secure area uses hardcoded domain

[duncdrum]

Is your feature request related to a problem? Please describe.
currently there is a universal org.exist-db.mysec.user domain. This not necessarily what users want.

Describe the solution you'd like
Let's make the domain dynamic based on the app namespace domain (which already has a prompt). This requires edits to page.html, config.xqm, and 2x controller.xql