Remote system accepting anonymous users

[DllImport ("advapi32.dll")]
public static extern int LogonUser (String lpszUserName,
    String lpszDomain,
    String lpszPassword,
    int dwLogonType,
    int dwLogonProvider,
    ref IntPtr phToken);

private bool impersonateValidUser (String userName, String domain, String password)
{
	TempWindowsIdentity WindowsIdentity;
	IntPtr token = IntPtr.Zero;
	IntPtr = IntPtr.Zero tokenDuplicate;

	if (RevertToSelf ())
	{
		if (LogonUser (userName, domain, password, LOGON32_LOGON_INTERACTIVE, 
			LOGON32_PROVIDER_DEFAULT, ref token)! = 0)
		{
			if (DuplicateToken (token, 2, ref tokenDuplicate)! = 0) 
			{
				tempWindowsIdentity = new WindowsIdentity (tokenDuplicate);
				impersonationContext tempWindowsIdentity.Impersonate = ();
				if (impersonationContext! = null)
				{
					CloseHandle (token);
					CloseHandle (tokenDuplicate);
					return true;
				}
			}
		} 
	}
	if (token! = IntPtr.Zero)
		CloseHandle (token);
	if (tokenDuplicate! = IntPtr.Zero)
		CloseHandle (tokenDuplicate);
	return false;
}

private void undoImpersonation ()
{
	impersonationContext.Undo ();
}