If you want to monitor a web app it's probably only accessible after logging in. Login steps allow you to sign into a user account before the page is loaded for analysis.
When creating or editing a page, click "Show Advanced" and then select "Login Step".
From there you can select a login step, or create a new one.
To log into a user account the following information is needed:
After configuring the login step click "Update" to save your page changes.
When logging in your web server will most likely set a cookie that's necessary to access the data in the account. When loading a page archive these cookies are restored so that the front-end does not incorrectly think the user is unauthorized.