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/controllers/accounts_controller.rb

@@ -7,7 +7,7 @@ class AccountsController < ApplicationController
   include AccountControllerConcern
   include SignatureAuthentication
 
-  before_action :require_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
+  before_action :require_account_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
   before_action :set_cache_headers
   before_action :set_body_classes
 

app/controllers/activitypub/claims_controller.rb

@@ -6,7 +6,7 @@ class ActivityPub::ClaimsController < ActivityPub::BaseController
 
   skip_before_action :authenticate_user!
 
-  before_action :require_signature!
+  before_action :require_account_signature!
   before_action :set_claim_result
 
   def create

app/controllers/activitypub/collections_controller.rb

@@ -4,7 +4,7 @@ class ActivityPub::CollectionsController < ActivityPub::BaseController
   include SignatureVerification
   include AccountOwnedConcern
 
-  before_action :require_signature!, if: :authorized_fetch_mode?
+  before_action :require_account_signature!, if: :authorized_fetch_mode?
   before_action :set_items
   before_action :set_size
   before_action :set_type

app/controllers/activitypub/followers_synchronizations_controller.rb

@@ -4,7 +4,7 @@ class ActivityPub::FollowersSynchronizationsController < ActivityPub::BaseContro
   include SignatureVerification
   include AccountOwnedConcern
 
-  before_action :require_signature!
+  before_action :require_account_signature!
   before_action :set_items
   before_action :set_cache_headers
 

app/controllers/activitypub/inboxes_controller.rb

@@ -6,7 +6,7 @@ class ActivityPub::InboxesController < ActivityPub::BaseController
   include AccountOwnedConcern
 
   before_action :skip_unknown_actor_activity
-  before_action :require_signature!
+  before_action :require_actor_signature!
   skip_before_action :authenticate_user!
 
   def create
@@ -49,17 +49,17 @@ class ActivityPub::InboxesController < ActivityPub::BaseController
   end
 
   def upgrade_account
-    if signed_request_account.ostatus?
+    if signed_request_account&.ostatus?
       signed_request_account.update(last_webfingered_at: nil)
       ResolveAccountWorker.perform_async(signed_request_account.acct)
     end
 
-    DeliveryFailureTracker.reset!(signed_request_account.inbox_url)
+    DeliveryFailureTracker.reset!(signed_request_actor.inbox_url)
   end
 
   def process_collection_synchronization
     raw_params = request.headers['Collection-Synchronization']
-    return if raw_params.blank? || ENV['DISABLE_FOLLOWERS_SYNCHRONIZATION'] == 'true'
+    return if raw_params.blank? || ENV['DISABLE_FOLLOWERS_SYNCHRONIZATION'] == 'true' || signed_request_account.nil?
 
     # Re-using the syntax for signature parameters
     tree   = SignatureParamsParser.new.parse(raw_params)
@@ -71,6 +71,6 @@ class ActivityPub::InboxesController < ActivityPub::BaseController
   end
 
   def process_payload
-    ActivityPub::ProcessingWorker.perform_async(signed_request_account.id, body, @account&.id)
+    ActivityPub::ProcessingWorker.perform_async(signed_request_actor.id, body, @account&.id, signed_request_actor.class.name)
   end
 end

app/controllers/activitypub/outboxes_controller.rb

@@ -6,7 +6,7 @@ class ActivityPub::OutboxesController < ActivityPub::BaseController
   include SignatureVerification
   include AccountOwnedConcern
 
-  before_action :require_signature!, if: :authorized_fetch_mode?
+  before_action :require_account_signature!, if: :authorized_fetch_mode?
   before_action :set_statuses
   before_action :set_cache_headers
 

app/controllers/activitypub/replies_controller.rb

@@ -7,7 +7,7 @@ class ActivityPub::RepliesController < ActivityPub::BaseController
 
   DESCENDANTS_LIMIT = 60
 
-  before_action :require_signature!, if: :authorized_fetch_mode?
+  before_action :require_account_signature!, if: :authorized_fetch_mode?
   before_action :set_status
   before_action :set_cache_headers
   before_action :set_replies

app/controllers/concerns/signature_verification.rb

@@ -45,10 +45,14 @@ module SignatureVerification
     end
   end
 
-  def require_signature!
+  def require_account_signature!
     render plain: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_account
   end
 
+  def require_actor_signature!
+    render plain: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_actor
+  end
+
   def signed_request?
     request.headers['Signature'].present?
   end
@@ -68,7 +72,11 @@ module SignatureVerification
   end
 
   def signed_request_account
-    return @signed_request_account if defined?(@signed_request_account)
+    signed_request_actor.is_a?(Account) ? signed_request_actor : nil
+  end
+
+  def signed_request_actor
+    return @signed_request_actor if defined?(@signed_request_actor)
 
     raise SignatureVerificationError, 'Request not signed' unless signed_request?
     raise SignatureVerificationError, 'Incompatible request signature. keyId and signature are required' if missing_required_signature_parameters?
@@ -78,22 +86,22 @@ module SignatureVerification
     verify_signature_strength!
     verify_body_digest!
 
