Add more specific error messages to HTTP signature verification (#21617)

* Return specific error on failure to parse Date header

* Add error message when preferredUsername is not set

* Change error report to be JSON and include more details

* Change error report to differentiate unknown account and failed refresh

* Add tests

app/controllers/concerns/signature_verification.rb

@@ -46,11 +46,11 @@ module SignatureVerification
   end
 
   def require_account_signature!
-    render plain: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_account
+    render json: 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
+    render json: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_actor
   end
 
   def signed_request?
@@ -97,11 +97,11 @@ module SignatureVerification
 
     actor = stoplight_wrap_request { actor_refresh_key!(actor) }
 
-    raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if actor.nil?
+    raise SignatureVerificationError, "Could not refresh public key #{signature_params['keyId']}" if actor.nil?
 
     return actor unless verify_signature(actor, signature, compare_signed_string).nil?
 
-    fail_with! "Verification failed for #{actor.to_log_human_identifier} #{actor.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)", signed_string: compare_signed_string, signature: signature_params['signature']
   rescue SignatureVerificationError => e
     fail_with! e.message
   rescue HTTP::Error, OpenSSL::SSL::SSLError => e
@@ -118,8 +118,8 @@ module SignatureVerification
 
   private
 
-  def fail_with!(message)
-    @signature_verification_failure_reason = message
+  def fail_with!(message, **options)
+    @signature_verification_failure_reason = { error: message }.merge(options)
     @signed_request_actor = nil
   end
 
@@ -209,8 +209,8 @@ module SignatureVerification
       end
 
       expires_time = Time.at(signature_params['expires'].to_i).utc if signature_params['expires'].present?
-    rescue ArgumentError
-      return false
+    rescue ArgumentError => e
+      raise SignatureVerificationError, "Invalid Date header: #{e.message}"
     end
 
     expires_time ||= created_time + 5.minutes unless created_time.nil?

app/services/activitypub/fetch_remote_actor_service.rb

@@ -28,6 +28,7 @@ class ActivityPub::FetchRemoteActorService < BaseService
     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?
+    raise Error, "Actor #{uri} has no 'preferredUsername', which is a requirement for Mastodon compatibility" unless @json['preferredUsername'].present?
 
     @uri      = @json['id']
     @username = @json['preferredUsername']

spec/controllers/concerns/signature_verification_spec.rb

@@ -16,6 +16,8 @@ describe ApplicationController, type: :controller do
   controller do
     include SignatureVerification
 
+    before_action :require_actor_signature!, only: [:signature_required]
+
     def success
       head 200
     end
@@ -23,10 +25,17 @@ describe ApplicationController, type: :controller do
     def alternative_success
       head 200
     end
+
+    def signature_required
+      head 200
+    end
   end
 
   before do
-    routes.draw { match via: [:get, :post], 'success' => 'anonymous#success' }
+    routes.draw do
+      match via: [:get, :post], 'success' => 'anonymous#success'
+      match via: [:get, :post], 'signature_required' => 'anonymous#signature_required'
+    end
   end
 
   context 'without signature header' do
@@ -118,6 +127,37 @@ describe ApplicationController, type: :controller do
       end
     end
 
+    context 'with request with unparseable Date header' do
+      before do
+        get :success
+
+        fake_request = Request.new(:get, request.url)
+        fake_request.add_headers({ 'Date' => 'wrong date' })
+        fake_request.on_behalf_of(author)
+
+        request.headers.merge!(fake_request.headers)
+      end
+
+      describe '#signed_request?' do
+        it 'returns true' do
+          expect(controller.signed_request?).to be true
+        end
+      end
+
+      describe '#signed_request_account' do
+        it 'returns nil' do
+          expect(controller.signed_request_account).to be_nil
+        end
+      end
+
+      describe '#signature_verification_failure_reason' do
+        it 'contains an error description' do
+          controller.signed_request_account
+          expect(controller.signature_verification_failure_reason[:error]).to eq 'Invalid Date header: not RFC 2616 compliant date: "wrong date"'
+        end
+      end
+    end
+
     context 'with request older than a day' do
       before do
         get :success
@@ -140,6 +180,13 @@ describe ApplicationController, type: :controller do
           expect(controller.signed_request_account).to be_nil
         end
       end
+
+      describe '#signature_verification_failure_reason' do
+        it 'contains an error description' do
+          controller.signed_request_account
+          expect(controller.signature_verification_failure_reason[:error]).to eq 'Signed request date outside acceptable time window'
+        end
+      end
     end
 
     context 'with inaccessible key' do
@@ -171,6 +218,7 @@ describe ApplicationController, type: :controller do
 
     context 'with body' do
       before do
+        allow(controller).to receive(:actor_refresh_key!).and_return(author)
         post :success, body: 'Hello world'
 
         fake_request = Request.new(:post, request.url, body: 'Hello world')
@@ -189,22 +237,67 @@ describe ApplicationController, type: :controller do
         it 'returns an account' do
           expect(controller.signed_request_account).to eq author
         end
+      end
 
-        it 'returns nil when path does not match' do
+      context 'when path does not match' do
+        before do
           request.path = '/alternative-path'
-          expect(controller.signed_request_account).to be_nil
         end
 
-        it 'returns nil when method does not match' do
+        describe '#signed_request_account' do
+          it 'returns nil' do
+            expect(controller.signed_request_account).to be_nil
+          end
+        end
+
+        describe '#signature_verification_failure_reason' do
+          it 'contains an error description' do
+            controller.signed_request_account
+            expect(controller.signature_verification_failure_reason[:error]).to include('using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)')
+            expect(controller.signature_verification_failure_reason[:signed_string]).to include("(request-target): post /alternative-path\n")
+          end
+        end
+      end
+
+      context 'when method does not match' do
+        before do
           get :success
-          expect(controller.signed_request_account).to be_nil
         end
 
-        it 'returns nil when body has been tampered' do
+        describe '#signed_request_account' do
+          it 'returns nil' do
+            expect(controller.signed_request_account).to be_nil
+          end
+        end
+      end
+
+      context 'when body has been tampered' do
+        before do
           post :success, body: 'doo doo doo'
+        end
+
+        describe '#signed_request_account' do
+          it 'returns nil when body has been tampered' do
             expect(controller.signed_request_account).to be_nil
           end
         end
       end
     end
   end
+
+  context 'when a signature is required' do
+    before do
+      get :signature_required
+    end
+
+    context 'without signature header' do
+      it 'returns HTTP 401' do
+        expect(response).to have_http_status(401)
+      end
+
+      it 'returns an error' do
+        expect(Oj.load(response.body)['error']).to eq 'Request not signed'
+      end
+    end
+  end
+end