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

app/views/about/more.html.haml

@@ -43,5 +43,7 @@
           = mail_to @instance_presenter.site_contact_email, nil, title: @instance_presenter.site_contact_email
 
   .column-3
+    = render 'application/flashes'
+
     .box-widget
       .rich-formatting= @instance_presenter.site_extended_description.html_safe.presence || t('about.extended_description_html')

app/views/well_known/webfinger/show.xml.ruby

@@ -4,30 +4,47 @@ doc << Ox::Element.new('XRD').tap do |xrd|
   xrd['xmlns'] = 'http://docs.oasis-open.org/ns/xri/xrd-1.0'
 
   xrd << (Ox::Element.new('Subject') << @account.to_webfinger_s)
-  xrd << (Ox::Element.new('Alias') << short_account_url(@account))
-  xrd << (Ox::Element.new('Alias') << account_url(@account))
 
-  xrd << Ox::Element.new('Link').tap do |link|
-    link['rel']      = 'http://webfinger.net/rel/profile-page'
-    link['type']     = 'text/html'
-    link['href']     = short_account_url(@account)
-  end
+  if @account.instance_actor?
+    xrd << (Ox::Element.new('Alias') << instance_actor_url)
 
-  xrd << Ox::Element.new('Link').tap do |link|
-    link['rel']      = 'http://schemas.google.com/g/2010#updates-from'
-    link['type']     = 'application/atom+xml'
-    link['href']     = account_url(@account, format: 'atom')
-  end
+    xrd << Ox::Element.new('Link').tap do |link|
+      link['rel']      = 'http://webfinger.net/rel/profile-page'
+      link['type']     = 'text/html'
+      link['href']     = about_more_url(instance_actor: true)
+    end
 
-  xrd << Ox::Element.new('Link').tap do |link|
-    link['rel']      = 'self'
-    link['type']     = 'application/activity+json'
-    link['href']     = account_url(@account)
-  end
+    xrd << Ox::Element.new('Link').tap do |link|
+      link['rel']      = 'self'
+      link['type']     = 'application/activity+json'
+      link['href']     = instance_actor_url
+    end
+  else
+    xrd << (Ox::Element.new('Alias') << short_account_url(@account))
+    xrd << (Ox::Element.new('Alias') << account_url(@account))
 
-  xrd << Ox::Element.new('Link').tap do |link|
-    link['rel']      = 'http://ostatus.org/schema/1.0/subscribe'
-    link['template'] = "#{authorize_interaction_url}?acct={uri}"
+    xrd << Ox::Element.new('Link').tap do |link|
+      link['rel']      = 'http://webfinger.net/rel/profile-page'
+      link['type']     = 'text/html'
+      link['href']     = short_account_url(@account)
+    end
+
+    xrd << Ox::Element.new('Link').tap do |link|
+      link['rel']      = 'http://schemas.google.com/g/2010#updates-from'
+      link['type']     = 'application/atom+xml'
+      link['href']     = account_url(@account, format: 'atom')
+    end
+
+    xrd << Ox::Element.new('Link').tap do |link|
+      link['rel']      = 'self'
+      link['type']     = 'application/activity+json'
+      link['href']     = account_url(@account)
+    end
+
+    xrd << Ox::Element.new('Link').tap do |link|
+      link['rel']      = 'http://ostatus.org/schema/1.0/subscribe'
+      link['template'] = "#{authorize_interaction_url}?acct={uri}"
+    end
   end
 end