Allow to dereference Follow object for ActivityPub (#5772)

* Allow to dereference Follow object for ActivityPub

* Accept IRI as object representation for Accept activity

app/lib/activitypub/activity/accept.rb

@@ -2,16 +2,18 @@
 
 class ActivityPub::Activity::Accept < ActivityPub::Activity
   def perform
-    case @object['type']
-    when 'Follow'
-      accept_follow
+    if @object.respond_to?(:[]) &&
+       @object['type'] == 'Follow' && @object['actor'].present?
+      accept_follow_from @object['actor']
+    else
+      accept_follow_object @object
     end
   end
 
   private
 
-  def accept_follow
-    target_account = account_from_uri(target_uri)
+  def accept_follow_from(actor)
+    target_account = account_from_uri(value_or_id(actor))
 
     return if target_account.nil? || !target_account.local?
 
@@ -19,7 +21,8 @@ class ActivityPub::Activity::Accept < ActivityPub::Activity
     follow_request&.authorize!
   end
 
-  def target_uri
-    @target_uri ||= value_or_id(@object['actor'])
+  def accept_follow_object(object)
+    follow_request = ActivityPub::TagManager.instance.uri_to_resource(value_or_id(object), FollowRequest)
+    follow_request&.authorize!
   end
 end

app/lib/activitypub/tag_manager.rb

@@ -28,6 +28,8 @@ class ActivityPub::TagManager
     return target.uri if target.respond_to?(:local?) && !target.local?
 
     case target.object_type
+    when :follow
+      account_follow_url(target.account.username, target)
     when :person
       account_url(target)
     when :note, :comment, :activity
@@ -97,6 +99,12 @@ class ActivityPub::TagManager
       case klass.name
       when 'Account'
         klass.find_local(uri_to_local_id(uri, :username))
+      when 'FollowRequest'
+        params = Rails.application.routes.recognize_path(uri)
+        klass.joins(:account).find_by!(
+          accounts: { domain: nil, username: params[:account_username] },
+          id: params[:id]
+        )
       else
         StatusFinder.new(uri).status
       end