feat(perf): measure the auth proxy per request (Server-Timing + proxy completed log) (#1922)

The proxy in front of every page, RSC, prefetch and /api request makes
several sequential network calls (getUser, session state, the
resolve_active_company RPC, MFA factor lookups) and nothing measured them,
while the route wrapper has logged authMs/companyMs/handlerMs per API call
for months. This is the first PR of the responsiveness plan (customer
report: "it takes time before all fields load when clicking around"): the
baseline every later change is measured against.

- lib/supabase/proxy-timing.ts: pure helpers (request classification from
  the app-router headers, route template that collapses ids and tokens,
  Server-Timing formatting, a timed() accumulator).
- lib/supabase/middleware.ts: updateSession wraps updateSessionInner, times
  each phase, sets Server-Timing on page/RSC/prefetch responses and
  X-Proxy-Timing on /api responses (withRouteContext owns Server-Timing
  there), and emits one "proxy completed" log line per request.
- scripts/perf/log-percentiles.ts: p50/p90/p99 per group over
  `vercel logs --json` output, for both "op completed" and
  "proxy completed"; scripts/perf/README.md documents the protocol and
  targets.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/supabase/__tests__/middleware.test.ts

@@ -72,6 +72,19 @@ vi.mock('@supabase/ssr', () => ({
   })),
 }))
 
+const logState = vi.hoisted(() => ({ info: vi.fn() }))
+
+vi.mock('@/lib/logger', () => {
+  const logger = {
+    info: (...args: unknown[]) => logState.info(...args),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn(),
+    child: () => logger,
+  }
+  return { createLogger: () => logger }
+})
+
 import { updateSession } from '../middleware'
 import {
   createSessionTimeoutState,
@@ -103,6 +116,7 @@ describe('updateSession redirect destinations', () => {
 
   beforeEach(() => {
     vi.clearAllMocks()
+    logState.info.mockClear()
     state.user = null
     state.sessionId = 'session-1'
     state.authError = null
@@ -535,6 +549,67 @@ describe('updateSession redirect destinations', () => {
 
   // ── MFA semantics that must not change ────────────────────────────────
 
+  describe('per-request timing header and log line', () => {
+    const TIMING_RE =
+      /^mw-auth;dur=\d+, mw-session;dur=\d+, mw-company;dur=\d+, mw-mfa;dur=\d+, mw-total;dur=\d+$/
+
+    function lastLog() {
+      expect(logState.info).toHaveBeenCalledTimes(1)
+      const [msg, ctx] = logState.info.mock.calls[0] as [string, Record<string, unknown>]
+      expect(msg).toBe('proxy completed')
+      return ctx
+    }
+
+    it('page responses carry Server-Timing and log kind=page with the route', async () => {
+      state.user = SIGNED_IN
+      const res = await run('/invoices')
+      expect(res.status).toBe(200)
+      expect(res.headers.get('server-timing')).toMatch(TIMING_RE)
+      expect(res.headers.get('x-proxy-timing')).toBeNull()
+      const ctx = lastLog()
+      expect(ctx.kind).toBe('page')
+      expect(ctx.route).toBe('/invoices')
+      expect(ctx.status).toBe(200)
+      expect(typeof ctx.totalMs).toBe('number')
+      expect(typeof ctx.authMs).toBe('number')
+      expect(typeof ctx.companyMs).toBe('number')
+    })
+
+    it('classifies prefetch and RSC requests from the app-router headers', async () => {
+      state.user = SIGNED_IN
+      await run('/invoices', { headers: { 'next-router-prefetch': '1', rsc: '1' } })
+      expect(lastLog().kind).toBe('prefetch')
+      logState.info.mockClear()
+      await run('/invoices', { headers: { rsc: '1' } })
+      expect(lastLog().kind).toBe('rsc')
+    })
+
+    it('/api responses use X-Proxy-Timing and leave Server-Timing to the route wrapper', async () => {
+      state.user = SIGNED_IN
+      const res = await run('/api/settings')
+      expect(res.headers.get('x-proxy-timing')).toMatch(TIMING_RE)
+      expect(res.headers.get('server-timing')).toBeNull()
+      expect(lastLog().kind).toBe('api')
+    })
+
+    it('redirect responses also carry the header and log their status', async () => {
+      const res = await run('/invoices')
+      expect(res.status).toBe(307)
+      expect(res.headers.get('server-timing')).toMatch(TIMING_RE)
+      expect(lastLog().status).toBe(307)
+    })
+
+    it('never logs a token-carrying path or a raw entity id', async () => {
+      const res = await run('/invite/9f8e7d6c5b4a3928171605f4e3d2c1b0')
+      expect(res.status).toBe(200)
+      expect(lastLog().route).toBe('/invite/*')
+      logState.info.mockClear()
+      state.user = SIGNED_IN
+      await run('/invoices/6f1c2a3e-1234-4bcd-9abc-0123456789ab')
+      expect(lastLog().route).toBe('/invoices/:id')
+    })
+  })
+
   describe('MFA-disabled and self-hosted paths are unchanged', () => {
     it('does not redirect when NEXT_PUBLIC_REQUIRE_MFA is unset', async () => {
       state.user = SIGNED_IN

