Documentation on multi domain sign in

We have a React app (CRA) where we need to run multiple subdomains.

For example:

signup.domain.com
system.domain.com

We are using Cognito, and have built our own signup/login components that uses `Auth` behind the scenes (we built these because the AWS built components at the time had some limitations).

I'm struggling to find documentation/examples on how to sign in a user across all subdomains. I've seen `cookieStorage` mentioned, but I am unsure how to implement it exactly and there seems to be no documentation on how to use this.

Has anyone done this? Any code examples?

Specifically, the user will be on signup.domain.com when signing up and we are then doing a login behind the scenes once the user has finished signing up and then redirect them to the system.domain.com and the wish here is to keep the user signed in, no matter what subdomain they are on.