Add ActivityPub actor representing the entire server (#11321)

* Add support for an instance actor

* Skip username validation for local Application accounts

* Add migration script to create instance actor

* Make Codeclimate happy

* Switch to id -99 for instance actor

* Remove unused `icon` and `image` attributes from instance actor

* Use if/elsif/else instead of return + ternary operator

* Add instance actor to fresh installs

* Use instance actor as instance representative

Use instance actor for forwarding reports, relay operations, and spam
auto-reporting.

* Seed database in test environment

* Fix single-user mode

* Fix tests

* Fix specs to accomodate for an extra `Account`

* Auto-reject follows on instance actor

Following an instance actor might make sense, but we are not handling that
right now, so auto-reject.

* Fix webfinger lookup and serialization for instance actor

* Rename instance actor

* Make it clear in the HTML view that the instance actor should not be blocked

* Raise cache time for instance actor as there's no dynamic content

* Re-use /about/more with a flash message for instance actor profile

3 files changed, 10 insertions, 3 deletions

diff --git a/app/lib/activitypub/activity/follow.rb b/app/lib/activitypub/activity/follow.rb
index 3eb88339aeb..28f1da19f89 100644
--- a/app/lib/activitypub/activity/follow.rb
+++ b/app/lib/activitypub/activity/follow.rb
@@ -8,7 +8,7 @@ class ActivityPub::Activity::Follow < ActivityPub::Activity
 
     return if target_account.nil? || !target_account.local? || delete_arrived_first?(@json['id']) || @account.requested?(target_account)
 
-    if target_account.blocking?(@account) || target_account.domain_blocking?(@account.domain) || target_account.moved?
+    if target_account.blocking?(@account) || target_account.domain_blocking?(@account.domain) || target_account.moved? || target_account.instance_actor?
       reject_follow_request!(target_account)
       return
     end
diff --git a/app/lib/activitypub/tag_manager.rb b/app/lib/activitypub/tag_manager.rb
index 4d452f290ba..512272dbebe 100644
--- a/app/lib/activitypub/tag_manager.rb
+++ b/app/lib/activitypub/tag_manager.rb
@@ -17,7 +17,7 @@ class ActivityPub::TagManager
 
     case target.object_type
     when :person
-      short_account_url(target)
+      target.instance_actor? ? about_more_url(instance_actor: true) : short_account_url(target)
     when :note, :comment, :activity
       return activity_account_status_url(target.account, target) if target.reblog?
       short_account_status_url(target.account, target)
@@ -29,7 +29,7 @@ class ActivityPub::TagManager
 
     case target.object_type
     when :person
-      account_url(target)
+      target.instance_actor? ? instance_actor_url : account_url(target)
     when :note, :comment, :activity
       return activity_account_status_url(target.account, target) if target.reblog?
       account_status_url(target.account, target)
@@ -119,6 +119,7 @@ class ActivityPub::TagManager
 
   def uri_to_local_id(uri, param = :id)
     path_params = Rails.application.routes.recognize_path(uri)
+    path_params[:username] = Rails.configuration.x.local_domain if path_params[:controller] == 'instance_actors'
     path_params[param]
   end
 
diff --git a/app/lib/webfinger_resource.rb b/app/lib/webfinger_resource.rb
index a54a702a2e9..22d78874a4b 100644
--- a/app/lib/webfinger_resource.rb
+++ b/app/lib/webfinger_resource.rb
@@ -23,11 +23,17 @@ class WebfingerResource
   def username_from_url
     if account_show_page?
       path_params[:username]
+    elsif instance_actor_page?
+      Rails.configuration.x.local_domain
     else
       raise ActiveRecord::RecordNotFound
     end
   end
 
+  def instance_actor_page?
+    path_params[:controller] == 'instance_actors'
+  end
+
   def account_show_page?
     path_params[:controller] == 'accounts' && path_params[:action] == 'show'
   end