git.stella-ops.org/docs/modules/authority/architecture.md

# component_architecture_authority.md — **Stella Ops Authority** (2025Q4)

> Consolidates identity and tenancy requirements documented across the AOC, Policy, and Platform guides, along with the dedicated Authority implementation plan.

> **Scope.** Implementation‑ready architecture for **Stella Ops Authority**: the on‑prem **OIDC/OAuth2** service that issues **short‑lived, sender‑constrained operational tokens (OpToks)** to first‑party services and tools. Covers protocols (DPoP & mTLS binding), token shapes, endpoints, storage, rotation, HA, RBAC, audit, and testing. This component is the trust anchor for *who* is calling inside a Stella Ops installation. (Entitlement is proven separately by **PoE** from the cloud Licensing Service; Authority does not issue PoE.)

---

## 0) Mission & boundaries

**Mission.** Provide **fast, local, verifiable** authentication for Stella Ops microservices and tools by minting **very short‑lived** OAuth2/OIDC tokens that are **sender‑constrained** (DPoP or mTLS‑bound). Support RBAC scopes, multi‑tenant claims, and deterministic validation for APIs (Scanner, Signer, Attestor, Excititor, Concelier, UI, CLI, Zastava).

**Boundaries.**

* Authority **does not** validate entitlements/licensing. That’s enforced by **Signer** using **PoE** with the cloud Licensing Service.
* Authority tokens are **operational only** (2–5 min TTL) and must not be embedded in long‑lived artifacts or stored in SBOMs.
* Authority is **stateless for validation** (JWT) and **optional introspection** for services that prefer online checks.

---

## 1) Protocols & cryptography

* **OIDC Discovery**: `/.well-known/openid-configuration`
* **OAuth2** grant types:

  * **Client Credentials** (service↔service, with mTLS or private_key_jwt)
  * **Device Code** (CLI login on headless agents; optional)
  * **Authorization Code + PKCE** (browser login for UI; optional)
* **Sender constraint options** (choose per caller or per audience):

  * **DPoP** (Demonstration of Proof‑of‑Possession): proof JWT on each HTTP request, bound to the access token via `cnf.jkt`.
  * **OAuth 2.0 mTLS** (certificate‑bound tokens): token bound to client certificate thumbprint via `cnf.x5t#S256`.
* **Signing algorithms**: **EdDSA (Ed25519)** preferred; fallback **ES256 (P‑256)**. Rotation is supported via **kid** in JWKS.
* **Token format**: **JWT** access tokens (compact), optionally opaque reference tokens for services that insist on introspection.
* **Clock skew tolerance**: ±60 s; issue `nbf`, `iat`, `exp` accordingly.

---

## 2) Token model

### 2.1 Access token (OpTok) — short‑lived (120–300 s)

**Registered claims**

```
iss   = https://authority.<domain>
sub   = <client_id or user_id>
aud   = <service audience: signer|scanner|attestor|concelier|excititor|ui|zastava>
exp   = <unix ts>  (<= 300 s from iat)
iat   = <unix ts>
nbf   = iat - 30
jti   = <uuid>
scope = "scanner.scan scanner.export signer.sign ..."
```

**Sender‑constraint (`cnf`)**

* **DPoP**:

  ```json
  "cnf": { "jkt": "<base64url(SHA-256(JWK))>" }
  ```
* **mTLS**:

  ```json
  "cnf": { "x5t#S256": "<base64url(SHA-256(client_cert_der))>" }
  ```

**Install/tenant context (custom claims)**

```
tid          = <tenant id>               // multi-tenant
inst         = <installation id>        // unique installation
roles        = [ "svc.scanner", "svc.signer", "ui.admin", ... ]
plan?        = <plan name>              // optional hint for UIs; not used for enforcement
```

> **Note**: Do **not** copy PoE claims into OpTok; OpTok ≠ entitlement. Only **Signer** checks PoE.

