  (`SESSION_ABSOLUTE_HOURS`, default 7 days, never extended by activity —
  also the cookie `maxAge`) and an idle timeout (`SESSION_IDLE_HOURS`,
  default 3 days), both enforced server-side, the idle bound against
  `lastSeenAt`.
- E-mail verification (double opt-in) before an account can create content;
  password reset via single-use hashed tokens; both rate-limited.
- Rate limiting (DB-backed) on login, signup, reset, and API; lockout
  backoff on repeated failed logins per account+IP.
- Feed tokens (issue #149) authenticate feed URLs via `?token=` — feed
  readers cannot send headers, which is why the credential lives in the
  URL at all. Moving it into a path segment was rejected (issue #191): a
  path lands in the same proxy and request logs as a query string.
  Instead: the instance switch `feeds.enabled` hides the whole feed
  surface with 404 semantics (the VS-NfD reference configuration turns
  feeds off), tokens are stored hashed, and the api's request log masks
  `?token=` values (`common/mask-token-param.ts`), so no code path logs
  the credential.
- Self-registration can be disabled instance-wide; personal-pond quotas
  (editors/readers/ponds/storage) bound the blast radius of spam accounts.

## Authorization

- Single resolution algorithm (`permissions.md`) in `packages/shared`,
  enforced in API guards and at collab token issuance — never in the client.
- Default-closed: no grant → no access. Public access is always an explicit
  grant.
- Admin actions are audit-logged (`operations.md`).

## Content & upload security

- Editor content is structured (ProseMirror schema) — no raw HTML from
  users. The HTML render endpoint escapes everything outside the schema;
  link protocols allowlisted (`https`, `http`, `mailto`).
- Uploads (ADR 0011): MIME/extension allowlist, size limits, magic-byte
  checks, SVG sanitization or rejection, `Content-Disposition: attachment`
  for non-image types, no user content served same-origin as executable
  (`X-Content-Type-Options: nosniff`; uploads path never serves
  `text/html`).
- App CSP (strict): `default-src 'self'`; `font-src 'self'` (ADR 0016);
  no third-party origins at all — the GDPR posture is "zero external
  requests".
- The full-text index holds **no trashed content** (issue #195): trashing
  a page or pond clears the affected `search_vector`s, restore rebuilds
  them, `reindexAll` converges to the same invariant, and a one-off
  migration backfilled pre-existing trash. The query-side
  `deleted_at IS NULL` joins stay in place as the second, independent
  layer — a future query path that forgets them still finds no trashed
  vectors. (The plaintext cache row itself remains until purge; the index
  is the concern here because it is queryable.)

## Security response headers & CORS (issue #197)

Every api response carries this header set, stamped by a hand-rolled
15-line middleware (`apps/api/src/common/security-headers.middleware.ts`)
rather than `helmet` — the set is small enough to own, each value is a
deliberate decision, and the api gains no transitive dependency. It is
wired through the AppModule's `MiddlewareConsumer`, so the e2e harness
boots the exact production middleware.

| Header                      | Value                                                          | Why                                                                                                                                                                                                   |
| --------------------------- | -------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `Strict-Transport-Security` | `max-age=31536000`                                             | One year, **no** `includeSubDomains` — the api cannot speak for sibling subdomains it does not control. Browsers ignore HSTS over plain http, so it is sent unconditionally.                          |
| `X-Content-Type-Options`    | `nosniff`                                                      | No MIME sniffing, anywhere (the uploads path relies on this too, see above).                                                                                                                          |
| `Referrer-Policy`           | `no-referrer`                                                  | Page paths are permission-scoped knowledge; leak them to no destination.                                                                                                                              |
| `X-Frame-Options`           | `SAMEORIGIN`                                                   | Deliberately **not** `DENY`: the plugin sandbox (ADR 0008) embeds `/api/v1/plugins/<id>/<version>/frame` same-origin, and the frame's CSP has no `frame-ancestors` — this header governs its framing. |
| `Permissions-Policy`        | `camera=(), microphone=(), geolocation=(), payment=(), usb=()` | Powerful browser features denied outright; nothing in the app uses them.                                                                                                                              |

**CORS** is a stated decision, not an implicit default: no foreign origin
is granted anything. The middleware echoes `Access-Control-Allow-Origin`
(plus `Allow-Credentials: true`) only for the `APP_BASE_URL` origin
itself — where browsers never consult CORS anyway, since the SPA calls
the api same-origin (the dev server proxies `/api`). The echo documents
the stance rather than enabling a caller; consequently there is no
preflight handling (same-origin requests never preflight), and every
response carries `Vary: Origin` for cache correctness. Cross-origin API
access is cookie-less by design anyway (PAT/Bearer, see Public API), and
non-browser clients are unaffected by CORS.

