Adding project secret API key (PSAK) auth to an endpoint

What a PSAK is

A ProjectSecretAPIKey is a project-scoped, user-less service credential (posthog/models/project_secret_api_key.py). It behaves like a personal API key but survives users leaving the project, carries its own scopes, and authenticates as a synthetic user — not a real User row.

• Token format: phs_... (Bearer header only — no body fallback, unlike the legacy token).
• Scopes are project-wide within their resource type and deliberately ignore object-level access controls (per-resource RBAC).
• Do not confuse with TeamSecretTokenAuthentication — that validates the legacy per-team Team.secret_api_token (also phs_-prefixed) and is only for feature-flag local evaluation and similar pre-PSAK surfaces. It is pegged for migrating to PSAK at some point.

Keys are managed at POST /api/environments/:id/project_secret_api_keys (label + scopes; plaintext value returned once; roll action to rotate; max 50 per project; wildcard * scope not allowed).

Wiring a viewset action — the checklist

The machinery is shipped but nothing is wired to it yet — the first planned consumer is the endpoints (the product) run action. Four things, all required:

1. Whitelist the scope/action pair

PSAK-assignable scopes are a global allowlist in posthog/scopes.py:

PROJECT_SECRET_API_KEY_ALLOWED_API_SCOPE_ACTION: list[tuple[APIScopeObject, APIScopeActions]] = [("endpoint", "read")]

If your product isn't listed, key creation rejects the scope before auth is ever attempted. Add your (scope_object, action) tuple here first.

Add the same scope to PROJECT_SECRET_API_KEY_ALLOWED_API_SCOPE_ACTION in frontend/src/lib/scopes.tsx. The scope picker in project settings builds its checkboxes from that list, so a backend-only change leaves users with no way to grant the scope. posthog/test/test_scopes.py compares the two lists.

2. Add the authenticator and opt in actions

class MyViewSet(TeamAndOrgViewSetMixin, viewsets.ModelViewSet):
    scope_object = "endpoint"
    authentication_classes = [ProjectSecretAPIKeyAuthentication]  # extends, TeamAndOrgViewSetMixin keeps session/PAK auth
    psak_allowed_actions = ["run"]

psak_allowed_actions is default-deny: APIScopePermission rejects any PSAK request whose action isn't listed ("This action does not support project secret API key access"). List only the programmatic actions — never CRUD that should stay human-driven.

APIScopePermission also enforces team binding automatically: a PSAK only works against view.team == key.team, so PSAK auth only makes sense on project-scoped (/api/environments/:id/...) routes.

3. Use PSAK-aware throttles

PersonalApiKeyRateThrottle subclasses silently bypass PSAK requests (no personal key → no throttling). Use the PSAK-aware pair from posthog/rate_limit.py:

• PersonalOrProjectSecretApiKeyRateThrottle — per-key budget (keyed psak:{key_id}), also still throttles personal keys.
• ProjectSecretApiKeyTeamRateThrottle — per-team aggregate (keyed psak-team:{team_id}), caps total PSAK load regardless of how many keys a project mints. Stack it alongside the per-key throttle.

Subclass them to set product-specific scope/rate; remember each throttle keeps its own cache bucket per scope string.

4. Handle the synthetic user

request.user is a ProjectSecretAPIKeyUser (a SyntheticUser, posthog/synthetic_user.py), not a User:

• user.id is None — never use it as a foreign key. Use user.current_team_id.
• has_perm() always returns False — Django permission checks silently deny.

• Skip per-object access-control checks for it (PSAK scopes are project-wide by design):

  if is_authenticated_via_project_secret_api_key(request):
      return  # PSAK bypasses object-level RBAC deliberately

  Use isinstance(user, ProjectSecretAPIKeyUser) only where no request is in scope.

• report_user_action drops synthetic users — if you need analytics for PSAK-authenticated calls, capture explicitly with posthoganalytics.capture(distinct_id=user.distinct_id, ...) and include an auth_method property so both paths emit the same event shape.
• HogQL system tables: Database.create_for hides RBAC-scoped system tables the key's scopes don't cover (via readable_system_table_access_scopes()).

Helpers in posthog/permissions.py when you need to branch: is_authenticated_via_project_secret_api_key(request) and is_service_auth(request) (covers PSAK + legacy team token).

What you get for free

• Query tagging: the authenticator calls tag_authentication(access_method=AccessMethod.PROJECT_SECRET_API_KEY, api_key_mask=..., api_key_label=...), so ClickHouse query_log attribution works with no per-endpoint code. If you add a new authenticator, tag through tag_authentication (the single funnel in posthog/clickhouse/query_tagging.py) — not with ad-hoc tag_queries calls.
• last_used_at tracking: updated at most hourly via .update() (bypasses ModelActivityMixin so routine auth doesn't spam the activity log).
• Activity logging on key create/update/roll/delete.

Calling a PSAK-gated endpoint

curl -s https://us.posthog.com/api/environments/<project_id>/<your_action_path>/ \
  -H "Authorization: Bearer phs_<key>" \
  -H "Content-Type: application/json" \
  -d '{...}'

Testing

Mirror the PSAK sections of posthog/api/test/test_authentication.py, posthog/test/test_permissions.py, and posthog/test/test_rate_limit.py. Cover at minimum:

• allowed action with correct scope → 200
• action not in psak_allowed_actions → 403
• missing/wrong scope → 403
• key from another team's project → 403
• non-PSAK auth on the same action still works