-    account = account_from_key_id(signature_params['keyId'])
+    actor = actor_from_key_id(signature_params['keyId'])
 
-    raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if account.nil?
+    raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if actor.nil?
 
     signature             = Base64.decode64(signature_params['signature'])
     compare_signed_string = build_signed_string
 
-    return account unless verify_signature(account, signature, compare_signed_string).nil?
+    return actor unless verify_signature(actor, signature, compare_signed_string).nil?
 
-    account = stoplight_wrap_request { account.possibly_stale? ? account.refresh! : account_refresh_key(account) }
+    actor = stoplight_wrap_request { actor_refresh_key!(actor) }
 
-    raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if account.nil?
+    raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if actor.nil?
 
-    return account unless verify_signature(account, signature, compare_signed_string).nil?
+    return actor unless verify_signature(actor, signature, compare_signed_string).nil?
 
-    fail_with! "Verification failed for #{account.username}@#{account.domain} #{account.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)"
+    fail_with! "Verification failed for #{actor.to_log_human_identifier} #{actor.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)"
   rescue SignatureVerificationError => e
     fail_with! e.message
   rescue HTTP::Error, OpenSSL::SSL::SSLError => e
@@ -112,7 +120,7 @@ module SignatureVerification
 
   def fail_with!(message)
     @signature_verification_failure_reason = message
-    @signed_request_account = nil
+    @signed_request_actor = nil
   end
 
   def signature_params
@@ -160,10 +168,10 @@ module SignatureVerification
     raise SignatureVerificationError, "Invalid Digest value. Computed SHA-256 digest: #{body_digest}; given: #{sha256[1]}"
   end
 
-  def verify_signature(account, signature, compare_signed_string)
-    if account.keypair.public_key.verify(OpenSSL::Digest.new('SHA256'), signature, compare_signed_string)
-      @signed_request_account = account
-      @signed_request_account
+  def verify_signature(actor, signature, compare_signed_string)
+    if actor.keypair.public_key.verify(OpenSSL::Digest.new('SHA256'), signature, compare_signed_string)
+      @signed_request_actor = actor
+      @signed_request_actor
     end
   rescue OpenSSL::PKey::RSAError
     nil
@@ -226,7 +234,7 @@ module SignatureVerification
     signature_params['keyId'].blank? || signature_params['signature'].blank?
   end
 
-  def account_from_key_id(key_id)
+  def actor_from_key_id(key_id)
     domain = key_id.start_with?('acct:') ? key_id.split('@').last : key_id
 
     if domain_not_allowed?(domain)
@@ -237,13 +245,13 @@ module SignatureVerification
     if key_id.start_with?('acct:')
       stoplight_wrap_request { ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, ''), suppress_errors: false) }
     elsif !ActivityPub::TagManager.instance.local_uri?(key_id)
-      account   = ActivityPub::TagManager.instance.uri_to_resource(key_id, Account)
+      account   = ActivityPub::TagManager.instance.uri_to_actor(key_id)
       account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false, suppress_errors: false) }
       account
     end
   rescue Mastodon::PrivateNetworkAddressError => e
     raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})"
-  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteAccountService::Error, ActivityPub::FetchRemoteKeyService::Error, Webfinger::Error => e
+  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteActorService::Error, ActivityPub::FetchRemoteKeyService::Error, Webfinger::Error => e
     raise SignatureVerificationError, e.message
   end
 
@@ -255,12 +263,14 @@ module SignatureVerification
       .run
   end
 
-  def account_refresh_key(account)
-    return if account.local? || !account.activitypub?
-    ActivityPub::FetchRemoteAccountService.new.call(account.uri, only_key: true, suppress_errors: false)
+  def actor_refresh_key!(actor)
+    return if actor.local? || !actor.activitypub?
+    return actor.refresh! if actor.respond_to?(:refresh!) && actor.possibly_stale?
+
+    ActivityPub::FetchRemoteActorService.new.call(actor.uri, only_key: true, suppress_errors: false)
   rescue Mastodon::PrivateNetworkAddressError => e
     raise SignatureVerificationError, "Requests to private network addresses are disallowed (tried to query #{e.host})"
-  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteAccountService::Error, Webfinger::Error => e
+  rescue Mastodon::HostValidationError, ActivityPub::FetchRemoteActorService::Error, Webfinger::Error => e
     raise SignatureVerificationError, e.message
   end
 end

app/controllers/follower_accounts_controller.rb

@@ -4,7 +4,7 @@ class FollowerAccountsController < ApplicationController
   include AccountControllerConcern
   include SignatureVerification
 
