How do I go about using a token for later?

I am doing a OAuth flow for Shopify, after authentication the user is redirected to my site where I post and get a access token.But where I’m having trouble is say this user isn’t logged in my site yet or doesn’t have an account and needs to sign up, how can I save the authenticated access token for later when they do sign up or log in and I can save it under their account?

Submitted May 01, 2019 at 12:41AM by prgrmmr7