Add ActivityPub secure mode (#11269)

* Add HTTP signature requirement for served ActivityPub resources

* Change `SECURE_MODE` to `AUTHORIZED_FETCH`

* Add 'Signature' to 'Vary' header and improve code style

* Improve code style by adding `public_fetch_mode?` method

app/controllers/activitypub/inboxes_controller.rb

@@ -5,23 +5,24 @@ class ActivityPub::InboxesController < Api::BaseController
   include JsonLdHelper
   include AccountOwnedConcern
 
+  before_action :skip_unknown_actor_delete
+  before_action :require_signature!
+
   def create
-    if unknown_deleted_account?
-      head 202
-    elsif signed_request_account
-      upgrade_account
-      process_payload
-      head 202
-    else
-      render plain: signature_verification_failure_reason, status: 401
-    end
+    upgrade_account
+    process_payload
+    head 202
   end
 
   private
 
+  def skip_unknown_actor_delete
+    head 202 if unknown_deleted_account?
+  end
+
   def unknown_deleted_account?
     json = Oj.load(body, mode: :strict)
-    json['type'] == 'Delete' && json['actor'].present? && json['actor'] == value_or_id(json['object']) && !Account.where(uri: json['actor']).exists?
+    json.is_a?(Hash) && json['type'] == 'Delete' && json['actor'].present? && json['actor'] == value_or_id(json['object']) && !Account.where(uri: json['actor']).exists?
   rescue Oj::ParseError
     false
   end
@@ -32,8 +33,12 @@ class ActivityPub::InboxesController < Api::BaseController
 
   def body
     return @body if defined?(@body)
-    @body = request.body.read.force_encoding('UTF-8')
+
+    @body = request.body.read
+    @body.force_encoding('UTF-8') if @body.present?
+
     request.body.rewind if request.body.respond_to?(:rewind)
+
     @body
   end