> ## Documentation Index
> Fetch the complete documentation index at: https://docs.larksh.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Firebase Auth with Lark

> Use Firebase Authentication with your Lark database

If your users authenticate through Firebase Auth, Lark can validate those tokens directly. No code changes needed on the client.

## Setup

In your Lark project settings, set the **Firebase Auth Project ID** to your Firebase project ID. You can find this in the Firebase console under Project Settings.

This tells Lark how to validate the Firebase Auth tokens your clients send.

## How it works

1. Your client authenticates with Firebase Auth as usual.
2. The Firebase SDK sends the user's ID token when connecting to the database.
3. Lark validates the token's signature using Firebase's public keys.
4. Once validated, the `auth` object in your security rules contains the user's `uid` and claims from the Firebase token.

Your existing authentication flow works unchanged:

```javascript theme={null}
// Your existing Firebase Auth code works as-is
const user = firebase.auth().currentUser;
const token = await user.getIdToken();

// The Firebase SDK automatically sends this token to Lark
// when it connects to the database. You don't need to do
// anything extra.
```

<Note>Lark validates Firebase Auth tokens automatically using Firebase's public keys. Once validated, the user's identity is available in your security rules just like it would be in Firebase.</Note>

## Security rules

Once a Firebase Auth token is validated, the `auth` variable in your security rules works exactly as it does in Firebase:

```json theme={null}
{
  "rules": {
    "users": {
      "$uid": {
        ".read": "auth.uid === $uid",
        ".write": "auth.uid === $uid"
      }
    }
  }
}
```

Custom claims from Firebase Auth tokens are available under `auth.token`. For example, if you set an `admin` claim, you can check `auth.token.admin === true` in your rules.

## Using Lark's own auth instead

You can also use Lark's own token system (HS256 JWTs signed with your secret key) alongside or instead of Firebase Auth. This is useful if you're migrating away from Firebase Auth entirely or building new features that don't depend on it.

See [Authentication](/platform/authentication) for details on Lark's native auth system.