openvibers/openvibe.games Commits

POST /auth/fedcm on both hosts swaps a FedCM assertion for a session (jwt-bearer grant, nonce pre-check); silent login skips the Network when the ovg_sso cookie already resolves

OP OpenVibers committed 18 Sept 2026 · 9be6a8e495 · 6 files, +381 −27





Changes
ddiff --git a/apps/server/dist-types/net/httpServer.d.ts.map b/apps/server/dist-types/net/httpServer.d.ts.map
iindex a1d3b9c..53a577d 100644
---- a/apps/server/dist-types/net/httpServer.d.ts.map
++++ b/apps/server/dist-types/net/httpServer.d.ts.map
@@@ -1 +1 @@
--{"version":3,"file":"httpServer.d.ts","sourceRoot":"","sources":["../../src/net/httpServer.ts"],"names":[],"mappings":"AAEA,OAAO,EAAsC,KAAK,MAAM,EAAuB,MAAM,WAAW,CAAA;AAEhG,OAAO,KAAK,EAAE,MAAM,EAAE,MAAM,kBAAkB,CAAA;AAC9C,OAAO,KAAK,EAAE,aAAa,EAAE,MAAM,6BAA6B,CAAA;AAmBhE,OAAO,KAAK,EAAE,SAAS,EAAE,MAAM,mBAAmB,CAAA;AAyBlD,MAAM,WAAW,UAAU;IACzB,8BAA8B;IAC9B,GAAG,EAAE,MAAM,GAAG,IAAI,CAAA;IAClB,gFAAgF;IAChF,cAAc,EAAE,MAAM,GAAG,IAAI,CAAA;CAC9B;AAED,qFAAqF;AACrF,MAAM,WAAW,WAAW;IAC1B,QAAQ,EAAE,MAAM,CAAA;IAChB,YAAY,EAAE,MAAM,CAAA;IACpB,kEAAkE;IAClE,OAAO,EAAE,MAAM,CAAA;IACf,wEAAwE;IACxE,OAAO,EAAE,MAAM,CAAA;IACf,uEAAuE;IACvE,OAAO,EAAE,MAAM,CAAA;CAChB;AAgBD,wBAAgB,gBAAgB,CAC9B,SAAS,EAAE,MAAM,GAAG,IAAI,EACxB,OAAO,EAAE,aAAa,EACtB,GAAG,EAAE,MAAM,EACX,OAAO,CAAC,EAAE,MAAM,EAChB,UAAU,CAAC,EAAE,UAAU,EACvB,UAAU,CAAC,EAAE,CAAC,IAAI,EAAE,SAAS,EAAE,QAAQ,EAAE,MAAM,KAAK,IAAI,EACxD,cAAc,CAAC,EAAE,CACf,KAAK,EAAE,MAAM,EACb,IAAI,EAAE,MAAM,GAAG,SAAS,KACrB,OAAO,CAAC;IAAE,IAAI,EAAE,MAAM,CAAC;IAAC,IAAI,EAAE,MAAM,CAAC;IAAC,UAAU,EAAE,OAAO,CAAA;CAAE,EAAE,CAAC,EACnE,KAAK,CAAC,EAAE,WAAW,GAAG,IAAI,GACzB,MAAM,CA6aR"}
\\ No newline at end of file
++{"version":3,"file":"httpServer.d.ts","sourceRoot":"","sources":["../../src/net/httpServer.ts"],"names":[],"mappings":"AAEA,OAAO,EAAsC,KAAK,MAAM,EAAuB,MAAM,WAAW,CAAA;AAEhG,OAAO,KAAK,EAAE,MAAM,EAAE,MAAM,kBAAkB,CAAA;AAC9C,OAAO,KAAK,EAAE,aAAa,EAAE,MAAM,6BAA6B,CAAA;AAsBhE,OAAO,KAAK,EAAE,SAAS,EAAE,MAAM,mBAAmB,CAAA;AAyBlD,MAAM,WAAW,UAAU;IACzB,8BAA8B;IAC9B,GAAG,EAAE,MAAM,GAAG,IAAI,CAAA;IAClB,gFAAgF;IAChF,cAAc,EAAE,MAAM,GAAG,IAAI,CAAA;CAC9B;AAED,qFAAqF;AACrF,MAAM,WAAW,WAAW;IAC1B,QAAQ,EAAE,MAAM,CAAA;IAChB,YAAY,EAAE,MAAM,CAAA;IACpB,kEAAkE;IAClE,OAAO,EAAE,MAAM,CAAA;IACf,wEAAwE;IACxE,OAAO,EAAE,MAAM,CAAA;IACf,uEAAuE;IACvE,OAAO,EAAE,MAAM,CAAA;CAChB;AA6CD,wBAAgB,gBAAgB,CAC9B,SAAS,EAAE,MAAM,GAAG,IAAI,EACxB,OAAO,EAAE,aAAa,EACtB,GAAG,EAAE,MAAM,EACX,OAAO,CAAC,EAAE,MAAM,EAChB,UAAU,CAAC,EAAE,UAAU,EACvB,UAAU,CAAC,EAAE,CAAC,IAAI,EAAE,SAAS,EAAE,QAAQ,EAAE,MAAM,KAAK,IAAI,EACxD,cAAc,CAAC,EAAE,CACf,KAAK,EAAE,MAAM,EACb,IAAI,EAAE,MAAM,GAAG,SAAS,KACrB,OAAO,CAAC;IAAE,IAAI,EAAE,MAAM,CAAC;IAAC,IAAI,EAAE,MAAM,CAAC;IAAC,UAAU,EAAE,OAAO,CAAA;CAAE,EAAE,CAAC,EACnE,KAAK,CAAC,EAAE,WAAW,GAAG,IAAI,GACzB,MAAM,CAshBR"}
\\ No newline at end of file
