Load Test: Mimic multiple users to login to Silverlight Application

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.