How to improve the security on a ASP.NET site?
<p>I have an ASP.NET site and some clients want a better layer of security for accessing it. The site today asks for a username and password, but a lot of clients want to restrict the access to some machines and I need to do this on my server side. So, I'm asking for some advice.</p>

<ol>
<li><p>Use a VPN to restrict the access? (With mobile devices will not work)</p></li>
<li><p>Is possible to check the mac address?</p></li>
<li><p>Is possible to use client certificate?</p></li>
</ol>
