To add an extra layer of security, we sanitize settings before shipping them to the client. We don't sanitize those that have the "html" type.
The CookedPostProcessor already uses Loofah for sanitization, so I chose to also use it for this. I added it to our gemfile since we installed it as a transitive dependency.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
