Session when login using Java Engine API

Hi, im new Bonita, currenly i build Web Spring use Bonita Engine API community version.
The problem is a Session when i code login and logout. That mean If user1 login and perform start process, execute...etc, it work as well. But if when user2 login(user1 before login), the session will be replate by the last user(user2) and now user1 with any request will be use session of user2.
The problem same with logout when i can't specialize who will logout cause it just remove session not sessionId so it will record the last session who login last time.
Code login:

private static APISession session = null;
public String login(String user1, String pass){
        LoginAPI loginAPI = TenantAPIAccessor.getLoginAPI();
        session = loginAPI.login(user1, pass);
}

Code logout:

loginAPI.logout(session)

Any idea will be helpful, thanks