### 2.2 Refresh tokens (optional)

* Default **disabled**. If enabled (for UI interactive logins), pair with **DPoP‑bound** refresh tokens or **mTLS** client sessions; short TTL (≤ 8 h), rotating on use (replay‑safe).

### 2.3 ID tokens (optional)

* Issued for UI/browser OIDC flows (Authorization Code + PKCE); not used for service auth.

---

## 3) Endpoints & flows

### 3.1 OIDC discovery & keys

* `GET /.well-known/openid-configuration` → endpoints, algs, jwks_uri
* `GET /jwks` → JSON Web Key Set (rotating, at least 2 active keys during transition)

### 3.2 Token issuance

* `POST /oauth/token`

  * **Client Credentials** (service→service):

    * **mTLS**: mutual TLS + `client_id` → bound token (`cnf.x5t#S256`)
      * `security.senderConstraints.mtls.enforceForAudiences` forces the mTLS path when requested `aud`/`resource` values intersect high-value audiences (defaults include `signer`). Authority rejects clients attempting to use DPoP/basic secrets for these audiences.
      * Stored `certificateBindings` are authoritative: thumbprint, subject, issuer, serial number, and SAN values are matched against the presented certificate, with rotation grace applied to activation windows. Failures surface deterministic error codes (e.g. `certificate_binding_subject_mismatch`).
    * **private_key_jwt**: JWT‑based client auth + **DPoP** header (preferred for tools and CLI)
  * **Device Code** (CLI): `POST /oauth/device/code` + `POST /oauth/token` poll
  * **Authorization Code + PKCE** (UI): standard

**DPoP handshake (example)**

1. Client prepares **JWK** (ephemeral keypair).
2. Client sends **DPoP proof** header with fields:

   ```
   htm=POST
   htu=https://authority.../oauth/token
   iat=<now>
   jti=<uuid>
   ```

   signed with the DPoP private key; header carries JWK.
3. Authority validates proof; issues access token with `cnf.jkt=<thumbprint(JWK)>`.
4. Client uses the same DPoP key to sign **every subsequent API request** to services (Signer, Scanner, …).

**mTLS flow**

* Mutual TLS at the connection; Authority extracts client cert, validates chain; token carries `cnf.x5t#S256`.

### 3.3 Introspection & revocation (optional)

* `POST /oauth/introspect` → `{ active, sub, scope, aud, exp, cnf, ... }`
* `POST /oauth/revoke` → revokes refresh tokens or opaque access tokens.
* **Replay prevention**: maintain **DPoP `jti` cache** (TTL ≤ 10 min) to reject duplicate proofs when services supply DPoP nonces (Signer requires nonce for high‑value operations).

### 3.4 UserInfo (optional for UI)

* `GET /userinfo` (ID token context).

---

## 4) Audiences, scopes & RBAC

### 4.1 Audiences

* `signer` — only the **Signer** service should accept tokens with `aud=signer`.
* `attestor`, `scanner`, `concelier`, `excititor`, `ui`, `zastava` similarly.

Services **must** verify `aud` and **sender constraint** (DPoP/mTLS) per their policy.

### 4.2 Core scopes

| Scope                              | Service            | Operation                  |
| ---------------------------------- | ------------------ | -------------------------- |
| `signer.sign`                      | Signer             | Request DSSE signing       |
| `attestor.write`                   | Attestor           | Submit Rekor entries       |
| `scanner.scan`                     | Scanner.WebService | Submit scan jobs           |
| `scanner.export`                   | Scanner.WebService | Export SBOMs               |
| `scanner.read`                     | Scanner.WebService | Read catalog/SBOMs         |
| `vex.read` / `vex.admin`           | Excititor              | Query/operate              |
| `concelier.read` / `concelier.export`  | Concelier            | Query/exports              |
| `ui.read` / `ui.admin`             | UI                 | View/admin                 |
| `zastava.emit` / `zastava.enforce` | Scanner/Zastava    | Runtime events / admission |

**Roles → scopes mapping** is configured centrally (Authority policy) and pushed during token issuance.

---

## 5) Storage & state

* **Configuration DB** (PostgreSQL/MySQL): clients, audiences, role→scope maps, tenant/installation registry, device code grants, persistent consents (if any).
* **Cache** (Redis):

  * DPoP **jti** replay cache (short TTL)
  * **Nonce** store (per resource server, if they demand nonce)
  * Device code pollers, rate limiting buckets
* **JWKS**: key material in HSM/KMS or encrypted at rest; JWKS served from memory.

