Architecture

This document describes the components, authorization model, and design of the celine-policies repository.

Components

The repository contains four main pieces:

1. MQTT Auth Service

A FastAPI application (src/celine/mqtt_auth/) that acts as the HTTP backend for mosquitto-go-auth. Mosquitto delegates authentication and authorization decisions to this service over HTTP.

The service uses celine-sdk's PolicyEngine (built on regorus, a Rust OPA implementation) to evaluate Rego policies at request time. An optional in-memory decision cache (CachedPolicyEngine) reduces repeated evaluations.

Endpoints: /user (auth), /acl (topic access), /superuser (admin check), /health.

2. Provisioning Service

A FastAPI application (src/celine/provisioning/) that is the only thing that writes a participant account into the celine realm. keycloak sync-users calls the same package; ../onboarding calls the service and holds no Keycloak grant of its own. It is the only client granted a provisioning.* scope: onboarding is the single point of access to the provisioner.

Endpoints: PUT /participants/{community}/{key} (ensure the account, its REC organization and its org group, and optionally invite the person), POST /participants/{community}/{key}/invitation (email an invitation or a password reset, as the body's intent names), POST /participants/{community}/{key}/disable, POST /reconcile/{community}, /health.

No password is ever generated, returned or emailed. Keycloak sends every email, through execute-actions-email, and the person sets their own password from the link. The service decides only whether to ask for one and for how long it lasts — see celine.provisioning.invitation and the API reference.

It is stateless — a retry is another PUT, and idempotency comes from the keys — and it authorises by provisioning.* scopes like every other service.

It holds realm-wide Keycloak administration (manage-users + manage-realm), which is what makes organization membership possible at all: no fine-grained permission expresses the Organizations API. The grant is acceptable only because nothing outside the network can reach the service, and that is a property of the ingress configuration rather than of any code here. See ADR-0007.

It cannot bootstrap the realm it authenticates against. keycloak bootstrap and keycloak sync create the client whose credential it presents, so they run first.

3. Keycloak CLI

A typer CLI (src/celine/policies/cli/) that manages Keycloak configuration. Each command owns one level of the realm and checks the levels below it, refusing with the command to run instead of writing them:

platform — platform.yaml, written by bootstrap;
clients — clients.yaml, written by sync;
organizations and users — written by sync-orgs, sync-users and the provisioning service.

Commands: - bootstrap — converge the platform level from platform.yaml (only the keys it declares; a deployment overlay may narrow supportedLocales and nothing else), brute force from CELINE_KEYCLOAK_BRUTE_FORCE_ENABLED, smtpServer from CELINE_KEYCLOAK_SMTP_*, the built-in account-console client's missing default client scopes; then create or refresh the celine-admin-cli service account with realm-management roles. It refuses a theme the server does not list. With CELINE_KEYCLOAK_REALM_ADMIN_USERNAME set it creates the operator realm admin once and keeps it in /admins. With the admin CLI client's own credentials it converges the platform and skips the client - sync — reconcile scopes, clients, audience mappers, the realm claim scopes and service-account administration rights in Keycloak to match clients.yaml. It refuses to grant admin_permissions on a realm where bootstrap has not turned them on - sync-users — create Keycloak users from a rec-registry REC definition YAML, and file them in the groups clients.yaml declares a service account may administer. --invite creates them with no password and invites each account it created in that run, under the provisioning service's email settings - sync-orgs — create Keycloak organizations from an owners.yaml - sync-orgs and sync-users refuse a realm without Organizations (bootstrap) or without the realm claim scopes (sync), in a dry run too - set-password — set a user's password; development realms only (ENV=dev) - seed-dev-users — create the development users (admin, manager, editor, viewer, from config/keycloak/dev-users.yaml) with their groups; development realms only, and a password is never reset - set-user-organization — assign a user to organizations and org-level groups - status — show current scopes, clients, and assignments

Authentication to Keycloak uses either admin user credentials (--admin-user) or a service account client (celine-admin-cli) whose secret is stored in .client.secrets.yaml after bootstrap. Both bootstrap and sync write that file through one merging writer, so a sync cannot delete the credential a bootstrap put there; it holds one realm at a time.