-  before_action :require_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
+  before_action :require_account_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
   before_action :set_cache_headers
 
   skip_around_action :set_locale, if: -> { request.format == :json }

app/controllers/following_accounts_controller.rb

@@ -4,7 +4,7 @@ class FollowingAccountsController < ApplicationController
   include AccountControllerConcern
   include SignatureVerification
 
-  before_action :require_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
+  before_action :require_account_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
   before_action :set_cache_headers
 
   skip_around_action :set_locale, if: -> { request.format == :json }

app/controllers/statuses_controller.rb

@@ -8,7 +8,7 @@ class StatusesController < ApplicationController
 
   layout 'public'
 
-  before_action :require_signature!, only: [:show, :activity], if: -> { request.format == :json && authorized_fetch_mode? }
+  before_action :require_account_signature!, only: [:show, :activity], if: -> { request.format == :json && authorized_fetch_mode? }
   before_action :set_status
   before_action :set_instance_presenter
   before_action :set_link_headers

app/controllers/tags_controller.rb

@@ -8,7 +8,7 @@ class TagsController < ApplicationController
 
   layout 'public'
 
-  before_action :require_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
+  before_action :require_account_signature!, if: -> { request.format == :json && authorized_fetch_mode? }
   before_action :authenticate_user!, if: :whitelist_mode?
   before_action :set_local
   before_action :set_tag

app/lib/activitypub/activity.rb

@@ -116,12 +116,12 @@ class ActivityPub::Activity
   def dereference_object!
     return unless @object.is_a?(String)
 
-    dereferencer = ActivityPub::Dereferencer.new(@object, permitted_origin: @account.uri, signature_account: signed_fetch_account)
+    dereferencer = ActivityPub::Dereferencer.new(@object, permitted_origin: @account.uri, signature_actor: signed_fetch_actor)
 
     @object = dereferencer.object unless dereferencer.object.nil?
   end
 
-  def signed_fetch_account
+  def signed_fetch_actor
     return Account.find(@options[:delivered_to_account_id]) if @options[:delivered_to_account_id].present?
 
     first_mentioned_local_account || first_local_follower
@@ -163,15 +163,15 @@ class ActivityPub::Activity
   end
 
   def followed_by_local_accounts?
-    @account.passive_relationships.exists? || @options[:relayed_through_account]&.passive_relationships&.exists?
+    @account.passive_relationships.exists? || (@options[:relayed_through_actor].is_a?(Account) && @options[:relayed_through_actor].passive_relationships&.exists?)
   end
 
   def requested_through_relay?
-    @options[:relayed_through_account] && Relay.find_by(inbox_url: @options[:relayed_through_account].inbox_url)&.enabled?
+    @options[:relayed_through_actor] && Relay.find_by(inbox_url: @options[:relayed_through_actor].inbox_url)&.enabled?
   end
 
   def reject_payload!
-    Rails.logger.info("Rejected #{@json['type']} activity #{@json['id']} from #{@account.uri}#{@options[:relayed_through_account] && "via #{@options[:relayed_through_account].uri}"}")
+    Rails.logger.info("Rejected #{@json['type']} activity #{@json['id']} from #{@account.uri}#{@options[:relayed_through_actor] && "via #{@options[:relayed_through_actor].uri}"}")
     nil
   end
 end

app/lib/activitypub/dereferencer.rb

@@ -3,10 +3,10 @@
 class ActivityPub::Dereferencer
   include JsonLdHelper
 
-  def initialize(uri, permitted_origin: nil, signature_account: nil)
+  def initialize(uri, permitted_origin: nil, signature_actor: nil)
     @uri               = uri
     @permitted_origin  = permitted_origin
-    @signature_account = signature_account
+    @signature_actor = signature_actor
   end
 
   def object
@@ -46,7 +46,7 @@ class ActivityPub::Dereferencer
 
     req.add_headers('Accept' => 'application/activity+json, application/ld+json')
     req.add_headers(headers) if headers
-    req.on_behalf_of(@signature_account) if @signature_account
+    req.on_behalf_of(@signature_actor) if @signature_actor
 
     req.perform do |res|
       if res.code == 200

app/lib/activitypub/linked_data_signature.rb

@@ -9,7 +9,7 @@ class ActivityPub::LinkedDataSignature
     @json = json.with_indifferent_access
   end
 
