Private Channels and Realtime Authorization Volume 07 - Advanced Application Architecture
Authorization path Private workspace channel authorization
Policy allows SELECT on realtime.messages only when the JWT subject maps to a Workspace Membership.
This RLS protects the Realtime channel. NestJS still owns business authorization for writes.
Membership helper CREATE OR REPLACE FUNCTION public.can_receive_task_topic( requested_topic text ) RETURNS boolean LANGUAGE sql STABLE SECURITY DEFINER SET search_path = '' AS $$ SELECT EXISTS ( SELECT 1 FROM public."Membership" m JOIN public."User" u ON u.id = m."userId" WHERE u."authSubject" = (SELECT auth.uid())::text AND requested_topic = 'workspace:' || m."workspaceId"::text || ':tasks' ); $$;
Realtime SELECT policy CREATE POLICY "workspace members receive task broadcasts" ON realtime.messages FOR SELECT TO authenticated USING ( realtime.messages.extension = 'broadcast' AND public.can_receive_task_topic( (SELECT realtime.topic()) ) );
Function permissions The full reference migration revokes public execution and grants the helper only to the authenticated role.
Important architectural distinction This RLS authorizes the Realtime topic; NestJS still authorizes Task reads and writes.
For production, disable public channel access and join with private: true so the Realtime policy is enforced.
Authorization decides what an authenticated identity may do to a specific resource. UI hiding is never a substitute for server-side enforcement.
Restate the goal of “Private Channels and Realtime Authorization” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: trusted identity → requested action → resource scope → policy decision → allow/deny. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: Realtime task updates that merge into TanStack Query state with scoped subscriptions and reconnect behavior.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
const canEdit =
user.role === "ADMIN" ||
(user.role === "MEMBER" && task.ownerId === user.id);
if (!canEdit) throw new ForbiddenException();Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Trace verified identity, role, resource owner/workspace, and policy inputs separately.
Add server-side resource authorization; UI visibility is only experience, never enforcement.
Without copying the final source, create a second small scenario that applies “Private Channels and Realtime Authorization” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Test disconnect/reconnect and ensure a fresh server query repairs any missed events.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Realtime treated as database authority
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.