未经测试的代码，但将类似于：

AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);

// http://pinvoke.net/default.aspx/advapi32/LogonUser.html    
IntPtr token;
LogonUser("username", "domain", "password", LogonType.LOGON32_LOGON_BATCH, LogonProvider.LOGON32_PROVIDER_DEFAULT);

WindowsIdentity identity = new WindowsIdentity(token);

WindowsImpersonationContext context = identity.Impersonate();

try
{
    File.Copy(@"c:\temp\MyFile.txt", @"\\server\folder\Myfile.txt", true);
}
finally
{
    context.Undo();
}