Both login attributes are used for authentication.
Login.ENAME_APP_ID is DACS application ID. If the server authenticates with DACS, the application may be required to pass in a valid ApplicationId.
Login.ENAME_POSITION is DACS position. If the server is authenticating with DACS, the application might be required to pass in a valid position.
As @Lars-at-Addicticks suggested, you can find more information in the "RDM Usage Guide", section "Login Request Elements".