Security Boundaries & NestJS Handoff Define exactly what Phase 17 protects and what remains untrusted until Phase 18
Phase 17 - Supabase Authentication Volume 05 - Authentication & Security
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Phase 17 implements cookie-based Supabase Auth in Next.js. NestJS token verification remains Phase 18.
Phase 17 stops at the web-session boundary The user can now authenticate to Supabase and maintain a Next.js SSR session. The NestJS API is not protected yet. Keeping this boundary explicit prevents a dangerous illusion that a protected page automatically means a protected backend.
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Authentication is built layer by layer instead of trusting the browser.
What may be browser-visible Value Browser-visible?
Access token Credential - browser/session system may possess it; never log it
Refresh token Highly sensitive session credential; never log/expose intentionally
Do not use the database Auth schema as application authorization logic Supabase Auth maintains identity information in its auth schema. TaskFlow still has its own domain User, Membership, Workspace, Project, and Task records. Phase 19 will establish the explicit link from verified auth subject to application authorization data.
Supabase RLS is crucial when browser clients call Supabase Data APIs directly. TaskFlow business data currently flows through NestJS + Prisma instead. We will not introduce duplicate authorization systems without a concrete reason.
Security work starts with trust boundaries and abuse cases. A feature is incomplete until unauthorized and malformed paths are deliberately exercised.
Restate the goal of “Security Boundaries and NestJS Handoff” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: asset → trust boundary → attacker input → control → verified denial/allow. 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: Working TaskFlow authentication UI/session integration whose server-side checks are explicit and ready to hand tokens to NestJS.. 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.
Threat: authenticated User B changes the URL to User A's task id.
Expected control: API loads the resource scope and denies the action.
Evidence: 403 response + unchanged database row + security-safe log.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.
Return to the nearest observable boundary: input, network, process log, database, or rendered UI. Compare actual evidence with the predicted path.
Change one variable at a time and reproduce the original failure after the fix; otherwise you have correlation, not diagnosis.
Without copying the final source, create a second small scenario that applies “Security Boundaries and NestJS Handoff” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Render authenticated state on the server rather than trusting only client state.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Relying only on client-side route hiding
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.