Where should I save read and write key on node.js

Hi 🙂
Im trying to make Oauth signin on google. and got some questions!

on this documentation server should generate read and write secrets and pass it to the plugin UI. Where should I save these keys on node.js?

I thought I could save them on cookie. but realized that we couldnt use cookie on plug in…
database? or what else?

Thanks 🙂