ddiff --git a/apps/server/dist-types/net/sso.d.ts b/apps/server/dist-types/net/sso.d.ts
iindex 79935c3..37a7141 100644
---- a/apps/server/dist-types/net/sso.d.ts
++++ b/apps/server/dist-types/net/sso.d.ts
@@@ -44,6 +44,46 @@ export declare function clearSessionCookie(): string;
  export declare function ssoHintCookie(value: 'account' | 'guest', secure: boolean): string;
  export declare function loginStateCookie(s: LoginState, secure: boolean): string;
  export declare function clearLoginStateCookie(): string;
++/**
++ * Decodes a JWT's payload WITHOUT checking its signature. Only for reading
++ * claims we cross-check locally (the FedCM nonce); never for trusting an
++ * identity.
++ */
++export declare function decodeJwtPayload(token: string): Record<string, unknown> | null;
++/** True when the assertion's `nonce` claim is exactly the nonce the page posted. */
++export declare function fedcmNonceMatches(token: string, nonce: string): boolean;
++export interface FedcmBody {
++    token: string;
++    nonce: string;
++}
++/** Max bytes a /auth/fedcm body may carry: an assertion JWT is a few KB at most. */
++export declare const MAX_FEDCM_BODY_BYTES: number;
++/**
++ * Parses and validates the JSON body of POST /auth/fedcm. Returns an error
++ * code (for a 400) instead of the body when it is malformed, incomplete or
++ * its nonce does not match the assertion's.
++ */
++export declare function parseFedcmBody(raw: string): {
++    body: FedcmBody;
++} | {
++    error: string;
++};
++/**
++ * Remembers, briefly, which session tokens openvibe.network last confirmed so
++ * the silent-login shortcut (`/auth/login?silent=1` with an ovg_sso cookie
++ * that already resolves) does not cost a Network lookup on every page. Only
++ * positive answers are kept: a miss just falls through to the normal
++ * prompt=none round trip, which is the right answer for it anyway.
++ */
++export declare class SessionCheckCache {
++    private readonly ttlMs;
++    private readonly maxEntries;
++    private readonly hits;
++    constructor(ttlMs?: number, maxEntries?: number);
++    has(token: string, now?: number): boolean;
++    remember(token: string, now?: number): void;
++    forget(token: string): void;
++}
  /**
   * The page the callback answers with: it mirrors the session into
   * localStorage (the game client reads it from there) before moving on, so a
ddiff --git a/apps/server/dist-types/net/sso.d.ts.map b/apps/server/dist-types/net/sso.d.ts.map
iindex 836ee22..532bca4 100644
---- a/apps/server/dist-types/net/sso.d.ts.map
++++ b/apps/server/dist-types/net/sso.d.ts.map
@@@ -1 +1 @@
