Fix error when RFC9421 signatures are used (#35109)

app/controllers/concerns/signature_verification.rb

@@ -82,7 +82,7 @@ module SignatureVerification
   end
 
   def actor_from_key_id
-    key_id = signature_key_id
+    key_id = signed_request.key_id
     domain = key_id.start_with?('acct:') ? key_id.split('@').last : key_id
 
     if domain_not_allowed?(domain)

spec/requests/signature_verification_spec.rb

@@ -352,6 +352,33 @@ RSpec.describe 'signature verification concern' do
     end
   end
 
+  # TODO: Remove when feature is enabled
+  context 'with an HTTP Message Signature (final RFC version) when support is disabled' do
+    before { Fabricate(:account, domain: 'remote.domain', uri: 'https://remote.domain/users/bob', private_key: nil, public_key: actor_keypair.public_key.to_pem) }
+
+    context 'with a valid signature on a GET request' do
+      let(:signature_input) do
+        'sig1=("@method" "@target-uri");created=1703066400;keyid="https://remote.domain/users/bob#main-key"'
+      end
+      let(:signature_header) do
+        'sig1=:WfM6q/qBqhUyqPUDt9metjadJGtLLpmMTBzk/t+R3byKe4/TGAXC6vBB/M6NsD5qv8GCmQGtisCMQxJQO0IGODGzi+Jv+eqDJ50agMVXNV6nUOzY44c4/XTPoI98qyx1oEMa4Hefy3vSYKq96iDVAc+RDLCMTeGP3wn9wizjD1SNmU0RZI1bTB+eCkywMP9mM5zXzUOYF+Qkuf+WdEpPR1XUGPlnqfdvPalcKVfaI/VThBjI91D/lmUGoa69x4EBEHM+aJmW6086e7/dVh+FndKkdGfXslZXFZKi2flTGQZgEWLn948SqAaJQROkJg8B14Sb1NONS1qZBhK3Mum8Pg==:' # rubocop:disable Layout/LineLength
+      end
+
+      it 'cannot verify signature', :aggregate_failures do
+        get '/activitypub/signature_required', headers: {
+          'Host' => 'www.example.com',
+          'Signature-Input' => signature_input,
+          'Signature' => signature_header,
+        }
+
+        expect(response).to have_http_status(401)
+        expect(response.parsed_body).to match(
+          error: 'Error parsing signature parameters'
+        )
+      end
+    end
+  end
+
   context 'with an HTTP Message Signature (final RFC version)', feature: :http_message_signatures do
     context 'with a known account' do
       let!(:actor) { Fabricate(:account, domain: 'remote.domain', uri: 'https://remote.domain/users/bob', private_key: nil, public_key: actor_keypair.public_key.to_pem) }