Authentication token instead of username / password

Question

I'm trying to build an app with instagram api. I created a authentication screen which is going webview and letting user to log in. When user login ,authorization gives me a token. But can i use this token instead of username/password ? Because im using same scrap data like instaloader, private apis. etc. But all of this need username and password. No one will enter their instagram to unknown 3rd party application. So i have to do it with authentication. How can i use my auth token instead of username and password in python , javascript etc. All i need to learn that information. Or how can i transfer session for that "this user logged" in ?

(Note : im building this app in flutter/dart)