--{"version":3,"file":"sso.d.ts","sourceRoot":"","sources":["../../src/net/sso.ts"],"names":[],"mappings":"AAAA;;;;;;;GAOG;AAEH,oEAAoE;AACpE,eAAO,MAAM,cAAc,YAAY,CAAA;AACvC;;;;GAIG;AACH,eAAO,MAAM,eAAe,gBAAgB,CAAA;AAC5C,+EAA+E;AAC/E,eAAO,MAAM,kBAAkB,cAAc,CAAA;AAc7C,wBAAgB,cAAc,CAAC,KAAK,EAAE,MAAM,GAAG,IAAI,GAAG,SAAS,GAAG,OAAO,CAExE;AAED,MAAM,WAAW,WAAW;IAC1B,6FAA6F;IAC7F,OAAO,EAAE,MAAM,CAAA;IACf,+CAA+C;IAC/C,IAAI,EAAE,MAAM,EAAE,CAAA;CACf;AAED;;;;GAIG;AACH,wBAAgB,QAAQ,CAAC,GAAG,EAAE,MAAM,GAAG,IAAI,GAAG,SAAS,EAAE,OAAO,EAAE,WAAW,GAAG,MAAM,GAAG,IAAI,CA0B5F;AAED,0GAA0G;AAC1G,wBAAgB,WAAW,CAAC,IAAI,EAAE,MAAM,GAAG,MAAM,CAKhD;AAED,wBAAgB,YAAY,CAAC,MAAM,EAAE,MAAM,GAAG,SAAS,GAAG,MAAM,CAAC,MAAM,EAAE,MAAM,CAAC,CAe/E;AAED,MAAM,WAAW,UAAU;IACzB,KAAK,EAAE,MAAM,CAAA;IACb,IAAI,EAAE,MAAM,GAAG,IAAI,CAAA;IACnB,MAAM,EAAE,OAAO,CAAA;CAChB;AAED,wBAAgB,gBAAgB,CAAC,CAAC,EAAE,UAAU,GAAG,MAAM,CAEtD;AAED,wBAAgB,gBAAgB,CAAC,GAAG,EAAE,MAAM,GAAG,SAAS,GAAG,UAAU,GAAG,IAAI,CAa3E;AAMD,wBAAgB,aAAa,CAAC,KAAK,EAAE,MAAM,EAAE,MAAM,EAAE,OAAO,GAAG,MAAM,CAEpE;AAED,wBAAgB,kBAAkB,IAAI,MAAM,CAE3C;AAED,wBAAgB,aAAa,CAAC,KAAK,EAAE,SAAS,GAAG,OAAO,EAAE,MAAM,EAAE,OAAO,GAAG,MAAM,CAEjF;AAED,wBAAgB,gBAAgB,CAAC,CAAC,EAAE,UAAU,EAAE,MAAM,EAAE,OAAO,GAAG,MAAM,CAEvE;AAED,wBAAgB,qBAAqB,IAAI,MAAM,CAE9C;AAOD;;;;GAIG;AACH,wBAAgB,kBAAkB,CAChC,KAAK,EAAE,MAAM,GAAG,IAAI,EACpB,IAAI,EAAE,SAAS,GAAG,OAAO,EACzB,IAAI,EAAE,MAAM,GACX,MAAM,CASR"}
\\ No newline at end of file
++{"version":3,"file":"sso.d.ts","sourceRoot":"","sources":["../../src/net/sso.ts"],"names":[],"mappings":"AAAA;;;;;;;GAOG;AAIH,oEAAoE;AACpE,eAAO,MAAM,cAAc,YAAY,CAAA;AACvC;;;;GAIG;AACH,eAAO,MAAM,eAAe,gBAAgB,CAAA;AAC5C,+EAA+E;AAC/E,eAAO,MAAM,kBAAkB,cAAc,CAAA;AAc7C,wBAAgB,cAAc,CAAC,KAAK,EAAE,MAAM,GAAG,IAAI,GAAG,SAAS,GAAG,OAAO,CAExE;AAED,MAAM,WAAW,WAAW;IAC1B,6FAA6F;IAC7F,OAAO,EAAE,MAAM,CAAA;IACf,+CAA+C;IAC/C,IAAI,EAAE,MAAM,EAAE,CAAA;CACf;AAED;;;;GAIG;AACH,wBAAgB,QAAQ,CAAC,GAAG,EAAE,MAAM,GAAG,IAAI,GAAG,SAAS,EAAE,OAAO,EAAE,WAAW,GAAG,MAAM,GAAG,IAAI,CA0B5F;AAED,0GAA0G;AAC1G,wBAAgB,WAAW,CAAC,IAAI,EAAE,MAAM,GAAG,MAAM,CAKhD;AAED,wBAAgB,YAAY,CAAC,MAAM,EAAE,MAAM,GAAG,SAAS,GAAG,MAAM,CAAC,MAAM,EAAE,MAAM,CAAC,CAe/E;AAED,MAAM,WAAW,UAAU;IACzB,KAAK,EAAE,MAAM,CAAA;IACb,IAAI,EAAE,MAAM,GAAG,IAAI,CAAA;IACnB,MAAM,EAAE,OAAO,CAAA;CAChB;AAED,wBAAgB,gBAAgB,CAAC,CAAC,EAAE,UAAU,GAAG,MAAM,CAEtD;AAED,wBAAgB,gBAAgB,CAAC,GAAG,EAAE,MAAM,GAAG,SAAS,GAAG,UAAU,GAAG,IAAI,CAa3E;AAMD,wBAAgB,aAAa,CAAC,KAAK,EAAE,MAAM,EAAE,MAAM,EAAE,OAAO,GAAG,MAAM,CAEpE;AAED,wBAAgB,kBAAkB,IAAI,MAAM,CAE3C;AAED,wBAAgB,aAAa,CAAC,KAAK,EAAE,SAAS,GAAG,OAAO,EAAE,MAAM,EAAE,OAAO,GAAG,MAAM,CAEjF;AAED,wBAAgB,gBAAgB,CAAC,CAAC,EAAE,UAAU,EAAE,MAAM,EAAE,OAAO,GAAG,MAAM,CAEvE;AAED,wBAAgB,qBAAqB,IAAI,MAAM,CAE9C;AAQD;;;;GAIG;AACH,wBAAgB,gBAAgB,CAAC,KAAK,EAAE,MAAM,GAAG,MAAM,CAAC,MAAM,EAAE,OAAO,CAAC,GAAG,IAAI,CAW9E;AAED,oFAAoF;AACpF,wBAAgB,iBAAiB,CAAC,KAAK,EAAE,MAAM,EAAE,KAAK,EAAE,MAAM,GAAG,OAAO,CAOvE;AAED,MAAM,WAAW,SAAS;IACxB,KAAK,EAAE,MAAM,CAAA;IACb,KAAK,EAAE,MAAM,CAAA;CACd;AAED,oFAAoF;AACpF,eAAO,MAAM,oBAAoB,QAAY,CAAA;AAE7C;;;;GAIG;AACH,wBAAgB,