# Custom Token Authentication

With Firebase, you can also authenticate using a custom token that's been generated on your server. It works like this:

1. The user authenticates with your server
2. The server generates a new authentication token based on the user's unique ID
3. The token is passed back to the client and into the Chat SDK

**Generating the token**

To generate a token, you should follow the Firebase [custom authentication guide](https://firebase.google.com/docs/auth/admin/create-custom-tokens).

Firebase also has an Admin SDK for Node.js, Java, Python and Go which makes the process more straightforward. you can install it using this [guide](https://firebase.google.com/docs/admin/setup).

In PHP, an implementation may look like this:

```php
// Get your service account's email address and private key from the JSON key file
$service_account_email = "abc-123@a-b-c-123.iam.gserviceaccount.com";
$private_key = "-----BEGIN PRIVATE KEY-----...";

function create_custom_token($uid, $is_premium_account) {
  global $service_account_email, $private_key;

  $now_seconds = time();
  $payload = array(
    "iss" => $service_account_email,
    "sub" => $service_account_email,
    "aud" => "https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit",
    "iat" => $now_seconds,
    "exp" => $now_seconds+(60*60),  // Maximum expiration time is one hour
    "uid" => $uid,
    "claims" => array(
      "premium_account" => $is_premium_account
    )
  );
  return JWT::encode($payload, $private_key, "RS256");
}
```

The `id` should be the `id` your server uses to identify the user who is currently logged in. This token should be passed back to the app.

**Authenticating on the client**

{% tabs %}
{% tab title="Java" %}

```java
AccountDetails details = new AccountDetails.token("Your token");
ChatSDK.auth().authenticate(details).subscribe(...);
```

{% endtab %}

{% tab title="Objective-C" %}

```objectivec
BAccountDetails * details = [BAccountDetails token:@"Your token"];
[BChatSDK.auth authenticate: details].thenOnMain(...);
```

{% endtab %}
{% endtabs %}