Address review: cover DiskController#update in tests

Add integration coverage for the disk service PUT now that the initializer
relies on it being both session-gated and CSRF-exempt:

- unauthenticated PUT -> redirected to login (write blocked)
- authenticated PUT with forgery protection enabled and no authenticity
  token -> 204 (proves the signed-token service PUT stays CSRF-exempt and
  guards against the concern's protect_from_forgery re-arming it)

test/controllers/active_storage/direct_uploads_controller_test.rb

@@ -34,10 +34,46 @@ class ActiveStorage::DirectUploadsControllerTest < ActionDispatch::IntegrationTe
     assert_response :success
   end
 
+  test "disk update requires authentication" do
+    put direct_upload_url_for("hello"), params: "hello", headers: { "Content-Type" => "text/plain" }
+
+    assert_redirected_to new_session_url
+  end
+
+  test "disk update stores bytes for an authenticated session without a CSRF token" do
+    sign_in :david
+    url = direct_upload_url_for("hello")
+
+    # Forgery protection is off in test by default; turn it on so this proves the
+    # signed-token service PUT stays CSRF-exempt even when the concern re-arms it.
+    with_forgery_protection do
+      put url, params: "hello", headers: { "Content-Type" => "text/plain" }
+    end
+
+    assert_response :no_content
+  end
+
   private
     def blob_params
       content = "hello"
       { filename: "hello.txt", byte_size: content.bytesize, content_type: "text/plain", \
         checksum: Digest::MD5.base64digest(content) }
     end
+
+    def direct_upload_url_for(content)
+      blob = ActiveStorage::Blob.create_before_direct_upload! \
+        filename: "hello.txt", byte_size: content.bytesize, \
+        checksum: Digest::MD5.base64digest(content), content_type: "text/plain"
+      ActiveStorage::Current.set(url_options: { host: "once.campfire.test", protocol: "http" }) do
+        blob.service_url_for_direct_upload
+      end
+    end
+
+    def with_forgery_protection
+      original = ActionController::Base.allow_forgery_protection
+      ActionController::Base.allow_forgery_protection = true
+      yield
+    ensure
+      ActionController::Base.allow_forgery_protection = original
+    end
 end