auth

name	auth
description	Epicenter auth packages: `@epicenter/auth` and the Svelte wrapper at `@epicenter/svelte/auth`, OAuth sessions, identity state, auth-owned fetch/WebSocket, and workspace lifecycle binding. Use when editing Epicenter auth clients, session state, hosted sign-in, or auth/workspace integration.
metadata	{"author":"epicenter","version":"6.0"}

Epicenter Auth

Upstream Grounding

When changes depend on Better Auth OAuth provider behavior, bearer token verification, cookie handling, token rotation, plugin shape, JWKS, or generated API shape, ask DeepWiki a narrow question against better-auth/better-auth before relying on memory. Use it to orient, then verify decisive details against local installed types, source, tests, or official docs before changing code.

Known Better Auth source landmarks:

packages/oauth-provider/src/oauth.ts
packages/oauth-provider/src/authorize.ts
packages/oauth-provider/src/token.ts
packages/oauth-provider/src/revoke.ts
packages/oauth-provider/src/client-resource.ts
packages/better-auth/src/plugins/jwt/index.ts   (ES256 signing + JWKS)

Better Auth remains the auth server and session engine. Epicenter extends it through plugins and options; it does not replace Better Auth's server-side session model.

Use this composition sentence when explaining the architecture:

Epicenter uses Better Auth for auth-server machinery, OAuth for the app/resource boundary, and AuthState{ownerId} for workspace boot.

That means Better Auth owns users, account cookies, login, consent, token issuing, revocation, JWKS, and metadata. Epicenter clients store PersistedAuth, not Better Auth sessions. /api/session is the adapter that verifies an OAuth access token, resolves the request to an ownerId, and returns ApiSessionResponse.

When the user asks whether this is idiomatic Better Auth, be precise:

It is not the shortest Better Auth browser-cookie path.
It is an idiomatic composition of Better Auth as the auth server beneath a cross-client OAuth runtime.

Do not suggest removing Better Auth unless the user has a concrete blocker that cannot be handled with configuration, a small adapter, or an upstream fix. Building OAuth by hand means owning PKCE validation, redirect URI validation, state and mix-up protections, trusted clients, token signing, refresh token rotation, revocation, JWKS, metadata, consent, account sessions, and security fixes forever.

Current Model

Epicenter app clients use one OAuth app auth factory:

const auth = createOAuthAppAuth({
	baseURL: EPICENTER_API_URL,
	clientId,
	launcher,
	persistedAuthStorage,
});

There is exactly one factory. The old split between createCookieAuth and createBearerAuth (and BearerSession / auth.bearerToken) is fully removed, not legacy-but-present. Do not reintroduce those names.

The public surface lives in one package plus a Svelte subpath:

• @epicenter/auth: framework-agnostic core. Owns the persisted auth cell, refresh, refresh-token revocation, /api/session verification, the network gate, authenticated fetch, and WebSocket opening. Also exports the Node machine-auth surface for CLI and daemons.
• @epicenter/svelte/auth: Svelte 5 wrapper (in the @epicenter/svelte package, which also owns createSession / SignedIn). Mirrors auth.state through createSubscriber so templates and $derived reads are reactive.
• createSession / SignedIn from @epicenter/svelte: workspace lifecycle binding over an AuthClient.

The API server composes Better Auth like this:

Hono app
  -> CORS
  -> per-request DB
  -> createAuth({ db, env, baseURL })
  -> singleCredential
  -> /auth/* Better Auth handler
  -> /api/session (mountSessionApp: cookie-or-bearer + ownership)
  -> protected resources (bearer + ownership)

createAuth() configures Better Auth with Drizzle (Postgres via Hyperdrive), Google sign-in (plus GitHub when its credentials are present), and exactly two plugins:

jwt({ jwks: { keyPairConfig: { alg: JWT_SIGNING_ALG } } }), // ES256
oauthProvider({
	loginPage: '/sign-in',
	consentPage: '/consent',
	requirePKCE: true,
	accessTokenExpiresIn: 600,
	cachedTrustedClients: trustedOAuthClientIds,
	validAudiences: [apiBaseURL],
	allowDynamicClientRegistration: false,
	scopes: [...EPICENTER_OAUTH_SCOPES],
})

