A PoC tracker that uses cookie keys instead of values.
To simulate multiple domains, edit your hosts (C:/Windows/System32/drivers/etc/hosts or /etc/hosts) file (with admin/root) to include the following domains
127.0.0.1 a.test
127.0.0.1 b.test
127.0.0.1 c.test
You'll need to restart your browser in order to have those resolve.
Run npm install and then node index.js.
In one browser, visit https://a.test:3000/a and https://b.test:3000/b. Open those in another browser as well. Visit https://a.test:3000/history to view the tracked history.