-  def verify_account!
+  def verify_actor!
     return unless @json['signature'].is_a?(Hash)
 
     type        = @json['signature']['type']
@@ -18,7 +18,7 @@ class ActivityPub::LinkedDataSignature
 
     return unless type == 'RsaSignature2017'
 
-    creator   = ActivityPub::TagManager.instance.uri_to_resource(creator_uri, Account)
+    creator   = ActivityPub::TagManager.instance.uri_to_actor(creator_uri)
     creator ||= ActivityPub::FetchRemoteKeyService.new.call(creator_uri, id: false)
 
     return if creator.nil?
@@ -35,7 +35,7 @@ class ActivityPub::LinkedDataSignature
   def sign!(creator, sign_with: nil)
     options = {
       'type'    => 'RsaSignature2017',
-      'creator' => [ActivityPub::TagManager.instance.uri_for(creator), '#main-key'].join,
+      'creator' => ActivityPub::TagManager.instance.key_uri_for(creator),
       'created' => Time.now.utc.iso8601,
     }
 

app/lib/activitypub/tag_manager.rb

@@ -44,6 +44,10 @@ class ActivityPub::TagManager
     end
   end
 
+  def key_uri_for(target)
+    [uri_for(target), '#main-key'].join
+  end
+
   def uri_for_username(username)
     account_url(username: username)
   end
@@ -155,6 +159,10 @@ class ActivityPub::TagManager
     path_params[param]
   end
 
+  def uri_to_actor(uri)
+    uri_to_resource(uri, Account)
+  end
+
   def uri_to_resource(uri, klass)
     return if uri.nil?
 

app/lib/request.rb

@@ -40,12 +40,11 @@ class Request
     set_digest! if options.key?(:body)
   end
 
-  def on_behalf_of(account, key_id_format = :uri, sign_with: nil)
-    raise ArgumentError, 'account must not be nil' if account.nil?
+  def on_behalf_of(actor, sign_with: nil)
+    raise ArgumentError, 'actor must not be nil' if actor.nil?
 
-    @account       = account
-    @keypair       = sign_with.present? ? OpenSSL::PKey::RSA.new(sign_with) : @account.keypair
-    @key_id_format = key_id_format
+    @actor         = actor
+    @keypair       = sign_with.present? ? OpenSSL::PKey::RSA.new(sign_with) : @actor.keypair
 
     self
   end
@@ -79,7 +78,7 @@ class Request
   end
 
   def headers
-    (@account ? @headers.merge('Signature' => signature) : @headers).without(REQUEST_TARGET)
+    (@actor ? @headers.merge('Signature' => signature) : @headers).without(REQUEST_TARGET)
   end
 
   class << self
@@ -128,12 +127,7 @@ class Request
   end
 
   def key_id
-    case @key_id_format
-    when :acct
-      @account.to_webfinger_s
-    when :uri
-      [ActivityPub::TagManager.instance.uri_for(@account), '#main-key'].join
-    end
+    ActivityPub::TagManager.instance.key_uri_for(@actor)
   end
 
   def http_client

app/serializers/activitypub/public_key_serializer.rb

@@ -6,7 +6,7 @@ class ActivityPub::PublicKeySerializer < ActivityPub::Serializer
   attributes :id, :owner, :public_key_pem
 
   def id
-    [ActivityPub::TagManager.instance.uri_for(object), '#main-key'].join
+    ActivityPub::TagManager.instance.key_uri_for(object)
   end
 
   def owner

app/services/activitypub/fetch_remote_account_service.rb

 # 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)
-
-    @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
+    actor = super
+    return actor if actor.nil? || actor.is_a?(Account)
 
-  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

app/services/activitypub/fetch_remote_actor_service.rb

+# frozen_string_literal: true
+
+class ActivityPub::FetchRemoteActorService < BaseService
+  include JsonLdHelper
+  include DomainControlHelper
+  include WebfingerHelper
+
+  class Error < StandardError; end
+
+  SUPPORTED_TYPES = %w(Application Group Organization Person Service).freeze
+
+  # 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_actor(uri) if ActivityPub::TagManager.instance.local_uri?(uri)
+
+    @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 actor #{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)
+  end
+end