Authenticating windows users from a JS application on the internet

We have a mobile application written in JS. We need the user to enter their active directory (windows) credentials in the JS page and send the data via SSL to our services for authentication. I'm not sure what the best way to do this. I was looking at XMLHttpRequest on the JS side, but when the call is made to an aspx page for example, I don't have access to the login\password data passed in except for looking at the Request object which we don't want to do because we don't want to have access to user's passwords.

I'm looking for a way to post the credentials and have IIS or ASP.NET perform the authentication without any coding on our end. If successful, we would allocate a guid to the user to use for any future calls.

Thanks
Alex