Update the Authentication Settings page for modern subform support.

Review Request #11063 — Created July 3, 2020 and submitted — Latest diff uploaded


Review Board


The Authentication Settings page has been updated to work with the
subform support introduced in Review Board 4.0. This gives us a
maintainable way of allowing authentication forms to be added to the
page and configured without triggering any browser-side validation
issues for unselected subforms.

As part of this, the base admin/settings.html template has been
set up to load in subforms. This will be necessary for upcoming changes
for other settings forms.

Tested saving the authentication form with each subform selection. Verified
that only the selected subforms received any client-side or server-side
validation, and that settings loaded.