certctl/docs/operator/security.md

# certctl Security Posture & Operator Guidance

> Last reviewed: 2026-05-10

This document collects the operator-facing security guidance that the source
code's per-finding comment blocks reference. Each section names the audit
finding it closes, the threat model, and the operator action required (if
any).

## OCSP responder availability

**Audit reference:** Bundle C / M-020. CWE-770 (uncontrolled resource
consumption); RFC 6960 (OCSP); RFC 7633 (Must-Staple).

certctl ships an OCSP responder at `/.well-known/pki/ocsp/{issuer_id}/{serial}`
that signs a fresh response per request. Pre-Bundle-C the unauth handler
chain had no rate limit, so an attacker could DoS the responder and force
fail-open relying parties to accept revoked certificates as valid. Bundle C
adds the same per-key rate limiter to the unauth chain that the authenticated
chain has used since Bundle B. Per-IP keying applies because OCSP traffic is
unauthenticated.

The rate limiter alone does not solve the underlying revocation-bypass risk.
**The architectural fix is for issued certificates to carry the OCSP
Must-Staple TLS Feature extension** (RFC 7633, OID 1.3.6.1.5.5.7.1.24). When
present, conforming TLS clients refuse to negotiate a session unless the
server staples a fresh signed OCSP response in the TLS handshake. This shifts
revocation enforcement from the client's discretion (which most fail-open by
default) to a hard requirement that the connection cannot complete without
proof of non-revocation.

### Operator action

For certificates issued to systems where revocation correctness matters:

1. **Configure the issuer profile to set `must-staple: true`.** Out-of-the-box
   profiles in `migrations/seed.sql` do not set this; operators add it at
   profile-creation time via the API or by editing seed data.
2. **Confirm the relying party honors the extension.** OpenSSL ≥ 1.1.0,
   Firefox, and Chrome 84+ all enforce Must-Staple. Older clients silently
   ignore it.
3. **Confirm the deployment target is configured for OCSP stapling** so the
   server can actually deliver the stapled response in the handshake.
 - **nginx:** `ssl_stapling on; ssl_stapling_verify on;`
 - **Apache:** `SSLUseStapling on`
 - **HAProxy:** `set ssl ocsp-response /path/to/response.der`
 - **Envoy:** `ocsp_staple_policy: must_staple`

### What this does NOT cover

- **CRL fallback.** Must-Staple does not affect CRL behavior. Operators with
  CRL-based relying parties should use the rate-limit + caching defense
  alone; there is no client-side equivalent to Must-Staple for CRLs.
- **Self-issued certs in air-gapped networks.** When the relying party
  cannot reach the OCSP responder at all (the threat model the audit
  cited), Must-Staple is the only mechanism that closes the bypass. CRL
  distribution similarly requires the relying party to fetch the CRL,
  which is also subject to the same network-availability concern.

## Postgres transport encryption

See [docs/database-tls.md](database-tls.md). Bundle B / M-018.

## Encryption at rest

Bundle B / M-001. PBKDF2-SHA256 at 600,000 rounds (OWASP 2024 Password
Storage Cheat Sheet floor) for the operator-supplied passphrase that
derives the AES-256-GCM key for sensitive config columns. v3 blob format
with a per-ciphertext random salt; v1/v2 read fallback for legacy rows.
See [internal/crypto/encryption.go](../../internal/crypto/encryption.go) and
the accompanying tests for the format spec.

## Authentication surface

Bundle B / M-002. Two layers decide auth-exempt status:

1. **Router layer:** `internal/api/router/router.go::AuthExemptRouterRoutes`
 - the endpoints registered via direct `r.mux.Handle` without going
   through the middleware chain (`/health`, `/ready`, `/api/v1/auth/info`,
   `/api/v1/version`, plus `/api/v1/auth/bootstrap` GET + POST per
   Bundle 1 Phase 6).
2. **Dispatch layer:** `internal/api/router/router.go::AuthExemptDispatchPrefixes`
 - URL-prefix routing in `cmd/server/main.go::buildFinalHandler` for
   `/.well-known/pki/*`, `/.well-known/est/*`, `/.well-known/est-mtls`,
   and `/scep[/...]*` (incl. `/scep-mtls`).

Both lists have AST-walking regression tests (`auth_exempt_test.go`) that
fail CI if a new bypass lands without updating the documented constant.

