Cache JSON of immutable ActivityPub representations (#6171)

app/controllers/application_controller.rb

@@ -123,11 +123,23 @@ class ApplicationController < ActionController::Base
   end
 
   def render_cached_json(cache_key, **options)
+    options[:expires_in] ||= 3.minutes
+    cache_key              = cache_key.join(':') if cache_key.is_a?(Enumerable)
+    content_type           = options.delete(:content_type) || 'application/json'
+
     data = Rails.cache.fetch(cache_key, { raw: true }.merge(options)) do
       yield.to_json
     end
 
     expires_in options[:expires_in], public: true
-    render json: data
+    render json: data, content_type: content_type
+  end
+
+  def set_cache_headers
+    response.headers['Vary'] = 'Accept'
+  end
+
+  def skip_session!
+    request.session_options[:skip] = true
   end
 end