I have a web application that uses the asp.net membership and role providers to allow logins that are members of certain roles to have access to various pages depending on
As an alternative there exists also tools like Selenium IDE which is a plugin for Firefox. Its main purpose is to provide some kind of testing for UIs. For this purpose you can record actions that are done on the UI. What you could do is to record the credentials you enter for the test-user once and save them. The next time you come back, you execute the script which automatically fills in the necessary information.
There are other tools which are specialized for the purpose of auto-filling a form on a webpage. Selenium is more thought as a testing evironment, but I've also used it for such purposes. Of course this is just a workaround.