Login to my app via smartsheet sso

I create a application with GUI to handle with data from smartsheet (crud). Then I make login module via OAuth2 flow to get the token to authentication and call some smartsheet API. But when I am done these procedures, I got a access token and refresh token which is not in jwt token. I use that token to call smartsheet API OK but how can I use that token for authenticate user from my application (because it is not jwt token and cannot decode any information from that token)? Do I need id_token for authenticating and how can it get it from smartsheet server?

Please give me some advise for this