---

## 6) Key management & rotation

* Maintain **at least 2 signing keys** active during rotation; tokens carry `kid`.
* Prefer **Ed25519** for compact tokens; maintain **ES256** fallback for FIPS contexts.
* Rotation cadence: 30–90 days; emergency rotation supported.
* Publish new JWKS **before** issuing tokens with the new `kid` to avoid cold‑start validation misses.
* Keep **old keys** available **at least** for max token TTL + 5 minutes.

---

## 7) HA & performance

* **Stateless issuance** (except device codes/refresh) → scale horizontally behind a load‑balancer.
* **DB** only for client metadata and optional flows; token checks are JWT‑local; introspection endpoints hit cache/DB minimally.
* **Targets**:

  * Token issuance P95 ≤ **20 ms** under warm cache.
  * DPoP proof validation ≤ **1 ms** extra per request at resource servers (Signer/Scanner).
  * 99.9% uptime; HPA on CPU/latency.

---

## 8) Security posture

* **Strict TLS** (1.3 preferred); HSTS; modern cipher suites.
* **mTLS** enabled where required (Signer/Attestor paths).
* **Replay protection**: DPoP `jti` cache, nonce support for **Signer** (add `DPoP-Nonce` header on 401; clients re‑sign).
* **Rate limits** per client & per IP; exponential backoff on failures.
* **Secrets**: clients use **private_key_jwt** or **mTLS**; never basic secrets over the wire.
* **CSP/CSRF** hardening on UI flows; `SameSite=Lax` cookies; PKCE enforced.
* **Logs** redact `Authorization` and DPoP proofs; store `sub`, `aud`, `scopes`, `inst`, `tid`, `cnf` thumbprints, not full keys.

---

## 9) Multi‑tenancy & installations

* **Tenant (`tid`)** and **Installation (`inst`)** registries define which audiences/scopes a client can request.
* Cross‑tenant isolation enforced at issuance (disallow rogue `aud`), and resource servers **must** check that `tid` matches their configured tenant.

---

## 10) Admin & operations APIs

All under `/admin` (mTLS + `authority.admin` scope).

```
POST /admin/clients                 # create/update client (confidential/public)
POST /admin/audiences               # register audience resource URIs
POST /admin/roles                   # define role→scope mappings
POST /admin/tenants                 # create tenant/install entries
POST /admin/keys/rotate             # rotate signing key (zero-downtime)
GET  /admin/metrics                 # Prometheus exposition (token issue rates, errors)
GET  /admin/healthz|readyz          # health/readiness
```

Declared client `audiences` flow through to the issued JWT `aud` claim and the token request's `resource` indicators. Authority relies on this metadata to enforce DPoP nonce challenges for `signer`, `attestor`, and other high-value services without requiring clients to repeat the audience parameter on every request.

---

## 11) Integration hard lines (what resource servers must enforce)

Every Stella Ops service that consumes Authority tokens **must**:

1. Verify JWT signature (`kid` in JWKS), `iss`, `aud`, `exp`, `nbf`.
2. Enforce **sender‑constraint**:

   * **DPoP**: validate DPoP proof (`htu`, `htm`, `iat`, `jti`) and match `cnf.jkt`; cache `jti` for replay defense; honor nonce challenges.
   * **mTLS**: match presented client cert thumbprint to token `cnf.x5t#S256`.
3. Check **scopes**; optionally map to internal roles.
4. Check **tenant** (`tid`) and **installation** (`inst`) as appropriate.
5. For **Signer** only: require **both** OpTok and **PoE** in the request (enforced by Signer, not Authority).