4. Rego Policies

Two policy files under policies/celine/:

scopes.rego — shared helpers for checking subject type (user vs service), scope membership, group membership, and admin detection. Supports multiple group naming conventions (service.resource.verb, mqtt:service:resource:verb, wildcards).
mqtt/acl.rego — MQTT topic ACL rules. Parses topics following the celine/{service}/{resource}/{...} convention and decides allow/deny based on:
Service admin scopes (e.g. digital-twin.admin)
User admin groups (admin, mqtt.admin, {service}.admin)
Fine-grained scopes/groups matching {service}.{resource}.{verb}

MQTT Authorization Flow

MQTT Client ──(JWT as password)──> Mosquitto
                                      │
                               mosquitto-go-auth
                                      │
                          ┌───────────┼───────────┐
                          │           │           │
                      /user       /acl      /superuser
                          │           │           │
                     JWT valid?   OPA eval    admin scope?
                          │           │           │
                        200/403    200/403     200/403

Client connects to Mosquitto with a JWT (obtained from Keycloak) as the MQTT password.
Mosquitto calls /user — the service validates the JWT signature, issuer, and expiry.
On publish/subscribe, Mosquitto calls /acl — the service builds a PolicyInput from the JWT claims (subject, scopes, groups) and the requested topic/action, then evaluates celine.mqtt.acl via regorus.
Optionally, /superuser is checked — grants bypass if the JWT carries mqtt.admin scope or admin group.

Keycloak Sync Flow

clients.yaml ─────────┐   celine's own services — a whole realm on its own
clients.ds-host.yaml ─┤   the grants celine adds to ds's clients   ┐ only where a
<ds>/clients.yaml ────┘   ds's own declaration of those clients    ┘ dataspace runs
          │
          └─ merge (--overlay, repeatable)
                 │
                 ├─ compute diff
                 │    scopes to create/update
                 │    clients to create/update
                 │    scope assignments
                 │    audience mappers
                 │
                 ├─ apply changes ──> Keycloak Admin API
                 │
                 └─ .client.secrets.yaml

The sync command:

Loads clients.yaml (scopes + clients with default_scopes and scopes_prefix), merged with every --overlay file into one declaration — a realm may be declared by more than one party, and syncing half of it silently narrows the clients it mentions
Fetches current state from Keycloak (existing scopes, clients, assignments)
Computes a diff (plan): scopes to create/update, clients to create/update, scope assignments to add/remove
Applies changes idempotently
Merges the client secrets it generated into .client.secrets.yaml, keeping the entries this run did not touch — celine-admin-cli among them, which is what the next run with no --admin-user authenticates with

The scopes_prefix field on each client declares scope ownership. The CLI uses this to automatically add audience mappers so that user JWTs issued through oauth2-proxy carry the correct audience for each service.

Topic Naming Convention

MQTT topics follow the pattern:

celine/{service}/{resource}/{...}

The ACL policy derives the required scope as {service}.{resource}.{verb} (where verb is read for subscribe/read, write for publish).

Examples: - celine/pipelines/runs/pipeline-123 → requires pipelines.runs.read (subscribe) or pipelines.runs.write (publish) - celine/digital-twin/events/pump/pump-001 → requires digital-twin.events.read or digital-twin.events.write

Service-level wildcards (celine/{service}/#) require service admin access.

Subject Types

Type	Identification	Authorization
User	JWT has groups	Group-based access (via `scopes.rego` helpers)
Service	JWT has scopes but no groups	Scope-based access
Anonymous	No valid JWT	Denied

Configuration

The MQTT auth service is configured via environment variables with the CELINE_ prefix (see MqttAuthSettings):

Variable	Default	Description
`CELINE_OIDC_*`	(from celine-sdk)	OIDC/JWT validation settings
`CELINE_POLICIES_DIR`	`./policies`	Path to Rego policy files
`CELINE_POLICIES_DATA_DIR`	`None`	Path to policy data JSON files
`CELINE_POLICIES_CACHE_ENABLED`	`true`	Enable decision caching
`CELINE_POLICIES_CACHE_TTL`	`300`	Cache TTL in seconds
`CELINE_POLICIES_CACHE_MAXSIZE`	`10000`	Max cache entries
`CELINE_MQTT_POLICY_PACKAGE`	`celine.mqtt.acl`	Rego package to evaluate
`CELINE_MQTT_SUPERUSER_SCOPE`	`mqtt.admin`	Scope for superuser access

The Keycloak CLI is configured via CELINE_KEYCLOAK_* environment variables (see KeycloakSettings):

Variable	Default	Description
`CELINE_KEYCLOAK_BASE_URL`	`http://keycloak.celine.localhost`	Keycloak URL
`CELINE_KEYCLOAK_REALM`	`celine`	Target realm
`CELINE_KEYCLOAK_ADMIN_USER`	—	Admin username (for bootstrap)
`CELINE_KEYCLOAK_ADMIN_PASSWORD`	—	Admin password (for bootstrap)
`CELINE_KEYCLOAK_ADMIN_CLIENT_ID`	`celine-admin-cli`	Service client ID
`CELINE_KEYCLOAK_ADMIN_CLIENT_SECRET`	—	Service client secret
`CELINE_KEYCLOAK_SECRETS_FILE`	`.client.secrets.yaml`	Auto-load secret from file