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

1 files changed, 20 insertions, 0 deletions

diff --git a/app/controllers/instance_actors_controller.rb b/app/controllers/instance_actors_controller.rb
new file mode 100644
index 000000000..41f33602e
--- /dev/null
+++ b/app/controllers/instance_actors_controller.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class InstanceActorsController < ApplicationController
+  include AccountControllerConcern
+
+  def show
+    expires_in 10.minutes, public: true
+    render json: @account, content_type: 'application/activity+json', serializer: ActivityPub::ActorSerializer, adapter: ActivityPub::Adapter, fields: restrict_fields_to
+  end
+
+  private
+
+  def set_account
+    @account = Account.find(-99)
+  end
+
+  def restrict_fields_to
+    %i(id type preferred_username inbox public_key endpoints url manually_approves_followers)
+  end
+end