### RBAC primitive (Bundle 1)

Bundle 1 ships role-based authorization on top of API-key
authentication. Every gated handler routes through the
`auth.RequirePermission` middleware (or its router-level wrap
`rbacGate`); the middleware resolves the actor's effective
permissions via the service-layer `Authorizer.CheckPermission`
and returns HTTP 403 BEFORE the handler body runs on miss. The
seven default roles (`admin` / `operator` / `viewer` / `agent` /
`mcp` / `cli` / `auditor`), 33-permission canonical catalogue,
and the auditor split (`r-auditor` holds only `audit.read` +
`audit.export`) are seeded by migration 000029.

For the operator how-to, see [`rbac.md`](rbac.md). For the
threat model + compliance mapping, see
[`auth-threat-model.md`](auth-threat-model.md). For the upgrade
flow from a pre-Bundle-1 deployment, see
[`docs/migration/api-keys-to-rbac.md`](../migration/api-keys-to-rbac.md).

### Day-0 admin bootstrap (Bundle 1 Phase 6)

Fresh deployments where no admin actor exists yet can mint the
first admin via `POST /api/v1/auth/bootstrap` - set
`CERTCTL_BOOTSTRAP_TOKEN`, POST a single curl with the token, and
the server returns the plaintext key value once. The token is
constant-time-compared; the strategy is one-shot via mutex; the
admin-existence probe re-closes the path once an admin lands.
The token is NEVER logged. The minted plaintext key flows only
into the HTTP response body. See
[`rbac.md`](rbac.md#day-0-bootstrap-first-admin-path) for the
full flow.

### Approval-bypass closure (Bundle 1 Phase 9)

`CertificateProfile.RequiresApproval=true` profiles route both
issuance/renewal AND profile edits through the
`ApprovalService` two-person integrity gate (Phase 9 closes the
flip-flop loophole where an admin could disable approval, mutate,
re-enable). Same-actor self-approve is rejected at the service
layer with `ErrApproveBySameActor`. See
[`docs/reference/profiles.md`](../reference/profiles.md) for the
full gate semantics.

### OIDC federation (Bundle 2 Phases 1-7)

Bundle 2 adds OIDC SSO on top of the API-key + RBAC foundation.
Operators configure one or more identity providers (Keycloak,
Authentik, Okta, Auth0, Entra ID, or Google Workspace via Keycloak
broker); end users sign in at the IdP, certctl validates the
returned ID token, and a session cookie is minted.

The token-validation pipeline pins:

- Algorithm allow-list: RS256 / RS512 / ES256 / ES384 / EdDSA only.
  HS256 / HS384 / HS512 / `none` are rejected at the service-layer
  sentinel level.
- IdP-downgrade-attack defense at provider creation AND every
  RefreshKeys: the IdP's advertised
  `id_token_signing_alg_values_supported` is intersected with the
  allow-list; a provider that advertises HS-family is rejected
  before any token is signed under the weak alg.
- Exact `iss` match (`ErrIssuerMismatch`).
- `aud` membership + `azp` for multi-aud tokens (per OIDC core
  §3.1.3.7 step 5).
- `at_hash` REQUIRED-when-access_token-present (Phase 3 tightening
  of the spec MAY → MUST so a substituted access token cannot
  ride alongside a clean ID token).
- Single-use state + nonce (32-byte random server-generated;
  atomic `DELETE...RETURNING` on consume).
- PKCE-S256 mandatory; `plain` rejected.
- Configurable `iat` window (default 300s, capped 600s).
- JWKS cache with operator-triggered RefreshKeys + auto-refresh on
  TTL expiry (default 3600s); JWKS-fetch failure during a key
  rotation returns 503 to the in-flight login (existing sessions
  untouched).

OIDC `client_secret` is encrypted at rest via AES-256-GCM (v3 blob
format: magic 0x03 + salt(16) + nonce(12) + ciphertext+tag) using
the `CERTCTL_CONFIG_ENCRYPTION_KEY` passphrase. The encryption
invariant is pinned by an integration test
(`internal/repository/postgres/oidc_encryption_invariant_test.go`)
that asserts ciphertext != plaintext + correct blob shape +
round-trip recovery + wrong-passphrase fails.

Per-IdP setup guides at
[`oidc-runbooks/index.md`](oidc-runbooks/index.md) cover Keycloak,
Authentik, Okta, Auth0, Entra ID, and Google Workspace.