There are no bearer, device-authorization, or custom-session plugins. Local email/password is disabled (emailAndPassword: { enabled: false }): enabling unverified local credentials reopens an account-linking takeover on better-auth 1.5.6 (no requireLocalEmailVerified gate). Only Google is a trusted linking provider; see the better-auth-security skill's Account Linking note.

Public Surface

Auth has one public client interface (copied verbatim from packages/auth/src/auth-contract.ts):

export type AuthState =
	| { status: 'signed-out' }
	| {
			status: 'signed-in';
			ownerId: OwnerId;
	  }
	| {
			status: 'reauth-required';
			ownerId: OwnerId;
	  };

export type AuthClient = {
	state: AuthState;
	baseURL: string;
	onStateChange(fn: (state: AuthState) => void): () => void;
	startSignIn(): Promise<Result<undefined, AuthError>>;
	signOut(): Promise<Result<undefined, AuthError>>;
	fetch(input: Request | string | URL, init?: RequestInit): Promise<Response>;
	openWebSocket(url: string | URL, protocols?: string[]): Promise<WebSocket>;
	[Symbol.dispose](): void;
};

AuthState arms carry ownerId directly. There is no nested identity object and no user field in state: profile (user/email) is fetched by surfaces that display it, not held in state. ownerId is present in signed-in and reauth-required because it belongs to local workspace operations: even when the OAuth grant needs reauth, the cached owner id picks the right local storage partition.

Read auth.state synchronously. Use auth.onStateChange(fn) for future changes only; it does not replay. Consumers that need bootstrap behavior must read auth.state once and then register the listener.

Do not expose raw tokens above auth storage and transport boundaries. UI, workspace binding, AI fetches, and sync consume capabilities: auth.fetch and auth.openWebSocket.

The Persisted Cell

PersistedAuth is the single durable auth record (copied verbatim from packages/auth/src/auth-types.ts):

export const OAuthTokenGrant = type({
	'+': 'delete',
	accessToken: 'string',
	refreshToken: 'string',
	accessTokenExpiresAt: 'number',
});

export type OAuthTokenGrant = typeof OAuthTokenGrant.infer;

export const PersistedAuth = type({
	'+': 'delete',
	grant: OAuthTokenGrant,
	userId: UserId,
	ownerId: OwnerId,
});

export type PersistedAuth = typeof PersistedAuth.infer;

export const ApiSessionResponse = type({
	'+': 'delete',
	user: AuthUser,
	ownerId: OwnerId,
});

export type ApiSessionResponse = typeof ApiSessionResponse.infer;

The grant is a nested object; identity is split out:

PersistedAuth
  grant: { accessToken, refreshToken, accessTokenExpiresAt }  -> online-only server access
  userId   -> stored explicitly so the shared daemon can read it
  ownerId  -> local storage partition selection

The grant lets the app call the server and is useless offline on its own. userId / ownerId remain useful offline: they select this user's local workspace data. userId is stored explicitly rather than synthesised from ownerId so the shared daemon can read it when ownerId === SHARED_OWNER_ID (in shared mode ownerId is the literal shared id and is structurally not a UserId). Profile data is intentionally absent; application surfaces fetch it when they display it.

The app can boot from a cached PersistedAuth without calling the network. Refresh failure must preserve the cached ownerId so local workspace data can remain available. The cached owner id selects the local storage partition; it does not decrypt anything.