lib/supabase/__tests__/proxy-timing.test.ts

@@ -0,0 +1,83 @@
+import { describe, it, expect } from 'vitest'
+import {
+  classifyProxyRequest,
+  createProxyTimings,
+  formatProxyServerTiming,
+  proxyRouteTemplate,
+  timed,
+} from '../proxy-timing'
+
+describe('classifyProxyRequest', () => {
+  it('treats /api paths as api regardless of headers', () => {
+    const headers = new Headers({ 'next-router-prefetch': '1', rsc: '1' })
+    expect(classifyProxyRequest('/api/settings', headers)).toBe('api')
+  })
+
+  it('recognises app-router prefetch and RSC requests by header', () => {
+    expect(
+      classifyProxyRequest('/invoices', new Headers({ 'Next-Router-Prefetch': '1', RSC: '1' })),
+    ).toBe('prefetch')
+    expect(classifyProxyRequest('/invoices', new Headers({ RSC: '1' }))).toBe('rsc')
+  })
+
+  it('falls back to page for a plain document request', () => {
+    expect(classifyProxyRequest('/invoices', new Headers())).toBe('page')
+  })
+})
+
+describe('proxyRouteTemplate', () => {
+  it('replaces UUID and numeric segments with placeholders', () => {
+    expect(proxyRouteTemplate('/invoices/6f1c2a3e-1234-4bcd-9abc-0123456789ab/edit')).toBe(
+      '/invoices/:id/edit',
+    )
+    expect(proxyRouteTemplate('/salary/runs/42')).toBe('/salary/runs/:n')
+  })
+
+  it('collapses token-carrying prefixes so secrets never reach the log', () => {
+    expect(proxyRouteTemplate('/invite/9f8e7d6c5b4a3928171605f4e3d2c1b0')).toBe('/invite/*')
+    expect(proxyRouteTemplate('/payslip/abc')).toBe('/payslip/*')
+    expect(proxyRouteTemplate('/auth/callback')).toBe('/auth/*')
+    expect(proxyRouteTemplate('/auth')).toBe('/auth/*')
+  })
+
+  it('masks long opaque segments outside the known prefixes', () => {
+    expect(proxyRouteTemplate('/e/sector/aVeryLongOpaqueSlugThatLooksLikeAToken')).toBe(
+      '/e/sector/:token',
+    )
+  })
+
+  it('keeps ordinary routes and the root untouched', () => {
+    expect(proxyRouteTemplate('/settings/company')).toBe('/settings/company')
+    expect(proxyRouteTemplate('/')).toBe('/')
+  })
+})
+
+describe('formatProxyServerTiming', () => {
+  it('emits one mw-* metric per phase plus the total', () => {
+    const timing = { authMs: 12, sessionMs: 3, companyMs: 40, mfaMs: 0 }
+    expect(formatProxyServerTiming(timing, 61)).toBe(
+      'mw-auth;dur=12, mw-session;dur=3, mw-company;dur=40, mw-mfa;dur=0, mw-total;dur=61',
+    )
+  })
+})
+
+describe('timed', () => {
+  it('returns the wrapped value and accumulates elapsed time on the key', async () => {
+    const timing = createProxyTimings()
+    const value = await timed(timing, 'sessionMs', async () => 'ok')
+    expect(value).toBe('ok')
+    await timed(timing, 'sessionMs', async () => undefined)
+    expect(timing.sessionMs).toBeGreaterThanOrEqual(0)
+    expect(timing.authMs).toBe(0)
+  })
+
+  it('still records time when the wrapped call throws', async () => {
+    const timing = createProxyTimings()
+    await expect(
+      timed(timing, 'authMs', async () => {
+        throw new Error('boom')
+      }),
+    ).rejects.toThrow('boom')
+    expect(timing.authMs).toBeGreaterThanOrEqual(0)
+  })
+})

