title: How to authenticate users from another domain in an ASP.NET SaaS application?
body: <p>We have an ASP.NET web application that we offer as a Service (it's hosted and it's accessible on the Web). We use Forms Authentication and our users have to enter a username/password to connect to our application. Some of our customers ask that we support single sign-on by authenticating users with their own Active Directory.</p>
  
  <p>Our application has a different URL for each customer</p>
  
  <pre><code>www.ourapp.com/client1/
  www.ourapp.com/client2/
  www.ourapp.com/client3/
  </code></pre>
  
  <p>and each URL has its own web.config file (where asp.net settings can be specified and can vary for each customer).</p>
  
  <ul>
  <li>What do I have to change in my ASP.NET application to support that? </li>
  <li>What do I have to change on my Windows server configuration? </li>
  <li>What will the customer have to do on his side to enable that?</li>
  </ul>
  
  <p>Regards,</p>