> For the complete documentation index, see [llms.txt](https://docs.hackle.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.hackle.io/development-guide/sdk/user-identifier/server-user-identifier.md).

# 서버 사용자 식별자

서버에서는 사용자를 특정할 수 없기 때문에 **항상 사용자 지정 식별자를 파라미터로 전달**해야 합니다.

```java
// 테스트 그룹 분배
long experimentKey = 42L;
User user = User.builder().userId("ae2182e0");
Variation variation = hackleClient.variation(experimentKey, user);

// 사용자 이벤트 전송
hackleClient.track("purchase", user);
```

```python
# 테스트 그룹 분배
uesr = Hackle.user(user_id='ae2182e0')
variation = hackle_client.variation(experiment_key=42, user=user)

# 사용자 이벤트 전송
event = Hackle.event(key='purchase')
hackle_client.track(event=event, user=user)
```

```javascript
// 테스트 그룹 분배
const experimentKey = 42;
const user = { userId: "ae2182e0" };
hackleClient.variation(experimentKey, user);

// 사용자 이벤트 전송
hackleClient.track("purchase", user);
```

```php
// 테스트 그룹 분배
$experimentKey = 42;
$userId = 'ae2182e0'
$user = \Hackle\Common\HackleUser::builder()->userId($userId)->build();
$variation = $hackleClient->variation($experimentKey, $user);

// 사용자 이벤트 전송
$hackleClient->track('purchase', $user);
```

```ruby
# 테스트 그룹 분배
user = Hackle.user(user_id: 'ae2182e0')
variation = hackle_client.variation(experiment_key: 42, user: user)

# 사용자 이벤트 전송
event = Hackle.event(key: 'purchase')
hackle_client.track(event: event, user: user)
```

## 클라이언트, 서버 간 식별자 맞추기

클라이언트, 서버 SDK 를 동시에 사용하는 경우 각 환경에서 동일한 유저에 대해서 동일한 식별자로 맞추어 하여 사용할 수 있습니다.

이러한 경우에는 클라이언트, 서버간 API 통신시에 아래와 같이 HTTP 헤더를 통해서 식별자를 전달하는 방식을 권장드립니다.

```http
X-DEVICE-ID: a3017217-3d46-4d7e-8d88-a0a905709fe4
```


---

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