### Sessions + back-channel logout (Bundle 2 Phases 4-6)

Successful OIDC login mints a session cookie:
`v1.<session_id>.<signing_key_id>.<base64url-no-pad(HMAC-SHA256)>`.
The HMAC input is **length-prefixed** as `len:sid:len:kid` to defeat
concatenation-collision attacks on bare-concat designs. Cookie
attributes:

- `HttpOnly=true` (no JS access; defends XSS cookie theft).
- `Secure=true` (HTTPS-only; defends network MITM).
- `SameSite=Lax` default (configurable to Strict via
  `CERTCTL_SESSION_SAMESITE`).
- `Path=/`, host-only.

Idle timeout default 1h; absolute timeout default 8h; both
configurable via `CERTCTL_SESSION_IDLE_TIMEOUT` and
`CERTCTL_SESSION_ABSOLUTE_TIMEOUT`. The scheduler's
`sessionGCLoop` (default 1h interval) sweeps expired rows.

CSRF defense: plaintext CSRF token in the JS-readable
`certctl_csrf` cookie (intentionally `HttpOnly=false` for the GUI
to echo into the `X-CSRF-Token` header); SHA-256 hash on the
session row; `subtle.ConstantTimeCompare` in `CSRFMiddleware`.
API-key actors are CSRF-exempt (no session row in context).

Session signing keys rotate via `RotateSigningKey`; the old key
stays valid for `CERTCTL_SESSION_SIGNING_KEY_RETENTION` (default
24h) so existing cookies validate during rollover. Past retention,
the old key's row is dropped and any cookie still signed under it
returns `ErrSigningKeyNotFound`. `EnsureInitialSigningKey` is
fail-fatal at server boot.

Back-channel logout per **OpenID Connect Back-Channel Logout 1.0**
(NOT RFC 8414): `POST /auth/oidc/back-channel-logout` accepts a
JWT-signed logout token from the IdP, validates the JWT against
the IdP's JWKS (same alg allow-list as login), pins required
claims (`iss` / `aud` / `iat` / `jti` / `events`; exactly one of
`sub` / `sid`; `nonce` MUST be absent), defeats replay via
`jti`-based deduplication, and revokes matching sessions.

For threat-model coverage of these surfaces, see
[`auth-threat-model.md`](auth-threat-model.md). For the
operator-runnable performance baselines, see
[`auth-benchmarks.md`](auth-benchmarks.md).

### OIDC first-admin bootstrap (Bundle 2 Phase 7)

Coexists with Bundle 1's env-var-token bootstrap. When the
operator sets `CERTCTL_BOOTSTRAP_ADMIN_GROUPS` + (optionally)
`CERTCTL_BOOTSTRAP_OIDC_PROVIDER_ID`, the first user with one of
those IdP groups becomes admin on first login per tenant.
Subsequent users go through normal mapping. The admin-existence
probe ensures only one wins between the two bootstrap paths;
once any actor holds `r-admin`, the OIDC bootstrap hook silently
falls through to normal mapping. Audit row on every grant
(`bootstrap.oidc_first_admin`, `event_category=auth`).

### Break-glass admin (Bundle 2 Phase 7.5)

Default-OFF (`CERTCTL_BREAKGLASS_ENABLED=false`). When enabled,
the local-password admin path bypasses OIDC + group-claim layers;
intended ONLY for SSO-broken incidents.

- Argon2id with OWASP 2024 params (m=64 MiB, t=3, p=4, 16-byte
  salt, 32-byte output, per-password random salt, PHC-format
  hash). Hash column is `json:"-"` so handlers cannot wire-leak.
- Lockout state machine: 5 failures (default; configurable via
  `CERTCTL_BREAKGLASS_LOCKOUT_THRESHOLD`) within 1h reset window
  (`_LOCKOUT_RESET_INTERVAL`) trips a 30s lockout (`_LOCKOUT_DURATION`).
  Atomic single-statement IncrementFailure defeats concurrent
  racing attempts.
- Constant-time across all failure paths via `verifyDummy()` —
  wrong-password / locked-account / no-actor all take statistically
  indistinguishable time.
- Surface invisibility: when disabled, ALL four endpoints return
  HTTP 404 (NOT 403). Scanners cannot distinguish "endpoint
  disabled" from "endpoint doesn't exist".
- WARN log at server boot when `ENABLED=true`; audit row on every
  break-glass login (`auth.breakglass_login_*`,
  `event_category=auth`); WebAuthn/FIDO2 second factor pairing
  on the v3 roadmap (Decision 12).

