Our appliation uses an ajax query to validate users and login. It doesn't look like there is a way to use dynamic values for the username/password in this scenario since those values are not passed in via querystring (see the right side of the screenshot where the data passed in has the username/password).
It also doesn't seem like the custom cookie feature can be bound to dynamic values from excel.
Is there any other way or workarounds to do load testing for mass users for a web app? Any help would be greatly appreciated!