Network Gate (local-first invariant)

The runtime tracks a networkAccess state per signed-in cell (internal to createOAuthAppAuth):

networkAccess: 'unverified' | 'verified' | 'paused'

bearerForNetwork is the gate. It NEVER attaches a bearer until /api/session verifies the current persisted auth in this runtime:

signed-out / paused        -> no bearer
refresh stale grant        -> if refresh fails, no bearer (offline = fail closed)
unverified -> call /api/session
  ok                       -> mark verified, attach bearer
  AuthRejected (401/403)   -> pauseNetworkAuth() -> reauth-required
  Unavailable (offline)    -> no bearer; local workspace boot can continue by ownerId

Fail closed offline: server access is refused until the current persisted auth has been verified by the API, but local workspace boot continues because the cached ownerId selects the right local partition. A different-ownerId /api/session response wipes the local cell (same-owner guard).

auth.fetch layers retry on top of the gate: verify-before-attach, credentials: 'omit', one forced-refresh retry on a 401, and pauseNetworkAuth() on a second 401.

Sign-In Flow

Apps ask auth to start hosted sign-in. startSignIn takes NO arguments:

await auth.startSignIn();

The launcher decides how the runtime completes OAuth and returns one of two shapes:

• 'launched': control moved to a redirect / deep-link callback. The browser redirect launcher navigates to the hosted /sign-in and usually does not resolve before the page unloads.
• 'completed' with { grant }: the launcher exchanged a token grant in process (extension, OOB CLI). The runtime then calls /api/session, resolves identity, and persists PersistedAuth.

The return value of startSignIn is not the "user is signed in" signal. Observe auth.state.status === 'signed-in' for completion.

PersistedAuthStorage Port

Storage is a small port (copied verbatim from packages/auth/src/persisted-auth-storage.ts):

export type PersistedAuthStorage = {
	initial: PersistedAuth | null;
	set(value: PersistedAuth | null): void | Promise<void>;
};

initial is read exactly once, synchronously, at construction to seed the state machine; it is never re-read. set is the only write path (no watch hook: cross-context sign-out propagates via the server, where the next bearer-bearing call hits a revoked token and reauth-requires organically).

Adapters:

• createWebStoragePersistedAuthStorage({ key, storage }): sync Web Storage (localStorage / sessionStorage). A corrupt record reads as signed-out instead of throwing; write failures propagate so an unpersistable credential fails its sign-in or refresh.
• loadPersistedAuthStorage({ read, write }): pre-load an async-backed store (extension chrome.storage.local, a file) into a synchronous port. Await it before constructing the client so initial stays synchronous.
• parsePersistedAuth / serializePersistedAuth: the shared decode/encode helpers (re-validate against the arktype on both sides).

CLI and Daemon (machine auth)

packages/auth/src/node/machine-auth.ts is the Node surface. One auth file per API target lives at <dataDir>/auth/<host>.json with mode 0o600 (: in the host replaced by _); machineAuthFilePath({ baseURL }) resolves it. Loading refuses a file whose permissions are wider than 0o600.

• loginWithOob(...): runs the OOB OAuth dance once, calls /api/session for the identity, persists PersistedAuth, and returns the email for CLI output. It deliberately BYPASSES createOAuthAppAuth: login is a one-shot human action, and routing it through the factory would double the round-trip count.
• createMachineAuthClient(...): the daemon boot entry point. Loads the cell and constructs a normal createOAuthAppAuth client over a file-backed storage port. Its launcher errors on startSignIn (a human must run epicenter auth login to refresh the cell); daemons never sign in interactively.
• status / logout: read the cell and reach the server through a regular client. status returns 'unverified' on network failure so the CLI can still print the cached identity.

Transport

Use auth.fetch for HTTP resources:

const response = await auth.fetch(`${EPICENTER_API_URL}/api/ai/chat`, {
	method: 'POST',
	body,
});

auth.fetch runs the network gate (verify-before-attach), sends credentials: 'omit' so OAuth tokens stay the resource credential, retries one 401 after a forced refresh, and pauses network auth on a second 401. Storage writes are awaited before a refreshed token is used.