lib/supabase/middleware.ts

@@ -1,5 +1,15 @@
 import { createServerClient } from '@supabase/ssr'
 import { NextResponse, type NextRequest } from 'next/server'
+import { createLogger } from '@/lib/logger'
+import {
+  PROXY_TIMING_HEADER,
+  classifyProxyRequest,
+  createProxyTimings,
+  formatProxyServerTiming,
+  proxyRouteTemplate,
+  timed,
+  type ProxyTimings,
+} from '@/lib/supabase/proxy-timing'
 import { shouldEnforceMfa } from '@/lib/auth/mfa'
 import { apiPathSkipsMfaGate } from '@/lib/auth/api-mfa-gate'
 import { DEFAULT_LOCALE, LOCALE_COOKIE, isLocale } from '@/i18n/config'
@@ -27,7 +37,43 @@ import {
   type SessionTimeoutReason,
 } from '@/lib/auth/session-timeout-shared'
 
+const log = createLogger('proxy')
+
+/**
+ * Auth proxy entry point. Wraps the real work so every response carries a
+ * per-phase timing header and emits one structured log line, mirroring what
+ * withRouteContext does for API routes: without it the proxy's sequential
+ * network calls (getUser, session state, company RPC, MFA lookups) were the
+ * one part of a request nobody could measure. Page/RSC/prefetch responses
+ * get `Server-Timing` (visible in the browser Timing tab); /api responses
+ * get `X-Proxy-Timing` so the route wrapper's own Server-Timing is left
+ * alone. Token-carrying paths are collapsed before logging.
+ */
 export async function updateSession(request: NextRequest) {
+  const start = Date.now()
+  const timing = createProxyTimings()
+  const response = await updateSessionInner(request, timing)
+  const totalMs = Date.now() - start
+  const pathname = request.nextUrl.pathname
+  const kind = classifyProxyRequest(pathname, request.headers)
+  response.headers.set(
+    kind === 'api' ? PROXY_TIMING_HEADER : 'Server-Timing',
+    formatProxyServerTiming(timing, totalMs),
+  )
+  log.info('proxy completed', {
+    kind,
+    route: proxyRouteTemplate(pathname),
+    status: response.status,
+    ...timing,
+    totalMs,
+  })
+  return response
+}
+
+async function updateSessionInner(
+  request: NextRequest,
+  timing: ProxyTimings,
+): Promise<NextResponse> {
   let supabaseResponse = NextResponse.next({
     request,
   })
@@ -62,7 +108,7 @@ export async function updateSession(request: NextRequest) {
   const {
     data: { user },
     error: authError,
-  } = await supabase.auth.getUser()
+  } = await timed(timing, 'authMs', () => supabase.auth.getUser())
 
