Fix /api/v1/instance/domain_blocks being unconditionally cached (#24662)

app/controllers/api/v1/instances/domain_blocks_controller.rb

@@ -6,10 +6,15 @@ class Api::V1::Instances::DomainBlocksController < Api::BaseController
   before_action :require_enabled_api!
   before_action :set_domain_blocks
 
-  vary_by ''
+  vary_by '', if: -> { Setting.show_domain_blocks == 'all' }
 
   def index
-    cache_even_if_authenticated!
+    if Setting.show_domain_blocks == 'all'
+      cache_even_if_authenticated!
+    else
+      cache_if_unauthenticated!
+    end
+
     render json: @domain_blocks, each_serializer: REST::DomainBlockSerializer, with_comment: (Setting.show_domain_blocks_rationale == 'all' || (Setting.show_domain_blocks_rationale == 'users' && user_signed_in?))
   end
 

app/controllers/concerns/cache_concern.rb

@@ -156,8 +156,8 @@ module CacheConcern
   end
 
   class_methods do
-    def vary_by(value)
-      before_action do |controller|
+    def vary_by(value, **kwargs)
+      before_action(**kwargs) do |controller|
         response.headers['Vary'] = value.respond_to?(:call) ? controller.instance_exec(&value) : value
       end
     end