Use auth.openWebSocket for sync:

const collaboration = openCollaboration(workspace.ydoc, {
	url: roomWsUrl({ baseURL, ownerId, guid: workspace.ydoc.guid, nodeId }),
	waitFor: idb.whenLoaded,
	openWebSocket: signedIn.openWebSocket,
	onReconnectSignal: signedIn.onReconnectSignal,
});

Browsers cannot attach Authorization headers to new WebSocket(), so auth carries the bearer token as a WebSocket subprotocol (BEARER_SUBPROTOCOL_PREFIX). The API's singleCredential middleware normalizes that subprotocol into Authorization and rejects requests that carry multiple credentials.

Stateless access tokens and revocation windows

The OAuth provider issues JWT access tokens that the resource server verifies statelessly against JWKS (no per-request introspection). That is fast, but it means a token cannot be revoked before it expires: signing out revokes the refresh token, not the already-issued access token. Three mitigations follow from that one invariant and only make sense together. Treat them as a unit.

stateless JWT access token  ->  cannot revoke before exp
  1. short access-token TTL          (accessTokenExpiresIn: 600 / 10 min)
  2. bound WebSocket connection lifetime + force re-auth on reconnect
  3. classify verify failures: 401 (bad token) vs 503 (JWKS unreachable)

1. Keep accessTokenExpiresIn short (10 minutes). The client refreshes transparently (refresh tokens rotate; the runtime refreshes on a skew window and on any 401), so the UX cost is ~nil and the post-revocation window stays small.

2. A route that authenticates only at the WebSocket upgrade MUST bound the connection lifetime, or a socket opened with a valid token outlives the token. The rooms Durable Object closes an over-age socket and the client reconnects through a fresh authenticated upgrade. Crucially, a per-frame check misses idle sockets (their only traffic is the auto-responded ping), so the bound also needs an alarm-driven sweep over getWebSockets().

3. Close codes and statuses carry meaning the client acts on:

   WS close 4401  -> permanent auth failure; client gives up
   WS close 4408/4503 -> transient; client reconnects with backoff
   HTTP 401 (InvalidToken)  -> discard and refresh the token
   HTTP 503 (ServerError)   -> retry; the token is fine, JWKS was unreachable
   

   Never flatten a JWKS-fetch failure into a 401, or a transient server fault makes clients discard and refresh a good token and pause network auth.

Workspace Binding

Workspace construction reads identity from createSession and gives lower layers callbacks for data they need at their own boundary. The build callback receives a SignedIn value (copied verbatim from packages/svelte-utils/src/session.svelte.ts):

export type SignedIn = {
	server: string;
	baseURL: string;
	ownerId: OwnerId;
	openWebSocket: AuthClient['openWebSocket'];
	onReconnectSignal: AuthClient['onStateChange'];
};

Use it against the real createSession:

import { createSession, type SignedIn } from '@epicenter/svelte/auth';

export const session = createSession({
	auth,
	build: (signedIn: SignedIn) => {
		const workspace = createWorkspace({
			id: workspaceId,
			tables,
			kv,
		});
		const idb = attachLocalStorage(workspace.ydoc, {
			server: signedIn.server,
			ownerId: signedIn.ownerId,
		});
		const collaboration = openCollaboration(workspace.ydoc, {
			url: roomWsUrl({
				baseURL: signedIn.baseURL,
				ownerId: signedIn.ownerId,
				guid: workspace.ydoc.guid,
				nodeId,
			}),
			waitFor: idb.whenLoaded,
			openWebSocket: signedIn.openWebSocket,
			onReconnectSignal: signedIn.onReconnectSignal,
		});
		return {
			workspace,
			[Symbol.dispose]() {
				collaboration[Symbol.dispose]();
				idb[Symbol.dispose]();
			},
		};
	},
});

server is the API host alone (local-storage partition names); baseURL is the full origin (roomWsUrl wants the scheme for the wss:// upgrade).

createSession owns workspace lifecycle. A sign-out disposes the payload. A reauth-required transition keeps the existing payload mounted (OAuth sessions publish a signed-out gap before a different owner mounts, so two consecutive identity-bearing states are always the same owner). session.current is the nullable payload; session.require() throws when signed-out.