cAAc,CAAC,GAAG,EAAE,MAAM,GAAG;IAAE,IAAI,EAAE,SAAS,CAAA;CAAE,GAAG;IAAE,KAAK,EAAE,MAAM,CAAA;CAAE,CAcnF;AAID;;;;;;GAMG;AACH,qBAAa,iBAAiB;IAI1B,OAAO,CAAC,QAAQ,CAAC,KAAK;IACtB,OAAO,CAAC,QAAQ,CAAC,UAAU;IAJ7B,OAAO,CAAC,QAAQ,CAAC,IAAI,CAA4B;gBAG9B,KAAK,SAAS,EACd,UAAU,SAAO;IAGpC,GAAG,CAAC,KAAK,EAAE,MAAM,EAAE,GAAG,SAAa,GAAG,OAAO;IAU7C,QAAQ,CAAC,KAAK,EAAE,MAAM,EAAE,GAAG,SAAa,GAAG,IAAI;IAW/C,MAAM,CAAC,KAAK,EAAE,MAAM,GAAG,IAAI;CAG5B;AAOD;;;;GAIG;AACH,wBAAgB,kBAAkB,CAChC,KAAK,EAAE,MAAM,GAAG,IAAI,EACpB,IAAI,EAAE,SAAS,GAAG,OAAO,EACzB,IAAI,EAAE,MAAM,GACX,MAAM,CASR"}
\\ No newline at end of file
ddiff --git a/apps/server/src/net/httpServer.ts b/apps/server/src/net/httpServer.ts
iindex 59ffd73..986eaac 100644
---- a/apps/server/src/net/httpServer.ts
++++ b/apps/server/src/net/httpServer.ts
@@@ -7,13 +7,16 @@ import type { ServerMetrics } from '../observability/metrics.js'
  import { canEditMap, fetchNetworkAccount, resolveNetworkUser } from './networkAuth.js'
  import {
    LOGIN_STATE_COOKIE,
++  MAX_FEDCM_BODY_BYTES,
    SESSION_COOKIE,
++  SessionCheckCache,
    clearLoginStateCookie,
    clearSessionCookie,
    decodeLoginState,
    isSilentDenial,
    loginStateCookie,
    parseCookies,
++  parseFedcmBody,
    safeNext,
    sessionCookie,
    sessionHandoffHtml,
@@@ -80,6 +83,35 @@ async function editorAuthorized(auth: EditorAuth, token: string | undefined): Pr
    return auth.key !== null && token === auth.key
  }
  
++/** Reads a small request body as utf8, or null when it exceeds `limit`. */
++function readBody(req: IncomingMessage, limit: number): Promise<string | null> {
++  return new Promise((resolvePromise) => {
++    const chunks: Buffer[] = []
++    let size = 0
++    let tooBig = false
++    req.on('data', (c: Buffer) => {
++      size += c.length
++      if (size > limit) {
++        tooBig = true
++        req.destroy()
++      } else chunks.push(c)
++    })
++    req.on('end', () => resolvePromise(tooBig ? null : Buffer.concat(chunks).toString('utf8')))
++    req.on('close', () => resolvePromise(null))
++    req.on('error', () => resolvePromise(null))
++  })
++}
++
++/** The token endpoint's answer, for both the code and the jwt-bearer grant. */
++interface TokenResponse {
++  access_token?: string
++  refresh_token?: string
++  error_description?: string
++  error?: string
++  user?: { username?: string; [key: string]: unknown }
++  preferences?: unknown
++}
++
  export function createHttpServer(
    staticDir: string | null,
    metrics: ServerMetrics,
@@@ -94,6 +126,9 @@ export function createHttpServer(
    oauth?: OAuthConfig | null,
  ): Server {
    const root = staticDir ? resolve(staticDir) : null
++  // Sessions the Network confirmed recently: lets a silent login on a signed-in
++  // browser answer without the Network round trip. See /auth/login.
