Just place this widget in your Header and set the site property True.

It will create users for each Role that is used inside the current application and populate the  combobox. 

You can use the combobox to select your desired TestUser and click login.

This widget makes it very easy to test the different roles inside an application.

I recommend to place the widget inside an IF and connect it to a site property so you can disable it for just your application. The site property of the widget itself is meant to disable it in the production environment.