Regression fence: `apps/api/src/common/security-headers.e2e.test.ts`
(header set, foreign origin gets no ACAO) and the frame assertion in
`plugins.e2e.db.test.ts`. TLS termination itself is the reverse proxy's
job (out of scope, below).

## Plugin sandboxing (ADR 0008, operational)

- Code plugins: opaque-origin iframes, no network (`connect-src 'none'`),
  capability-scoped postMessage API executed with the **viewer's**
  permissions server-side; declared capabilities surfaced to the Site Admin
  at install time.
- Style plugins: CSS sanitized (no `@import`/external `url()`), scoped
  class names.
- Install surface restricted to Site Admins; packages size-limited and
  schema-validated; the `plugins/` directory watcher only trusts the volume
  (host-level access implies game over anyway).

## Collaboration layer

- WebSocket connect requires a short-lived (≤ 60 s) single-purpose JWT
  bound to user + page + mode; write revocation closes sessions via
  LISTEN/NOTIFY (`realtime-collaboration.md`).
- Update size and document size ceilings prevent resource-exhaustion via
  crafted CRDT updates.

## Secrets & configuration

- Secrets (DB password, token root key, SMTP credentials) live only in
  the stage `.env` (mode 600, never in git) and container env — not in the
  database (`instance_settings` stores non-secret config; the SMTP password
  entered in the setup wizard is written to the env-backed secret store,
  not to a DB row).
- Token key hierarchy (ADR 0020, issue #188): `COLLAB_TOKEN_SECRET` is a
  ROOT key. Each token purpose uses its own HKDF-SHA-256 subkey
  (`deriveTokenKey` in `packages/shared/src/token-crypto.ts`): `collab`
  for the collaboration JWTs (signed and verified by `jose`, HS256 as an
  explicit allowlist), `unsubscribe` for the digest unsubscribe links. No
  code path signs with the root key directly, so a compromise of one
  purpose's tokens is not transferable to the other.
- Dual-verify window: unsubscribe links minted before the key separation
  live in already-sent mail (90-day TTL). Verification accepts the legacy
  derivation (root key + purpose prefix) until **2026-11-01**
  (`LEGACY_VERIFY_UNTIL` in `apps/api/src/notifications/unsubscribe-token.ts`),
  after which the legacy path goes dead automatically. New tokens are only
  ever signed with the subkey.
- Key rotation: rotating the root key rotates every derived subkey at once
  (desired: one secret to rotate) via env change plus rolling restart;
  procedure documented in `operations.md` runbooks.
- Dependencies: lockfile-pinned; monthly update batch; images pinned to
  digests in Prod.

## Logging

- Application logs are pino JSON on stdout; `authorization` and `cookie`
  headers are redacted, request bodies are never logged, and feed-token
  query values are masked (issue #191). Log forwarding and retention are
  the container runtime's job (SIEM division of labour — the application
  side of that contract is the stable event catalogue, issue #201).
- The persistent audit trail (`audit_log`, issue #86) records auth and
  admin events — who changed access or configuration, not who edited
  what; content activity stays log-only by design.
- Audit retention (issue #196): entries are kept for
  `audit.retentionDays` (instance setting, default 365) and pruned by the
  daily `audit-retention` job; each pruning run is itself recorded as
  `audit.pruned` with count and cutoff, so a gap in the trail is always
  explainable. The read-access trail (#222–#225) is deliberately not
  covered by this period — it gets its own.

## Privacy (GDPR)

- No external requests from the browser (fonts self-hosted, no CDNs, no
  analytics by default).
- Instance-configurable legal pages (imprint, privacy policy) are a core
  feature; dorfteich.online uses the operator's standard texts.
- Data minimization: username, e-mail, password hash, locale — nothing
  else required. Account deletion: personal pond and authored ponds
  follow the trash/purge path; authorship on shared content is pseudonymized
  ("deleted user"). A data-export endpoint (own profile + own ponds as
  Markdown/ZIP) supports access/portability requests.
- IP addresses appear only in rate-limit counters (short TTL) and reverse
  proxy logs (host-level rotation) — documented in the privacy-policy
  template.

## Out of scope (v1, explicit)

- No end-to-end encryption of page content (server sees plaintext — needed
  for search, export, rendering).
- No plugin marketplace/signing — installation is a deliberate Site Admin
  act of trust in the reviewed package.
- No SSO in MVP (OIDC-ready per ADR 0007).