通过LogonUser API，先切换登入账户，再设置文件的ACL

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.AccessControl;
using System.IO;
using System.Diagnostics;
using System.Security.Principal;
using System.Runtime.InteropServices;

namespace ConsoleApplication4
{
    internal class NativeMethods
    {
        // Methods
        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        internal static extern bool CloseHandle(IntPtr handle);
        [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        internal static extern bool DuplicateToken(IntPtr ExistingTokenHandle, int SECURITY_IMPERSONATION_LEVEL, ref IntPtr DuplicateTokenHandle);
        [DllImport("advapi32.dll", SetLastError = true)]
        internal static extern bool LogonUser(string lpszUsername, string lpszDomain, string lpszPassword, int dwLogonType, int dwLogonProvider, ref IntPtr phToken);
    }

    class Program
    {
        static void Main(string[] args)
        {
            string filePath = "ClientFile_0.txt";
            string userAccount = string.Format(@"{0}\{1}", Environment.UserDomainName, Environment.UserName);

            ImpersonateUser(Environment.GetEnvironmentVariable("COMPUTERNAME"), "Co9999CMLUser_0", "password(123");

            File.WriteAllText(filePath, string.Format("{0}", "Hello World ආයූෝබවන්"));
            FileSecurity fileSecurity = new FileSecurity();
            AddFileSecurity(filePath, userAccount,
                FileSystemRights.Read, AccessControlType.Deny);
            //RemoveFileSecurity(filePath, userAccount, FileSystemRights.Read, AccessControlType.Deny);
            //File.Delete(filePath);
            OutputFileAccess(filePath);

            //create windows user account
            //CreateUserAccount(Environment.GetEnvironmentVariable("COMPUTERNAME"), "Co9999CMLUser_0", "password(123");

            Console.WriteLine("Done!");
            Console.ReadLine();
        }

        private static bool LogonUser(string MachineName, string UserName, string Password, ref IntPtr tokenHandle)
        {
            tokenHandle = new IntPtr(0);
            tokenHandle = IntPtr.Zero;
            bool flag = NativeMethods.LogonUser(UserName, MachineName, Password, 2, 0, ref tokenHandle);
            if (!flag)
            {
                int num = Marshal.GetLastWin32Error();
                Console.WriteLine(" Failed with error code : {0}", num);
                //Console.WriteLine("\nError: [{0}] {1}\n", num, GetErrorMessage(num));
            }
            return flag;
        }

        public static WindowsImpersonationContext ImpersonateUser(string MachineName, string UserName, string Password)
        {
            IntPtr tokenHandle = new IntPtr(0);
            IntPtr duplicateTokenHandle = new IntPtr(0);
            if (!LogonUser(MachineName, UserName, Password, ref tokenHandle))
            {
                Console.WriteLine(MachineName);
                Console.WriteLine("Info_3047gs! CommonImpersonationUtilities::ImpersonateUser cannot test with local user");
                return null;
            }
            if (!NativeMethods.DuplicateToken(tokenHandle, 2, ref duplicateTokenHandle))
            {
                Console.WriteLine("Err_23efad! CommonImpersonationUtilities::ImpersonateUser cannot get token for the local user");
                NativeMethods.CloseHandle(tokenHandle);
                return null;
            }
            WindowsIdentity identity = new WindowsIdentity(duplicateTokenHandle);
            return identity.Impersonate();
        }

        public static void OutputFileAccess(string filePath)
        {
            FileSecurity fileSecurity = File.GetAccessControl(filePath);

            foreach (AuthorizationRule rule in fileSecurity.GetAccessRules(true, true, typeof(NTAccount)))
            {
                var fileRule = rule as FileSystemAccessRule;
                Console.WriteLine("Access type: {0}", fileRule.AccessControlType);
                Console.WriteLine("Rights: {0}", fileRule.FileSystemRights);
                Console.WriteLine("Identity: {0}",
                fileRule.IdentityReference.Value);
                Console.WriteLine();
            }
        }

        public static void AddFileSecurity(string fileName, string account, FileSystemRights rights, AccessControlType controlType)
        {
            // Get a FileSecurity object that represents the 
            // current security settings.
            FileSecurity fSecurity = File.GetAccessControl(fileName);

            // Add the FileSystemAccessRule to the security settings. 
            fSecurity.AddAccessRule(new FileSystemAccessRule(account, rights, controlType));
            //fSecurity.AddAccessRule(new FileSystemAccessRule(account, FileSystemRights.Delete, AccessControlType.Deny));

            // Set the new access settings.
            File.SetAccessControl(fileName, fSecurity);
        }

        // Removes an ACL entry on the specified file for the specified account.
        public static void RemoveFileSecurity(string fileName, string account,
            FileSystemRights rights, AccessControlType controlType)
        {
            // Get a FileSecurity object that represents the 
            // current security settings.
            FileSecurity fSecurity = File.GetAccessControl(fileName);

            // Add the FileSystemAccessRule to the security settings. 
            fSecurity.RemoveAccessRule(new FileSystemAccessRule(account,
                rights, controlType));

            // Set the new access settings.
            File.SetAccessControl(fileName, fSecurity);

        }

        public static void CreateUserAccount(string strMachineName, string strUserName, string strPassword)
        {
            Process process = new Process();
            process.StartInfo = new ProcessStartInfo("net.exe", string.Format("user {0} {1} /add", strUserName, strPassword))
                {
                    UseShellExecute = false
                };
            process.Start();
            process.WaitForExit();
        }

    }
}

注意：要设置的文件必须在切换登入用户之后再建立，也就是在ImpersonateUser()之后，才生成文件，否则在之后的File.SetAccessControl时候会出现没有授权的异常。