How to sync deviceId with chrome-extension and .domain.com?

Hello,
I've developed a Chrome extension, and I have two websites under the domain .mycompany.com. I'm looking for a straightforward method to share the same deviceId between the Chrome extension and my two websites. The first website is located at mycompany.com, and the second one is at app.mycompany.com. Is there a convenient way to accomplish this?