> For the complete documentation index, see [llms.txt](https://docs.baas.sh/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.baas.sh/baas-sdk/authentication/passkeys.md).

# Passkeys

Sign up new users and sign in returning ones with a passkey. The browser handles the rest in a single prompt.

## Sign up

For a brand-new user, create a passkey and sign them in:

```ts
const session = await baas.auth.signUpWithPasskey();
//  → { address: '0x…', accessToken: 'eyJ…', expiresAt: 1735689600 }
```

The browser asks the user to create a passkey, saved to iCloud Keychain, Google Password Manager, or another sync provider. On success, BaaS creates a fresh account and returns the session.

## Sign in

For a returning user, use their existing passkey:

```ts
const session = await baas.auth.signInWithPasskey();
```

If a valid session already exists, both methods return it immediately without showing a dialog.

{% hint style="info" %}
**Passkeys are scoped to your domain.** A passkey created on `app.example.com` is different from one on `example.com`. This is standard WebAuthn behaviour, not a bug. The same user on two domains has two distinct passkeys.
{% endhint %}

{% hint style="warning" %}
**Prefer synced passkeys.** The wallet address is derived from the passkey, so access to the account depends on it. On modern platforms, passkeys are usually **synced** (iCloud Keychain, Google Password Manager, 1Password, Bitwarden…) and survive a device change. A passkey that's bound to a single device, with no sync, is lost if that device is lost.

The SDK can't force the sync mode (the OS / authenticator decides), so encourage your users to keep their passkey manager's sync enabled.
{% endhint %}

## Next

* [External wallet](/baas-sdk/authentication/external-wallet.md) — let users sign in with MetaMask, Rainbow, or any EIP-1193 wallet.
* [Sessions](/baas-sdk/authentication/sessions.md) — read the session, listen for changes, and sign out.
* [Troubleshooting](/baas-sdk/troubleshooting.md) — common pitfalls, including the sign up vs sign in mistake.


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