++  const knownSessions = new SessionCheckCache()
    return createServer((req: IncomingMessage, res: ServerResponse) => {
      const url = (req.url ?? '/').split('?')[0] ?? '/'
      // Host-based routing: play.openvibe.games serves the game at its root
@@@ -295,27 +330,59 @@ export function createHttpServer(
        }
        // The game IS the root on the play host; on the apex it lives at /play.
        const home = playHost ? '/' : '/play'
++      // Where a session token is resolved to an account (see networkAuth.ts).
++      const networkMeUrl =
++        editorAuth?.networkAuthUrl ?? (oauth ? `${oauth.baseUrl}/api/auth/me` : null)
  
        if (url === '/auth/login' && oauth && redirectBase) {
--        // Both callbacks are registered with the provider; using the host the
--        // player came from means the callback lands back on that same host.
          const silent = query.get('silent') === '1'
          const next = safeNext(query.get('next'), origins)
--        const state = randomBytes(16).toString('hex')
--        const params = new URLSearchParams({
--          client_id: oauth.clientId,
--          redirect_uri: `${redirectBase}/auth/callback`,
--          response_type: 'code',
--          scope: 'profile theme',
--          state,
--        })
--        if (silent) params.set('prompt', 'none')
--        res.writeHead(302, {
--          location: `${oauth.baseUrl}/oauth/authorize?${params.toString()}`,
--          'set-cookie': loginStateCookie({ state, next, silent }, secure),
--          'cache-control': 'no-store',
++        const startLogin = () => {
++          // Both callbacks are registered with the provider; using the host the
++          // player came from means the callback lands back on that same host.
++          const state = randomBytes(16).toString('hex')
++          const params = new URLSearchParams({
++            client_id: oauth.clientId,
++            redirect_uri: `${redirectBase}/auth/callback`,
++            response_type: 'code',
++            scope: 'profile theme',
++            state,
++          })
++          if (silent) params.set('prompt', 'none')
++          res.writeHead(302, {
++            location: `${oauth.baseUrl}/oauth/authorize?${params.toString()}`,
++            'set-cookie': loginStateCookie({ state, next, silent }, secure),
++            'cache-control': 'no-store',
++          })
++          res.end()
++        }
++        const existing = silent ? cookies[SESSION_COOKIE] : undefined
++        if (!existing) {
++          startLogin()
++          return
++        }
++        // Silent login on a browser that is already signed in here: the
++        // Network would only hand back the session we hold, so go straight
++        // to `next`. Confirmed either from the short-lived cache or by one
++        // /api/auth/me lookup (the same check /auth/me itself makes).
++        const shortcut = () => {
++          res.writeHead(302, {
++            location: next ?? home,
++            'set-cookie': clearLoginStateCookie(),
++            'cache-control': 'no-store',
++          })
++          res.end()
++        }
++        if (knownSessions.has(existing)) {
++          shortcut()
++          return
++        }
++        void fetchNetworkAccount(networkMeUrl, existing).then((user) => {
++          if (user) {
++            knownSessions.remember(existing)
++            shortcut()
++          } else startLogin()
          })
--        res.end()
          return
        }
        if (url === '/auth/callback' && oauth && redirectBase) {
@@@ -373,12 +440,7 @@ export function createHttpServer(
                  redirect_uri: `${redirectBase}/auth/callback`,
                }),
              })
--            const data = (await resp.json()) as {
--              access_token?: string
--              error_description?: string
--              error?: string
--              user?: { username?: string }
--            }
++            const data = (await resp.json()) as TokenResponse
              if (!data.access_token) {
                res.writeHead(400, {
                  'content-type': 'text/plain',
@@@ -387,6 +449,7 @@ export function createHttpServer(
                res.end(`sign-in failed: ${data.error_description ?? data.error ?? 'no token'}`)
                return
              }
++            knownSessions.remember(data.access_token)
              // Land where the login asked to (a same-site page or the next hop
              // of the Network's sign-in-everywhere chain), else at the game.
              const dest = next ?? home
@@@ -408,10 +471,86 @@ export function createHttpServer(
          })()
          return
        }
++      if (url === '/auth/fedcm' && oauth) {
++        // Browser-native FedCM sign-in: the shared navbar posts the assertion
++        // JWT openvibe.network issued through the browser's account chooser,
++        // plus the nonce it put in the FedCM request. Same-origin JSON only.
