I use my work laptop to hit our Silverlight Application via my credential automatically. Therefore, I cannot see the Windows Authentication popup.
If I would like to mimic multiple test users to login to Silverlight Application via different credential, how can I do that? It is pretty easy.
Open IE-> Internet Options-> Security-> Custom Levels -> Check Prompt for user name and password inside User Authentication.
Put 20 different usernames with passwords in the file.
Open Visual studio IDE.
Create a new web performance test that can randomly pick up the different user to login to Silverlight Application.
Create a Load test that adds this web performance test.
Run the load test and you are all set.