Email auth

Tenant-scoped email and password sign-up and sign-in. Requires emailAndPassword.enabled: true in your Better Auth config.

Sign up

await authClient.signUpEmailTenant({
  tenantId: "<tenant-id>",
  email: "user@example.com",
  password: "secure-password",
  name: "Jane Doe",
  image: "https://example.com/avatar.png", // optional
  callbackURL: "/welcome", // optional, for email verification
  rememberMe: true, // optional, default true
});

Endpoint: POST /tenant/sign-up/email

The user is created with tenantId set and an email/password account linked to that tenant. If email verification is enabled, a verification email is sent using your configured sendVerificationEmail handler.

Sign in

await authClient.signInEmailTenant({
  tenantId: "<tenant-id>",
  email: "user@example.com",
  password: "secure-password",
  rememberMe: true, // optional
  callbackURL: "/dashboard", // optional
});

Endpoint: POST /tenant/sign-in/email

Sign-in validates credentials against the user record for that tenant only. The same email under a different tenant is a separate user with its own password.

Resolving the tenant

Pass tenantId in the request body, or use one of these alternatives:

• x-tenant-id header (or your custom tenantHeader)
• resolveTenantId callback — e.g. resolve from x-tenant-slug (see Configuration)

Multi-tenant email demo

1. Create tenants tenant-a and tenant-b
2. Sign up shared@demo.com on each with different passwords
3. Sign in to tenant-a only works with tenant-a's password, and likewise for tenant-b

Session

After sign-in or sign-up, the session includes tenantId. Use it to scope application data and authorization:

const { data: session } = await authClient.getSession();
console.log(session?.tenantId);

Related errors

Code	Meaning
USER_ALREADY_EXISTS	Email already registered for this tenant
INVALID_EMAIL_OR_PASSWORD	Wrong credentials for this tenant
EMAIL_NOT_VERIFIED	Email verification required
EMAIL_PASSWORD_NOT_ENABLED	Email/password auth disabled in config
TENANT_NOT_FOUND	Invalid or missing tenant id

See Error codes for the full list.