++        // Both hosts serve it, like /auth/login: the play host's navbar
++        // posts to its own origin.
++        const json = (status: number, body: unknown, setCookie?: string[]) => {
++          res.writeHead(status, {
++            'content-type': 'application/json',
++            'cache-control': 'no-store',
++            ...(setCookie ? { 'set-cookie': setCookie } : {}),
++          })
++          res.end(JSON.stringify(body))
++        }
++        if (req.method !== 'POST') {
++          res.writeHead(405, { allow: 'POST', 'content-type': 'application/json' })
++          res.end('{"error":"method_not_allowed"}')
++          return
++        }
++        const contentType = (req.headers['content-type'] ?? '').split(';')[0]?.trim().toLowerCase()
++        if (contentType !== 'application/json') {
++          json(400, { error: 'invalid_request', error_description: 'Expected application/json' })
++          return
++        }
++        void readBody(req, MAX_FEDCM_BODY_BYTES).then(async (raw) => {
++          if (raw === null) {
++            json(400, { error: 'invalid_request', error_description: 'Body missing or too large' })
++            return
++          }
++          const parsed = parseFedcmBody(raw)
++          if ('error' in parsed) {
++            json(400, { error: 'invalid_request', error_description: parsed.error })
++            return
++          }
++          try {
++            // Same endpoint and answer shape as the code exchange; the
++            // Network verifies the assertion's signature and audience.
++            const resp = await fetch(`${oauth.baseUrl}/oauth/token`, {
++              method: 'POST',
++              headers: { 'content-type': 'application/json' },
++              body: JSON.stringify({
++                grant_type: 'urn:ietf:params:oauth:grant-type:jwt-bearer',
++                assertion: parsed.body.token,
++                client_id: oauth.clientId,
++                client_secret: oauth.clientSecret,
++              }),
++            })
++            const data = (await resp.json().catch(() => ({}))) as TokenResponse
++            if (!data.access_token) {
++              log.warn('fedcm exchange rejected', { error: data.error ?? 'no_token' })
++              json(401, {
++                error: data.error ?? 'invalid_grant',
++                error_description: data.error_description ?? 'openvibe.network rejected the assertion',
++              })
++              return
++            }
++            knownSessions.remember(data.access_token)
++            const user =
++              data.user ?? (await fetchNetworkAccount(networkMeUrl, data.access_token)) ?? null
++            // Exactly the session the callback sets up: the ovg_sso cookie
++            // plus the year-long, JS-readable ov_sso_hint=account.
++            json(200, { ok: true, user }, [
++              sessionCookie(data.access_token, secure),
++              ssoHintCookie('account', secure),
++            ])
++          } catch (err) {
++            log.warn('fedcm exchange failed', { error: String(err) })
++            json(502, {
++              error: 'server_error',
++              error_description: 'openvibe.network is unreachable — try again shortly',
++            })
++          }
++        })
++        return
++      }
        if (url === '/auth/logout') {
          // Drops this site's session and marks the browser a guest for the
          // whole network; `next` lets the sign-out-everywhere chain continue.
          const dest = safeNext(query.get('next'), origins) ?? home
++        if (cookies[SESSION_COOKIE]) knownSessions.forget(cookies[SESSION_COOKIE])
          res.writeHead(200, {
            'content-type': 'text/html; charset=utf-8',
            'cache-control': 'no-store',
@@@ -429,9 +568,7 @@ export function createHttpServer(
          // ovg_sso cookie (or a bearer token), { user: null } otherwise.
