Catch Failed IIS Windows Authentication

[Jared]

Hi

I am developing an intranet based ASP.NET application. Due to high
security on site the application needs to run accross two separate
domains (only http and https ports are open). The application
autenticates users via a form and security info is held in a database
table.

When users are on either domain they have the same windows username,
but the application server is only running on one domain.

To save a little time I would like to grab the Windows user ID where
ever possible and populate the logon form. This works fine on the
domain that the application is installed on using Windows
Authentication in IIS, but when the appliacation runs on the other
domain I get the annoying Windows Authentication dialogue box.

Is there any way to catch when automatic authentication has failed and
therefore stop showing the IIS dialogue, but still capture the current
windows username? I have searched in vain for client-side script to
capture the user id.

This is only a nice to have, but it would be a shame if I can't have
the same functionality as I do in old-fashioned client-server
applications.

Thanks

Jared