WMI里的“假冒和验证级别”到底是什么意思啊？

[xipx_osx]

比如下面那段代码
里面的【{impersonationLevel=impersonate,(Shutdown)}!】是所谓的“验证权限和假冒级别的”对吧？请问，何谓“验证权限和假冒级别”啊？这个有什么用呢？不写会怎样？

strComputer = "atl-dc-01"
Set objWMIService = GetObject("winmgmts:" _
& "{impersonationLevel=impersonate,(Shutdown)}!\\" & strComputer & "\root\cimv2")
Set colOperatingSystems = objWMIService.ExecQuery _
("Select * from Win32_OperatingSystem")
For Each objOperatingSystem in colOperatingSystems
ObjOperatingSystem.Reboot()
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