Authentication and Organizations

Session outcomes

Password sign-in can return a Session, a pending two-factor challenge, an unverified email, a Ban or a refusal. Treat those as distinct outcomes. session-outcome.ts and two-factor-outcome.ts provide the shared interpretation; hooks own navigation and error presentation.

The server registers two-factor, admin, organization, passkey, Expo and MCP OAuth plugins. Email verification policy comes from AUTH_SKIP_EMAIL_VERIFICATION; setup makes the intended policy explicit. Current server authorization reads the database, with cookie caching disabled.

Organizations and roles

Signup provisions a personal Organization. A User may be a Member of several Organizations; the Session selects one Active Organization. Todos and files belong to that Organization. Platform role admin grants global administration; Org roles owner, admin and member do not grant platform administration.

Membership must be checked at the operation, even if the UI already selected an Organization. An MCP token has no active selection and stays pinned to the User's personal Organization. See connecting agents.

Invitations

An invitation email is the app writing to a stranger on a signed-in User's behalf, so invite-member is treated as outbound mail, not as a form. Four controls apply, all in packages/auth (invitation-policy.ts):

Role. Only the Organization roles owner and admin hold invitation: create; a member holds no write permission. These are Better Auth's default roles, passed explicitly in the plugin configuration so a change is a visible diff.
Verified inviter. The inviter's email must be verified, regardless of AUTH_SKIP_EMAIL_VERIFICATION. With the default true, an account signs in unverified and can create Organizations, but its first invitation is refused with INVITER_EMAIL_NOT_VERIFIED until the address is confirmed; the web dialog and the mobile invite group show that state and offer to send the verification email. The choice is deliberate: skipping verification is a sign-in convenience for the account holder, not a licence to send mail in their name.
Daily caps. Rolling 24-hour counts on the invitation table: 20 per inviter across all Organizations (INVITATION_DAILY_LIMIT_REACHED) and 50 per Organization across all inviters (ORGANIZATION_INVITATION_DAILY_LIMIT_REACHED), both HTTP 429. Better Auth's invitationLimit caps pending invitations per Organization at 50 (INVITATION_LIMIT_REACHED). Constants live in INVITATION_POLICY.
Rate limit. /organization/invite-member has its own customRules entry, 10 requests per 10 minutes per client IP, next to the credential endpoints.

The checks run in beforeCreateInvitation, before the row is written and before any mail is sent, and again in a root hooks.before for the resend: true path, which re-sends an existing invitation without creating one. Counting runs on the handle Better Auth already holds (the auth.better-auth system scope, ADR-0009): one inviter's invitations span Organizations, so no tenant scope could see them all. The email itself never puts inviter text in the subject; see Email.

A refusal is a typed APIError; packages/errors maps each code to a message in every locale, and both clients show it through the shared mutation helper. Re-sending an existing invitation is not counted against the daily caps (the row already exists); the IP rule bounds it.

Web and native

Web auth hooks coordinate TanStack Query, forms and redirects. Mobile uses the Better Auth Expo client, secure credential storage and native passkey integration. Its route gate revalidates the Session and hides private content during a transition. Logout, expiry or an authoritative 401 clears private state. A 403 does not automatically sign out an otherwise valid Session.

Every web form with a password field sets method="post". The server-rendered ones (sign-in, sign-up, reset and change password) also keep submit disabled until useHydrated() is true, so a click before hydration never sends credentials in a GET URL.

Extend safely

Add auth behavior to the server factory and its tests, then expose the outcome through a hook. Keep email callbacks, membership checks and audit recording in their existing owners. Test revoked Sessions and Organization changes as well as successful login. Never treat an impersonated admin's original identity as permission to access /admin.