Next.js -> NestJS Bearer Token Handoff Sending the session access token without leaking it into URLs or logs
Course principle: a user ID becomes trusted only after the access token has been cryptographically verified by the backend.
The HTTP contract GET /auth/me HTTP/1.1 Host: 127.0.0.1:4000 Authorization: Bearer <SUPABASE_ACCESS_TOKEN>
The access token belongs in the standard Authorization header. It should not be placed in query strings, route parameters, analytics events, or logs.
Server-side Next.js helper // apps/web/src/lib/api/authenticated-fetch.ts import { createClient } from '@/lib/supabase/server'
export async function authenticatedApiFetch( path: string, init: RequestInit = {}, ) { const supabase = await createClient() const { data, error } = await supabase.auth.getSession()
if (error || !data.session?.access_token) { throw new Error('Authenticated session required') }
const headers = new Headers(init.headers) headers.set( 'Authorization', `Bearer ${data.session.access_token}`, )
return fetch( `${process.env.API_BASE_URL}${path}`, { ...init, headers, cache: 'no-store' }, ) }
Phase 17 taught the difference between trusting a session and merely reading cookie contents. This helper is used only after the server-side auth layer has established the current session.
Browser-side calls A browser Client Component can also obtain the current session access token from Supabase and call NestJS. That path is subject to CORS because the browser is crossing origins. const { data } = await supabase.auth.getSession()
await fetch('http://127.0.0.1:4000/auth/me', { headers: { Authorization: `Bearer ${data.session?.access_token}`, }, })
Do not do this /auth/me?token=eyJ...
console.log(accessToken)
localStorage.setItem('debug-token', accessToken)
Bearer tokens are credentials. Treat them like secrets during their lifetime.
Source note: verified against current Supabase Auth/getClaims/signing-key guidance and NestJS authentication/authorization docs. Full URLs and version notes are included in SOURCE_NOTES.txt.
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 to NestJS Bearer Token Handoff” 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 guard + verification service + current-user helper + protected /auth/me and task routes.. 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 to NestJS Bearer Token Handoff” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Extract and validate the bearer scheme in a guard with clear missing/malformed behavior.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Decoding JWT without signature verification
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.