discourse/config/initializers/99-anon-cache.rb

require_dependency "middleware/anonymous_cache"

enabled = if Rails.configuration.respond_to?(:enable_anon_caching)
            Rails.configuration.enable_anon_caching
          else
            Rails.env.production?
          end

if !ENV['DISCOURSE_DISABLE_ANON_CACHE'] && enabled
  # in an ideal world this is position 0, but mobile detection uses ... session and request and params
  Rails.configuration.middleware.insert_after ActionDispatch::ParamsParser, Middleware::AnonymousCache
end