Operator should DISABLE break-glass within 24h of SSO recovery
to avoid a permanent backdoor; the runbook at
[`auth-threat-model.md#break-glass-risks-phase-75`](auth-threat-model.md)
documents the full state machine.

### Migrating an existing deployment to OIDC

A Bundle-1-merged deployment that wants to add OIDC follows the
step-by-step at
[`docs/migration/oidc-enable.md`](../migration/oidc-enable.md):
configure CERTCTL_CONFIG_ENCRYPTION_KEY, pick + configure an IdP
per the relevant runbook, configure the certctl-side OIDCProvider
+ group→role mappings, verify the login flow against a single
test user, then announce the SSO endpoint to the rest of the
organization.

## Per-user rate limiting

Bundle B / M-025. Authenticated callers are bucketed by API-key name;
unauthenticated callers (probes, OCSP relying parties, EST/SCEP enrollees)
are bucketed by source IP. `RPS` and `BurstSize` are per-key budgets.
`PerUserRPS` / `PerUserBurstSize` give authenticated clients a separate
budget when set non-zero.

## API key rotation

**Audit reference:** L-004. CWE-924 (improper enforcement of message integrity during transmission in a communication channel) - operator UX variant.

certctl's API keys are configured via the `CERTCTL_API_KEYS_NAMED` env var
(format `name1:key1,name2:key2:admin`) and parsed at startup into an
in-memory list. There is no DB-resident key store, no GUI, no `/api/v1/keys`
endpoint - the env var IS the key inventory.

Pre-Bundle-G the env var rejected duplicate names, so rotating a key
required: stop accepting OLDKEY → restart → roll NEWKEY out. Any client
polling against OLDKEY during the restart window hit a 401.

Bundle G adds a **double-key rotation window**: two entries can share a
name during the rollover, and both keys validate. Operators run the
rotation as:

1. **Generate the new key.** `openssl rand -hex 32` produces a 256-bit
   value with sufficient entropy.

2. **Append the new entry to `CERTCTL_API_KEYS_NAMED`** alongside the
   existing one:
   ```
   CERTCTL_API_KEYS_NAMED="alice:OLDKEY:admin,alice:NEWKEY:admin"
   ```
   Both entries MUST carry the same admin flag - startup fails loud if
   they don't (a non-admin shouldn't share an identity with an admin).

3. **Restart certctl.** A startup INFO log confirms the rotation window
   is active:
   ```
   INFO api-key rotation window active name=alice entries=2 see=docs/security.md::api-key-rotation
   ```

4. **Roll the new key out to all clients.** Both keys validate during
   this phase. Audit-trail actor + per-user rate-limit bucket stay
   consistent across the rollover (both entries produce the same
   `UserKey` context value, the shared name).

5. **Remove the old entry** from `CERTCTL_API_KEYS_NAMED`:
   ```
   CERTCTL_API_KEYS_NAMED="alice:NEWKEY:admin"
   ```

6. **Restart certctl.** OLDKEY now fails with 401. Rotation complete.

The rotation window has no operator-set timeout - it lasts for as long
as both entries are in the env var. Best practice is a 24-72h window
covering a full deploy cadence; if a client hasn't rolled to NEWKEY by
the end of step 4, extend the window before step 5.

### What the contract guarantees

- Two entries with the same `name`: **allowed** if both have the same
  `admin` flag.
- Two entries with the same `name` but mismatched admin: **rejected at
  startup** (privilege escalation guard).
- Two entries with the same `(name, key)` pair: **rejected at startup**
  (typo guard - rotation requires DIFFERENT keys under the same name).
- Single-entry steady state: unchanged from pre-Bundle-G behavior.

### What the contract does NOT do

- **No automatic expiration of OLDKEY.** The operator removes the entry
  in step 5; certctl doesn't track timestamps. A future enhancement
  could add a `rotated_at` annotation if operators ask for it.
- **No GUI / API for key management.** Keys are env-var only by design;
  building a key-management surface is a separate feature project.
- **No revocation list.** If a key leaks, the only path is to remove it
  from the env var and restart. That's appropriate for a small env-var
  inventory; it would not scale to a per-user-key-issued model.

## Reporting a vulnerability

Email `certctl@proton.me`. Coordinated disclosure preferred; we will
acknowledge within 72h.