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

2 files changed, 7 insertions, 3 deletions

diff --git a/app/models/account.rb b/app/models/account.rb
index adf4586fa..ccd116d6e 100644
--- a/app/models/account.rb
+++ b/app/models/account.rb
@@ -77,7 +77,7 @@ class Account < ApplicationRecord
   validates :username, format: { with: /\A#{USERNAME_RE}\z/i }, if: -> { !local? && will_save_change_to_username? }
 
   # Local user validations
-  validates :username, format: { with: /\A[a-z0-9_]+\z/i }, length: { maximum: 30 }, if: -> { local? && will_save_change_to_username? }
+  validates :username, format: { with: /\A[a-z0-9_]+\z/i }, length: { maximum: 30 }, if: -> { local? && will_save_change_to_username? && actor_type != 'Application' }
   validates_with UniqueUsernameValidator, if: -> { local? && will_save_change_to_username? }
   validates_with UnreservedUsernameValidator, if: -> { local? && will_save_change_to_username? }
   validates :display_name, length: { maximum: 30 }, if: -> { local? && will_save_change_to_display_name? }
@@ -139,6 +139,10 @@ class Account < ApplicationRecord
     %w(Application Service).include? actor_type
   end
 
+  def instance_actor?
+    id == -99
+  end
+
   alias bot bot?
 
   def bot=(val)
@@ -498,7 +502,7 @@ class Account < ApplicationRecord
   end
 
   def generate_keys
-    return unless local? && !Rails.env.test?
+    return unless local? && private_key.blank? && public_key.blank?
 
     keypair = OpenSSL::PKey::RSA.new(2048)
     self.private_key = keypair.to_pem
diff --git a/app/models/concerns/account_finder_concern.rb b/app/models/concerns/account_finder_concern.rb
index ccd7bfa12..a54c2174d 100644
--- a/app/models/concerns/account_finder_concern.rb
+++ b/app/models/concerns/account_finder_concern.rb
@@ -13,7 +13,7 @@ module AccountFinderConcern
     end
 
     def representative
-      find_local(Setting.site_contact_username.strip.gsub(/\A@/, '')) || Account.local.without_suspended.first
+      Account.find(-99)
     end
 
     def find_local(username)