---

## 12) Error surfaces & UX

* Token endpoint errors follow OAuth2 (`invalid_client`, `invalid_grant`, `invalid_scope`, `unauthorized_client`).
* Resource servers use RFC 6750 style (`WWW-Authenticate: DPoP error="invalid_token", error_description="…", dpop_nonce="…" `).
* For DPoP nonce challenges, clients retry with the server‑supplied nonce once.

---

## 13) Observability & audit

* **Metrics**:

  * `authority.tokens_issued_total{grant,aud}`
  * `authority.dpop_validations_total{result}`
  * `authority.mtls_bindings_total{result}`
  * `authority.jwks_rotations_total`
  * `authority.errors_total{type}`
* **Audit log** (immutable sink): token issuance (`sub`, `aud`, `scopes`, `tid`, `inst`, `cnf thumbprint`, `jti`), revocations, admin changes.
* **Tracing**: token flows, DB reads, JWKS cache.

---

## 14) Configuration (YAML)

```yaml
authority:
  issuer: "https://authority.internal"
  signing:
    enabled: true
    activeKeyId: "authority-signing-2025"
    keyPath: "../certificates/authority-signing-2025.pem"
    algorithm: "ES256"
    keySource: "file"
  security:
    rateLimiting:
      token:
        enabled: true
        permitLimit: 30
        window: "00:01:00"
        queueLimit: 0
      authorize:
        enabled: true
        permitLimit: 60
        window: "00:01:00"
        queueLimit: 10
      internal:
        enabled: false
        permitLimit: 5
        window: "00:01:00"
        queueLimit: 0
    senderConstraints:
      dpop:
        enabled: true
        allowedAlgorithms: [ "ES256", "ES384" ]
        proofLifetime: "00:02:00"
        allowedClockSkew: "00:00:30"
        replayWindow: "00:05:00"
        nonce:
          enabled: true
          ttl: "00:10:00"
          maxIssuancePerMinute: 120
          store: "redis"
          redisConnectionString: "redis://authority-redis:6379?ssl=false"
          requiredAudiences:
            - "signer"
            - "attestor"
      mtls:
        enabled: true
        requireChainValidation: true
        rotationGrace: "00:15:00"
        enforceForAudiences:
          - "signer"
        allowedSanTypes:
          - "dns"
          - "uri"
        allowedCertificateAuthorities:
          - "/etc/ssl/mtls/clients-ca.pem"
  clients:
    - clientId: scanner-web
      grantTypes: [ "client_credentials" ]
      audiences: [ "scanner" ]
      auth: { type: "private_key_jwt", jwkFile: "/secrets/scanner-web.jwk" }
      senderConstraint: "dpop"
      scopes: [ "scanner.scan", "scanner.export", "scanner.read" ]
    - clientId: signer
      grantTypes: [ "client_credentials" ]
      audiences: [ "signer" ]
      auth: { type: "mtls" }
      senderConstraint: "mtls"
      scopes: [ "signer.sign" ]
    - clientId: notify-web-dev
      grantTypes: [ "client_credentials" ]
      audiences: [ "notify.dev" ]
      auth: { type: "client_secret", secretFile: "/secrets/notify-web-dev.secret" }
      senderConstraint: "dpop"
      scopes: [ "notify.read", "notify.admin" ]
    - clientId: notify-web
      grantTypes: [ "client_credentials" ]
      audiences: [ "notify" ]
      auth: { type: "client_secret", secretFile: "/secrets/notify-web.secret" }
      senderConstraint: "dpop"
      scopes: [ "notify.read", "notify.admin" ]
```

---

## 15) Testing matrix

* **JWT validation**: wrong `aud`, expired `exp`, skewed `nbf`, stale `kid`.
* **DPoP**: invalid `htu`/`htm`, replayed `jti`, stale `iat`, wrong `jkt`, nonce dance.
* **mTLS**: wrong client cert, wrong CA, thumbprint mismatch.
* **RBAC**: scope enforcement per audience; over‑privileged client denied.
* **Rotation**: JWKS rotation while load‑testing; zero‑downtime verification.
* **HA**: kill one Authority instance; verify issuance continues; JWKS served by peers.
* **Performance**: 1k token issuance/sec on 2 cores with Redis enabled for jti caching.