   // Get the pathname
   const pathname = request.nextUrl.pathname
@@ -93,8 +139,12 @@ export async function updateSession(request: NextRequest) {
     !apiRequestSkipsSessionTimeout(pathname, hasAuthorizationHeader)
   ) {
     const encodedState = request.cookies.get(SESSION_TIMEOUT_COOKIE)?.value
-    const sessionId = await getSupabaseSessionId(supabase)
-    const verifiedState = await verifySessionTimeoutState(encodedState)
+    const sessionId = await timed(timing, 'sessionMs', () =>
+      getSupabaseSessionId(supabase),
+    )
+    const verifiedState = await timed(timing, 'sessionMs', () =>
+      verifySessionTimeoutState(encodedState),
+    )
 
     if (encodedState && !verifiedState) {
       await signOutTimedOutSession(supabase)
@@ -121,7 +171,9 @@ export async function updateSession(request: NextRequest) {
       const method = isSessionAuthMethod(hintedMethod)
         ? hintedMethod
         : 'password'
-      const autoLogout = await fetchAutoLogoutPreference(supabase, user.id)
+      const autoLogout = await timed(timing, 'sessionMs', () =>
+        fetchAutoLogoutPreference(supabase, user.id),
+      )
 
       // Unknown preference (failed read): mint nothing, so no fail-open
       // snapshot gets persisted; the next request retries the read.
@@ -184,8 +236,9 @@ export async function updateSession(request: NextRequest) {
       hasAuthorizationHeader,
     )
     if (!skipMfaGate && user && shouldEnforceMfa(user)) {
-      const { data: aal } =
-        await supabase.auth.mfa.getAuthenticatorAssuranceLevel()
+      const { data: aal } = await timed(timing, 'mfaMs', () =>
+        supabase.auth.mfa.getAuthenticatorAssuranceLevel(),
+      )
       if (aal?.nextLevel === 'aal2' && aal?.currentLevel === 'aal1') {
         return NextResponse.json({ error: 'MFA-verifiering krävs.' }, { status: 403 })
       }
@@ -310,11 +363,15 @@ export async function updateSession(request: NextRequest) {
     degraded: boolean
   } | null = null
   const resolveCompanyOnce = async () =>
-    (resolvedCompany ??= await resolveCompanyForMiddleware(supabase, user.id, request))
+    (resolvedCompany ??= await timed(timing, 'companyMs', () =>
+      resolveCompanyForMiddleware(supabase, user.id, request),
+    ))
 
   // MFA enforcement (application-side only, not RLS)
   if (shouldEnforceMfa(user)) {
-    const { data: aal } = await supabase.auth.mfa.getAuthenticatorAssuranceLevel()
+    const { data: aal } = await timed(timing, 'mfaMs', () =>
+      supabase.auth.mfa.getAuthenticatorAssuranceLevel(),
+    )
 
     // User has MFA enrolled but hasn't verified this session → redirect to verify
     if (aal?.nextLevel === 'aal2' && aal?.currentLevel === 'aal1') {
@@ -325,7 +382,9 @@ export async function updateSession(request: NextRequest) {
     // Skip for users with no companies (still setting up)
     const { companyId: companyIdForMfa } = await resolveCompanyOnce()
     if (companyIdForMfa) {
-      const { data: factors } = await supabase.auth.mfa.listFactors()
+      const { data: factors } = await timed(timing, 'mfaMs', () =>
+        supabase.auth.mfa.listFactors(),
+      )
       const hasVerifiedFactor = factors?.totp?.some(f => f.status === 'verified')
 
