Next.js 16 Proxy, Session Refresh & getClaims Keep SSR cookies synchronized and verify identity at the request boundary
Phase 17 - Supabase Authentication Volume 05 - Authentication & Security
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getClaims
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Phase 17 implements cookie-based Supabase Auth in Next.js. NestJS token verification remains Phase 18.
Next.js 16 uses Proxy for the request boundary Next.js renamed Middleware to Proxy in version 16. Supabase relies on this request boundary because Server Components cannot reliably write refreshed auth cookies themselves.
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proxy.ts runs
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createServerClient reads cookies
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getClaims verifies/refreshes access token
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request cookies updated
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response Set-Cookie updated
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Proxy keeps browser and server session state synchronized.
Why getClaims belongs here Current Supabase guidance says to use getClaims when protecting pages and user data. It verifies the access token signature against the project JWKS when asymmetric signing keys are used, and it refreshes a session that is near expiry.
getSession reads session storage but does not itself revalidate the stored user identity. Use getClaims for verified identity, or getUser when a fresh Auth-server user record is required.
Public vs protected paths TaskFlow protects /account and /tasks in this phase. /login and /auth/* remain public so users can establish or repair authentication. Phase 19 will add authorization beyond mere signed-in status.
function isProtectedPath(pathname: string) { return pathname.startsWith('/account') || pathname.startsWith('/tasks') }
const { data, error } = await supabase.auth.getClaims()
const authenticated = !error && Boolean(data?.claims)if (isProtectedPath(request.nextUrl.pathname) && !authenticated) { // redirect to /login }
Authentication answers who the request represents. Treating decoded or client-supplied identity as trusted is a security boundary failure.
Restate the goal of “Next.js 16 Proxy Session Refresh and getClaims” 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: 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.
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 “Next.js 16 Proxy Session Refresh and getClaims” 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.Stale UI after session changes
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.