Refactor ActivityPub handling to prepare for non-Account actors (#19212)

* Move ActivityPub::FetchRemoteAccountService to ActivityPub::FetchRemoteActorService

ActivityPub::FetchRemoteAccountService is kept as a wrapper for when the actor is
specifically required to be an Account

* Refactor SignatureVerification to allow non-Account actors

* fixup! Move ActivityPub::FetchRemoteAccountService to ActivityPub::FetchRemoteActorService

* Refactor ActivityPub::FetchRemoteKeyService to potentially return non-Account actors

* Refactor inbound ActivityPub payload processing to accept non-Account actors

* Refactor inbound ActivityPub processing to accept activities relayed through non-Account

* Refactor how Account key URIs are built

* Refactor Request and drop unused key_id_format parameter

* Rename ActivityPub::Dereferencer `signature_account` to `signature_actor`

app/services/activitypub/fetch_remote_account_service.rb

@@ -1,80 +1,12 @@
 # frozen_string_literal: true
 
-class ActivityPub::FetchRemoteAccountService < BaseService
-  include JsonLdHelper
-  include DomainControlHelper
-  include WebfingerHelper
-
-  class Error < StandardError; end
-
-  SUPPORTED_TYPES = %w(Application Group Organization Person Service).freeze
-
+class ActivityPub::FetchRemoteAccountService < ActivityPub::FetchRemoteActorService
   # Does a WebFinger roundtrip on each call, unless `only_key` is true
   def call(uri, id: true, prefetched_body: nil, break_on_redirect: false, only_key: false, suppress_errors: true)
-    return if domain_not_allowed?(uri)
-    return ActivityPub::TagManager.instance.uri_to_resource(uri, Account) if ActivityPub::TagManager.instance.local_uri?(uri)
+    actor = super
+    return actor if actor.nil? || actor.is_a?(Account)
 
-    @json = begin
-      if prefetched_body.nil?
-        fetch_resource(uri, id)
-      else
-        body_to_json(prefetched_body, compare_id: id ? uri : nil)
-      end
-    rescue Oj::ParseError
-      raise Error, "Error parsing JSON-LD document #{uri}"
-    end
-
-    raise Error, "Error fetching actor JSON at #{uri}" if @json.nil?
-    raise Error, "Unsupported JSON-LD context for document #{uri}" unless supported_context?
-    raise Error, "Unexpected object type for actor #{uri} (expected any of: #{SUPPORTED_TYPES})" unless expected_type?
-    raise Error, "Actor #{uri} has moved to #{@json['movedTo']}" if break_on_redirect && @json['movedTo'].present?
-
-    @uri      = @json['id']
-    @username = @json['preferredUsername']
-    @domain   = Addressable::URI.parse(@uri).normalized_host
-
-    check_webfinger! unless only_key
-
-    ActivityPub::ProcessAccountService.new.call(@username, @domain, @json, only_key: only_key, verified_webfinger: !only_key)
-  rescue Error => e
-    Rails.logger.debug "Fetching account #{uri} failed: #{e.message}"
-    raise unless suppress_errors
-  end
-
-  private
-
-  def check_webfinger!
-    webfinger                            = webfinger!("acct:#{@username}@#{@domain}")
-    confirmed_username, confirmed_domain = split_acct(webfinger.subject)
-
-    if @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
-      raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
-      return
-    end
-
-    webfinger                            = webfinger!("acct:#{confirmed_username}@#{confirmed_domain}")
-    @username, @domain                   = split_acct(webfinger.subject)
-
-    unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
-      raise Webfinger::RedirectError, "Too many webfinger redirects for URI #{uri} (stopped at #{@username}@#{@domain})"
-    end
-
-    raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
-  rescue Webfinger::RedirectError => e
-    raise Error, e.message
-  rescue Webfinger::Error => e
-    raise Error, "Webfinger error when resolving #{@username}@#{@domain}: #{e.message}"
-  end
-
-  def split_acct(acct)
-    acct.gsub(/\Aacct:/, '').split('@')
-  end
-
-  def supported_context?
-    super(@json)
-  end
-
-  def expected_type?
-    equals_or_includes_any?(@json['type'], SUPPORTED_TYPES)
+    Rails.logger.debug "Fetching account #{uri} failed: Expected Account, got #{actor.class.name}"
+    raise Error, "Expected Account, got #{actor.class.name}" unless suppress_errors
   end
 end