Add ActivityPub secure mode (#11269)

* Add HTTP signature requirement for served ActivityPub resources

* Change `SECURE_MODE` to `AUTHORIZED_FETCH`

* Add 'Signature' to 'Vary' header and improve code style

* Improve code style by adding `public_fetch_mode?` method

2 files changed, 17 insertions, 4 deletions

diff --git a/app/controllers/concerns/account_controller_concern.rb b/app/controllers/concerns/account_controller_concern.rb
index 287a930da..11eac0eb6 100644
--- a/app/controllers/concerns/account_controller_concern.rb
+++ b/app/controllers/concerns/account_controller_concern.rb
@@ -11,7 +11,7 @@ module AccountControllerConcern
     layout 'public'
 
     before_action :set_instance_presenter
-    before_action :set_link_headers
+    before_action :set_link_headers, if: -> { request.format.nil? || request.format == :html }
   end
 
   private
diff --git a/app/controllers/concerns/signature_verification.rb b/app/controllers/concerns/signature_verification.rb
index 0ccdf5ec9..7b251cf80 100644
--- a/app/controllers/concerns/signature_verification.rb
+++ b/app/controllers/concerns/signature_verification.rb
@@ -7,12 +7,20 @@ module SignatureVerification
 
   include DomainControlHelper
 
+  def require_signature!
+    render plain: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_account
+  end
+
   def signed_request?
     request.headers['Signature'].present?
   end
 
   def signature_verification_failure_reason
-    return @signature_verification_failure_reason if defined?(@signature_verification_failure_reason)
+    @signature_verification_failure_reason
+  end
+
+  def signature_verification_failure_code
+    @signature_verification_failure_code || 401
   end
 
   def signed_request_account
@@ -125,11 +133,16 @@ module SignatureVerification
   end
 
   def account_from_key_id(key_id)
+    domain = key_id.start_with?('acct:') ? key_id.split('@').last : key_id
+
+    if domain_not_allowed?(domain)
+      @signature_verification_failure_code = 403
+      return
+    end
+
     if key_id.start_with?('acct:')
       stoplight_wrap_request { ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, '')) }
     elsif !ActivityPub::TagManager.instance.local_uri?(key_id)
-      return if domain_not_allowed?(key_id)
-
       account   = ActivityPub::TagManager.instance.uri_to_resource(key_id, Account)
       account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false) }
       account