Datasnap 服务端 （Server）Session 管理： http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Server_Side_Session_Management
获取当前线程的会话（Session）——Getting the Current Thread‘s Session
From a server method, for example, you can obtain the current thread‘s session. This may provide you with useful information relating to the user issuing the current request. To do so, use the following code:
Session := TDSSessionManager.GetThreadSession;
通过 Session 可以获取 发出请求的 UserName 。