Improvements to signature verification (#9667)

* Refactor signature verification a bit

* Rescue signature verification if recorded public key is invalid

Fixes #8822

* Always re-fetch AP signing key when HTTP Signature verification fails

But when the account is not marked as stale, avoid fetching collections and
media, and avoid webfinger round-trip.

* Apply stoplight to key/account update as well as initial key retrieval

2 files changed, 10 insertions, 8 deletions

diff --git a/app/services/activitypub/fetch_remote_account_service.rb b/app/services/activitypub/fetch_remote_account_service.rb
index 8430d12d5..3c2044941 100644
--- a/app/services/activitypub/fetch_remote_account_service.rb
+++ b/app/services/activitypub/fetch_remote_account_service.rb
@@ -5,8 +5,8 @@ class ActivityPub::FetchRemoteAccountService < BaseService
 
   SUPPORTED_TYPES = %w(Application Group Organization Person Service).freeze
 
-  # Does a WebFinger roundtrip on each call
-  def call(uri, id: true, prefetched_body: nil, break_on_redirect: false)
+  # 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)
     return ActivityPub::TagManager.instance.uri_to_resource(uri, Account) if ActivityPub::TagManager.instance.local_uri?(uri)
 
     @json = if prefetched_body.nil?
@@ -21,9 +21,9 @@ class ActivityPub::FetchRemoteAccountService < BaseService
     @username = @json['preferredUsername']
     @domain   = Addressable::URI.parse(@uri).normalized_host
 
-    return unless verified_webfinger?
+    return unless only_key || verified_webfinger?
 
-    ActivityPub::ProcessAccountService.new.call(@username, @domain, @json)
+    ActivityPub::ProcessAccountService.new.call(@username, @domain, @json, only_key: only_key)
   rescue Oj::ParseError
     nil
   end
diff --git a/app/services/activitypub/process_account_service.rb b/app/services/activitypub/process_account_service.rb
index d6480028f..d6c791b44 100644
--- a/app/services/activitypub/process_account_service.rb
+++ b/app/services/activitypub/process_account_service.rb
@@ -33,8 +33,10 @@ class ActivityPub::ProcessAccountService < BaseService
 
     after_protocol_change! if protocol_changed?
     after_key_change! if key_changed? && !@options[:signed_with_known_key]
-    check_featured_collection! if @account.featured_collection_url.present?
-    check_links! unless @account.fields.empty?
+    unless @options[:only_key]
+      check_featured_collection! if @account.featured_collection_url.present?
+      check_links! unless @account.fields.empty?
+    end
 
     @account
   rescue Oj::ParseError
@@ -54,11 +56,11 @@ class ActivityPub::ProcessAccountService < BaseService
   end
 
   def update_account
-    @account.last_webfingered_at = Time.now.utc
+    @account.last_webfingered_at = Time.now.utc unless @options[:only_key]
     @account.protocol            = :activitypub
 
     set_immediate_attributes!
-    set_fetchable_attributes!
+    set_fetchable_attributes! unless @options[:only_keys]
 
     @account.save_with_optional_media!
   end