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建一个IdentityScope类，并引用相应的包

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace yokohama.util
{
    public class IdentityScope : IDisposable
       {  
        // obtains user token  
        [DllImport("advapi32.dll", SetLastError = true)]  
        static extern bool LogonUser(string pszUsername, string pszDomain, string pszPassword,  
            int dwLogonType, int dwLogonProvider, ref IntPtr phToken);  
  
        // closes open handes returned by LogonUser  
        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]  
        extern static bool CloseHandle(IntPtr handle);  
  
        [DllImport("Advapi32.DLL")]  
        static extern bool ImpersonateLoggedOnUser(IntPtr hToken);  
  
        [DllImport("Advapi32.DLL")]  
        static extern bool RevertToSelf();  
        const int LOGON32_PROVIDER_DEFAULT = 0;  
        const int LOGON32_LOGON_NEWCREDENTIALS = 9;//域控中的需要用:Interactive = 2  
        private bool disposed;  
        public IdentityScope(string sUsername, string sDomain, string sPassword)  
        {  
            // initialize tokens  
            IntPtr pExistingTokenHandle = new IntPtr(0);  
            IntPtr pDuplicateTokenHandle = new IntPtr(0);  
  
            try  
            {  
                // get handle to token  
                bool bImpersonated = LogonUser(sUsername, sDomain, sPassword,  
                    LOGON32_LOGON_NEWCREDENTIALS, LOGON32_PROVIDER_DEFAULT, ref pExistingTokenHandle);  
  
                if (true == bImpersonated)  
                {  
                    if (!ImpersonateLoggedOnUser(pExistingTokenHandle))  
                    {  
                        int nErrorCode = Marshal.GetLastWin32Error();  
                        throw new Exception("ImpersonateLoggedOnUser error;Code=" + nErrorCode);  
                    }  
                }  
                else  
                {  
                    int nErrorCode = Marshal.GetLastWin32Error();  
                    throw new Exception("LogonUser error;Code=" + nErrorCode);  
                }  
            }  
            finally  
            {  
                // close handle(s)  
                if (pExistingTokenHandle != IntPtr.Zero)  
                    CloseHandle(pExistingTokenHandle);  
                if (pDuplicateTokenHandle != IntPtr.Zero)  
                    CloseHandle(pDuplicateTokenHandle);  
            }  
        }  
  
        protected virtual void Dispose(bool disposing)  
        {  
            if (!disposed)  
            {  
                RevertToSelf();  
                disposed = true;  
            }  
        }  
  
        public void Dispose()  
        {  
            Dispose(true);  
        }  
    } 
}
using System;
using