The authorization code is one time use, so you shouldn’t be storing it at all but instead using it immediately when the user redirects to your backend.
Once your server exchanges the code it’ll get not just an Access Token, but a Refresh Token too, both of which should be stored so that the access token can be used for any API requests, and the refresh token used to generate a new access token and refresh token pair when the current token expires https://dev.twitch.tv/docs/authentication#refreshing-access-tokens
As long as the user hasn’t disconnect their Twitch account from your app, you’ll be able to use the refresh process whenever you need new tokens and not need the user to go through the process again.