       if (!hasVerifiedFactor) {

lib/supabase/proxy-timing.ts

@@ -0,0 +1,115 @@
+/**
+ * Per-request timing for the auth proxy (lib/supabase/middleware.ts).
+ *
+ * The proxy runs in front of every page, RSC, prefetch and /api request and
+ * makes several sequential network calls (Supabase Auth, the active-company
+ * RPC, MFA factor lookups). Nothing measured that cost until now, while the
+ * route wrapper (lib/api/with-route-context.ts) has logged authMs/companyMs/
+ * handlerMs per API call for months. These helpers give the proxy the same
+ * Server-Timing header and one structured "proxy completed" log line per
+ * request so the fixed per-request cost can be read off Vercel logs and the
+ * browser Timing tab instead of guessed.
+ *
+ * Pure functions only: the middleware test suite mocks Supabase heavily, so
+ * classification and formatting live here where they can be unit-tested
+ * without that harness.
+ */
+
+export type ProxyRequestKind = 'api' | 'prefetch' | 'rsc' | 'page'
+
+export interface ProxyTimings {
+  /** supabase.auth.getUser(): a network round trip to Supabase Auth. */
+  authMs: number
+  /** Session-timeout state: getClaims + HMAC verify + auto_logout read. */
+  sessionMs: number
+  /** resolve_active_company RPC (or the query fallback) incl. write-back. */
+  companyMs: number
+  /** MFA assurance level + listFactors (the latter is a network call). */
+  mfaMs: number
+}
+
+export type ProxyTimingKey = keyof ProxyTimings
+
+/**
+ * Header used on /api responses. withRouteContext owns `Server-Timing` on
+ * API routes and only sets it when absent, so the proxy's numbers travel on
+ * a separate header there; on page/RSC responses nothing else sets
+ * Server-Timing and the proxy uses the standard header directly.
+ */
+export const PROXY_TIMING_HEADER = 'X-Proxy-Timing'
+
+export function createProxyTimings(): ProxyTimings {
+  return { authMs: 0, sessionMs: 0, companyMs: 0, mfaMs: 0 }
+}
+
+/** Run `fn` and add its wall time to `timing[key]` (accumulates on repeats). */
+export async function timed<T>(
+  timing: ProxyTimings,
+  key: ProxyTimingKey,
+  fn: () => Promise<T>,
+): Promise<T> {
+  const start = Date.now()
+  try {
+    return await fn()
+  } finally {
+    timing[key] += Date.now() - start
+  }
+}
+
+/**
+ * Which kind of request the proxy is fronting. Prefetch and RSC requests
+ * are recognised by the headers the Next.js app router sends
+ * (`Next-Router-Prefetch: 1`, `RSC: 1`); header names are case-insensitive
+ * on the Fetch `Headers` interface, so lower-case lookups are fine.
+ */
+export function classifyProxyRequest(
+  pathname: string,
+  headers: Headers,
+): ProxyRequestKind {
+  if (pathname.startsWith('/api')) return 'api'
+  if (headers.get('next-router-prefetch') === '1') return 'prefetch'
+  if (headers.get('rsc') === '1') return 'rsc'
+  return 'page'
+}
+
+const UUID_RE =
+  /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i
+const NUMERIC_RE = /^\d+$/
+/** Prefixes whose tail is a secret (invite tokens, payslip links, PKCE). */
+const TOKEN_PREFIXES = ['/invite', '/payslip', '/auth']
+
+/**
+ * Collapse a concrete pathname to a loggable route template: UUIDs become
+ * `:id`, numbers `:n`, long opaque segments `:token`, and paths under the
+ * token-carrying prefixes are cut to the prefix so a secret never lands in
+ * a log line.
+ */
+export function proxyRouteTemplate(pathname: string): string {
+  for (const prefix of TOKEN_PREFIXES) {
+    if (pathname === prefix || pathname.startsWith(`${prefix}/`)) {
+      return `${prefix}/*`
+    }
+  }
+  const segments = pathname.split('/').map((segment) => {
+    if (segment === '') return segment
+    if (UUID_RE.test(segment)) return ':id'
+    if (NUMERIC_RE.test(segment)) return ':n'
+    if (segment.length >= 24) return ':token'
+    return segment
+  })
+  return segments.join('/') || '/'
+}
+
+/** `Server-Timing` value: one `mw-*` metric per phase plus the total. */
+export function formatProxyServerTiming(
+  timing: ProxyTimings,
+  totalMs: number,
+): string {
+  return [
+    `mw-auth;dur=${timing.authMs}`,
+    `mw-session;dur=${timing.sessionMs}`,
+    `mw-company;dur=${timing.companyMs}`,
+    `mw-mfa;dur=${timing.mfaMs}`,
+    `mw-total;dur=${totalMs}`,
+  ].join(', ')
+}