---

## 16) Threat model & mitigations (summary)

| Threat              | Vector           | Mitigation                                                                                 |
| ------------------- | ---------------- | ------------------------------------------------------------------------------------------ |
| Token theft         | Copy of JWT      | **Short TTL**, **sender‑constraint** (DPoP/mTLS); replay blocked by `jti` cache and nonces |
| Replay across hosts | Reuse DPoP proof | Enforce `htu`/`htm`, `iat` freshness, `jti` uniqueness; services may require **nonce**     |
| Impersonation       | Fake client      | mTLS or `private_key_jwt` with pinned JWK; client registration & rotation                  |
| Key compromise      | Signing key leak | HSM/KMS storage, key rotation, audit; emergency key revoke path; narrow token TTL          |
| Cross‑tenant abuse  | Scope elevation  | Enforce `aud`, `tid`, `inst` at issuance and resource servers                              |
| Downgrade to bearer | Strip DPoP       | Resource servers require DPoP/mTLS based on `aud`; reject bearer without `cnf`             |

---

## 17) Deployment & HA

* **Stateless** microservice, containerized; run ≥ 2 replicas behind LB.
* **DB**: HA Postgres (or MySQL) for clients/roles; **Redis** for device codes, DPoP nonces/jtis.
* **Secrets**: mount client JWKs via K8s Secrets/HashiCorp Vault; signing keys via KMS.
* **Backups**: DB daily; Redis not critical (ephemeral).
* **Disaster recovery**: export/import of client registry; JWKS rehydrate from KMS.
* **Compliance**: TLS audit; penetration testing for OIDC flows.

---

## 18) Implementation notes

* Reference stack: **.NET 10** + **OpenIddict 6** (or IdentityServer if licensed) with custom DPoP validator and mTLS binding middleware.
* Keep the DPoP/JTI cache pluggable; allow Redis/Memcached.
* Provide **client SDKs** for C# and Go: DPoP key mgmt, proof generation, nonce handling, token refresh helper.

---

## 19) Quick reference — wire examples

**Access token (payload excerpt)**

```json
{
  "iss": "https://authority.internal",
  "sub": "scanner-web",
  "aud": "signer",
  "exp": 1760668800,
  "iat": 1760668620,
  "nbf": 1760668620,
  "jti": "9d9c3f01-6e1a-49f1-8f77-9b7e6f7e3c50",
  "scope": "signer.sign",
  "tid": "tenant-01",
  "inst": "install-7A2B",
  "cnf": { "jkt": "KcVb2V...base64url..." }
}
```

**DPoP proof header fields (for POST /sign/dsse)**

```json
{
  "htu": "https://signer.internal/sign/dsse",
  "htm": "POST",
  "iat": 1760668620,
  "jti": "4b1c9b3c-8a95-4c58-8a92-9c6cfb4a6a0b"
}
```

Signer validates that `hash(JWK)` in the proof matches `cnf.jkt` in the token.

---

## 20) Rollout plan

1. **MVP**: Client Credentials (private_key_jwt + DPoP), JWKS, short OpToks, per‑audience scopes.
2. **Add**: mTLS‑bound tokens for Signer/Attestor; device code for CLI; optional introspection.
3. **Hardening**: DPoP nonce support; full audit pipeline; HA tuning.
4. **UX**: Tenant/installation admin UI; role→scope editors; client bootstrap wizards.