Mission Rebuild the capability of Phase 16 without following the exact code line-by-line. The goal is transfer: can you use the ideas when the variable names, UI, or route shape changes?
Required outcome Understand identity primitives before using a vendor: credentials, password hashing, sessions, JWTs, cookies, CSRF, expiration, renewal, and revocation.
Required artifact Authentication threat/flow diagram explaining what the browser stores, what servers verify, and what happens when credentials expire.
Constraints • Start from the previous phase checkpoint or a fresh branch. • Use the course architecture boundaries, but do not copy the reference implementation until after your first attempt. • Keep changes scoped to the capability. • Preserve validation, authorization, error handling, and observability expectations already earned in earlier phases. • Record any design decision where more than one implementation is reasonable.
Acceptance criteria • Can explain session vs token. • Can identify browser storage risks. • Can trace expiration/refresh. • Can separate identity from permission.
Independent build sequence 1. Draw password login without writing code and mark where plain-text password may exist temporarily. 2. Compare opaque sessions and JWT access tokens by state, revocation, and verification model. 3. Explain secure/httpOnly/sameSite cookie attributes and when browser JS should not read a token. 4. Trace token expiration and refresh as a state machine rather than a happy-path callback. 5. Separate authentication (who) from authorization (may do what) with concrete TaskFlow examples. 6. Write abuse cases: stolen token, CSRF, XSS, replay, brute force, user ID spoofing.
Self-review Compare your implementation to the reference only after the acceptance criteria pass. Differences are not automatically mistakes. For each difference, ask: does it preserve the same contract, security boundary, correctness, maintainability, and operational behavior? Keep the alternative when you can justify it with evidence.
Stretch challenge Change one assumption: more users, a second tenant, a slow network, an expired session, a concurrent mutation, a deployment restart, or a failed dependency. Predict whether your design still behaves correctly. If not, document the next architectural improvement rather than adding complexity blindly.
Phase exit Run the relevant checks, inspect Git diff, and write a three-sentence summary: what the system can do now, which boundary owns the new responsibility, and which failure you now know how to diagnose. Only then mark the phase complete.
Authentication answers who the request represents. Treating decoded or client-supplied identity as trusted is a security boundary failure.
Restate the goal of “Phase Synthesis & Independent Challenge” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: credentials/session → token → verification → trusted identity → protected operation. 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: Authentication threat/flow diagram explaining what the browser stores, what servers verify, and what happens when credentials expire.. 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 token = readBearerToken(request);
const claims = await verifier.verify(token);
request.user = {
id: claims.sub,
email: claims.email,
};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.
Inspect whether a token exists, whether it is expired, which issuer/audience signed it, and what the API verifier expects.
Trust only verified server claims; never repair identity by accepting a client-sent user id.
Without copying the final source, create a second small scenario that applies “Phase Synthesis & Independent Challenge” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Compare opaque sessions and JWT access tokens by state, revocation, and verification model.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Storing long-lived secrets in localStorage by default
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.