          const bearer = /^Bearer\s+(.+)$/i.exec(req.headers.authorization ?? '')?.[1]
          const token = cookies[SESSION_COOKIE] || bearer
--        const authUrl =
--          editorAuth?.networkAuthUrl ?? (oauth ? `${oauth.baseUrl}/api/auth/me` : null)
--        void fetchNetworkAccount(authUrl, token).then((user) => {
++        void fetchNetworkAccount(networkMeUrl, token).then((user) => {
            res.writeHead(200, {
              'content-type': 'application/json',
              'cache-control': 'private, no-store',
ddiff --git a/apps/server/src/net/sso.test.ts b/apps/server/src/net/sso.test.ts
iindex 8b59795..32d0bff 100644
---- a/apps/server/src/net/sso.test.ts
++++ b/apps/server/src/net/sso.test.ts
@@@ -1,14 +1,24 @@
  import { describe, expect, it } from 'vitest'
  import {
++  SessionCheckCache,
++  decodeJwtPayload,
    decodeLoginState,
    encodeLoginState,
++  fedcmNonceMatches,
    isSilentDenial,
    parseCookies,
++  parseFedcmBody,
    safeNext,
    sessionHandoffHtml,
    withSsoNone,
  } from './sso.js'
  
++/** An unsigned-but-well-formed JWT carrying `claims` (the Network checks signatures, not us). */
++function fakeJwt(claims: unknown): string {
++  const b64 = (v: unknown) => Buffer.from(JSON.stringify(v)).toString('base64url')
++  return `${b64({ alg: 'RS256', typ: 'JWT' })}.${b64(claims)}.c2ln`
++}
++
  const origins = {
    network: 'https://openvibe.network',
    self: ['https://openvibe.games', 'https://play.openvibe.games'],
@@@ -59,6 +69,65 @@ describe('login state cookie', () => {
    })
  })
  
++describe('fedcm assertion', () => {
++  it('decodes a payload without trusting it', () => {
++    expect(decodeJwtPayload(fakeJwt({ sub: 7, nonce: 'n1' }))).toEqual({ sub: 7, nonce: 'n1' })
++    expect(decodeJwtPayload('not-a-jwt')).toBeNull()
++    expect(decodeJwtPayload('a.b.c')).toBeNull()
++    expect(decodeJwtPayload(fakeJwt([1, 2]))).toBeNull()
++  })
++  it('accepts only the nonce the assertion was minted for', () => {
++    const token = fakeJwt({ sub: 7, nonce: 'expected' })
++    expect(fedcmNonceMatches(token, 'expected')).toBe(true)
++    expect(fedcmNonceMatches(token, 'other')).toBe(false)
++    expect(fedcmNonceMatches(token, 'expecte')).toBe(false)
++    expect(fedcmNonceMatches(token, '')).toBe(false)
++    expect(fedcmNonceMatches(fakeJwt({ sub: 7 }), 'expected')).toBe(false)
++    expect(fedcmNonceMatches(fakeJwt({ nonce: 7 }), '7')).toBe(false)
++  })
++  it('parses the posted body and rejects mismatches before anything reaches the Network', () => {
++    const token = fakeJwt({ sub: 7, nonce: 'n1' })
++    expect(parseFedcmBody(JSON.stringify({ token, nonce: 'n1' }))).toEqual({
++      body: { token, nonce: 'n1' },
++    })
++    expect(parseFedcmBody(JSON.stringify({ token, nonce: 'n2' }))).toEqual({
++      error: 'nonce_mismatch',
++    })
++    expect(parseFedcmBody(JSON.stringify({ nonce: 'n1' }))).toEqual({
++      error: 'missing_token_or_nonce',
++    })
++    expect(parseFedcmBody(JSON.stringify({ token, nonce: 5 }))).toEqual({
++      error: 'missing_token_or_nonce',
++    })
++    expect(parseFedcmBody('{nope')).toEqual({ error: 'malformed_json' })
++    expect(parseFedcmBody('"str"')).toEqual({ error: 'malformed_json' })
++    expect(parseFedcmBody('null')).toEqual({ error: 'malformed_json' })
++  })
++})
++
++describe('session check cache (silent-login shortcut)', () => {
++  it('remembers a confirmed session only until its ttl', () => {
++    const cache = new SessionCheckCache(1000)
++    expect(cache.has('tok', 0)).toBe(false)
++    cache.remember('tok', 0)
++    expect(cache.has('tok', 999)).toBe(true)
++    expect(cache.has('tok', 1000)).toBe(false)
++    expect(cache.has('tok', 500)).toBe(false) // an expired entry is gone for good
++  })
++  it('forgets on logout and never grows past its cap', () => {
++    const cache = new SessionCheckCache(1000, 2)
++    cache.remember('a', 0)
++    cache.forget('a')
++    expect(cache.has('a', 1)).toBe(false)
++    cache.remember('a', 0)
++    cache.remember('b', 0)
++    cache.remember('c', 0)
++    expect(cache.has('a', 1)).toBe(false) // oldest evicted
++    expect(cache.has('b', 1)).toBe(true)
++    expect(cache.has('c', 1)).toBe(true)
++  })
++})
++
  describe('cookies + handoff', () => {
    it('parses a cookie header', () => {
      expect(parseCookies('a=1; ovg_sso=tok%20en; b')).toEqual({ a: '1', ovg_sso: 'tok en' })
ddiff --git a/apps/server/src/net/sso.ts b/apps/server/src/net/sso.ts
iindex b2654ff..b50f5cc 100644
---- a/apps/server/src/net/sso.ts
++++ b/apps/server/src/net/sso.ts
@@@ -7,6 +7,8 @@
   * Kept free of http.Server types so the rules are unit-testable on their own.
