This new setting allows you to add a list of comma delimited groups to
the allow list.
Previous to this change auth proxy was able to authenticate admins OR
all users on the site, without any fidelity of allowing specific groups.
This also refactors the tests somewhat and adds a bunch of integration
tests to ensure the new setting is properly respected.
Co-authored-by: Saj Goonatilleke <saj@discourse.org>
Sam Saffron