Local workspace data must not be wiped just because network auth failed. Wiping Yjs or local storage is a separate destructive user action.

Server Routes and Deployment Seam

/api/session is mounted via mountSessionApp(app, { ownership }), which wires requireCookieOrBearerUser (the endpoint serves both browser apps and API clients) plus createRequireOwnership, then mounts the handler. The handler returns { user: { id, email }, ownerId }.

External-only protected routes (AI chat, rooms) use requireBearerUser, which skips the cookie path and always answers 401 with a standard OAuth WWW-Authenticate header. Both auth middlewares verify the bearer through verifyAccessToken from oauthProviderResourceClient:

audience = c.var.authBaseURL          (the API origin)
issuer   = <API origin> + /auth
jwksUrl  = <API origin> + /auth JWKS

A token-verification failure (expired, bad audience/issuer/signature) is a real 401 (OAuthError.InvalidToken); an unreachable JWKS is a retryable 503 (OAuthError.ServerError). Never flatten the latter into a 401.

The deployment seam lives in packages/server/src/ownership.ts:

export type OwnershipRule =
	| { kind: 'personal' }
	| { kind: 'shared'; admit: Admit };

export const personal = (): OwnershipRule => ({ kind: 'personal' });
export const shared = (opts: { admit: Admit }): OwnershipRule => ({
	kind: 'shared',
	admit: opts.admit,
});

resolveOwnerPartition(rule, c) is the single switch on rule.kind. Personal mode returns the user's id branded as OwnerId (ownerId === userId). Shared mode runs the admission predicate and returns the literal SHARED_OWNER_ID, or RequestGuardError.NotAdmitted (403) for rejected users. createRequireOwnership sets c.var.ownerId and, on routes with a :ownerId segment, rejects a URL mismatch with OwnerMismatch (403).

Note: the same-origin dashboard SPA (apps/api/ui) uses createSameOriginCookieAuth, not PKCE. Served same-origin by the API, it already holds a first-party Better Auth session cookie after Google sign-in, so minting a bearer (and an unused offline_access refresh token) via PKCE against its own origin would be redundant. The cookie client uses that cookie directly (credentials: 'include', no Authorization), reads /api/session once for ownerId, and is a plain AuthClient (no openWebSocket: a billing surface has no sync). It is the cookie-credential sibling of createOAuthAppAuth, not a mode flag on it.

Common Pitfalls

• Do not add auth.bearerToken or any token reader. Token reading leaks transport details back into app code.
• Do not reintroduce cookie-vs-bearer app factories. Better Auth still uses cookies for hosted sign-in pages, but app resources use OAuth access tokens through the one createOAuthAppAuth factory.
• Do not treat startSignIn() resolving as signed-in. State is the source of truth; startSignIn takes no args.
• Do not clear local workspace data on refresh failure. Move to reauth-required (the runtime pauses network auth) and keep ownerId available for local partition selection.
• Do not let accessTokenExpiresAt decide local identity state. It is a transport refresh hint only; the resource server is the source of truth for token validity.
• Do not send both cookies and bearer tokens to resource routes. singleCredential rejects ambiguity before Better Auth sees it.
• Do not hide persistence failures in storage adapters. If set cannot save the refreshed cell, the failure must propagate, not silently look saved.
• Do not import requireSignedIn, InferSignedIn, openFuji, encryptionKeys, EncryptionKeys, keyring, or Keyring. They do not exist in Epicenter workspace auth. Workspace binding goes through createSession / SignedIn.