   */
  
++import { timingSafeEqual } from 'node:crypto'
++
  /** Name of the cookie holding the openvibe.network access token. */
  export const SESSION_COOKIE = 'ovg_sso'
  /**
@@@ -148,6 +150,112 @@ export function clearLoginStateCookie(): string {
    return `${LOGIN_STATE_COOKIE}=; Path=/auth; Max-Age=0; HttpOnly; SameSite=Lax`
  }
  
++// ── FedCM ──────────────────────────────────────────────────────────────
++// The shared navbar gets an assertion JWT from openvibe.network through the
++// browser's own account chooser and POSTs it to /auth/fedcm with the nonce
++// it put in the FedCM request. We only pre-check that nonce here; the
++// Network verifies the signature when it swaps the assertion for tokens.
++
++/**
++ * Decodes a JWT's payload WITHOUT checking its signature. Only for reading
++ * claims we cross-check locally (the FedCM nonce); never for trusting an
++ * identity.
++ */
++export function decodeJwtPayload(token: string): Record<string, unknown> | null {
++  const parts = token.split('.')
++  if (parts.length !== 3) return null
++  try {
++    const claims: unknown = JSON.parse(Buffer.from(parts[1] ?? '', 'base64url').toString('utf8'))
++    return claims && typeof claims === 'object' && !Array.isArray(claims)
++      ? (claims as Record<string, unknown>)
++      : null
++  } catch {
++    return null
++  }
++}
++
++/** True when the assertion's `nonce` claim is exactly the nonce the page posted. */
++export function fedcmNonceMatches(token: string, nonce: string): boolean {
++  if (!nonce || nonce.length > 256) return false
++  const claims = decodeJwtPayload(token)
++  if (!claims || typeof claims.nonce !== 'string') return false
++  const a = Buffer.from(claims.nonce)
++  const b = Buffer.from(nonce)
++  return a.length === b.length && timingSafeEqual(a, b)
++}
++
++export interface FedcmBody {
++  token: string
++  nonce: string
++}
++
++/** Max bytes a /auth/fedcm body may carry: an assertion JWT is a few KB at most. */
++export const MAX_FEDCM_BODY_BYTES = 16 * 1024
++
++/**
++ * Parses and validates the JSON body of POST /auth/fedcm. Returns an error
++ * code (for a 400) instead of the body when it is malformed, incomplete or
++ * its nonce does not match the assertion's.
++ */
++export function parseFedcmBody(raw: string): { body: FedcmBody } | { error: string } {
++  let parsed: unknown
++  try {
++    parsed = JSON.parse(raw)
++  } catch {
++    return { error: 'malformed_json' }
++  }
++  if (!parsed || typeof parsed !== 'object') return { error: 'malformed_json' }
++  const { token, nonce } = parsed as { token?: unknown; nonce?: unknown }
++  if (typeof token !== 'string' || !token || typeof nonce !== 'string' || !nonce) {
++    return { error: 'missing_token_or_nonce' }
++  }
++  if (!fedcmNonceMatches(token, nonce)) return { error: 'nonce_mismatch' }
++  return { body: { token, nonce } }
++}
++
++// ── Session check cache ─────────────────────────────────────────────────
++
++/**
++ * Remembers, briefly, which session tokens openvibe.network last confirmed so
++ * the silent-login shortcut (`/auth/login?silent=1` with an ovg_sso cookie
++ * that already resolves) does not cost a Network lookup on every page. Only
++ * positive answers are kept: a miss just falls through to the normal
++ * prompt=none round trip, which is the right answer for it anyway.
++ */
++export class SessionCheckCache {
++  private readonly hits = new Map<string, number>()
++
++  constructor(
++    private readonly ttlMs = 60_000,
++    private readonly maxEntries = 5000,
++  ) {}
++
++  has(token: string, now = Date.now()): boolean {
++    const until = this.hits.get(token)
++    if (until === undefined) return false
++    if (until <= now) {
++      this.hits.delete(token)
++      return false
++    }
++    return true
++  }
++
++  remember(token: string, now = Date.now()): void {
++    if (this.hits.size >= this.maxEntries) {
++      for (const [k, until] of this.hits) if (until <= now) this.hits.delete(k)
++      if (this.hits.size >= this.maxEntries) {
++        const oldest = this.hits.keys().next().value
++        if (oldest !== undefined) this.hits.delete(oldest)
++      }
++    }
++    this.hits.set(token, now + this.ttlMs)
++  }
++
++  forget(token: string): void {
++    this.hits.delete(token)
++  }
++}
++
  /** A JS string literal that cannot close the <script> it sits in. */
  function jsString(value: string): string {
    return JSON.stringify(value).replace(/</g, '\\u003c')