Assuming it is a Javascript based web-app, I strongly recommend using solid-auth-client.js and rdflib.js as mentioned in the “Make an app in your lunch break”-tutorial https://solid.inrupt.com/docs/app-on-your-lunch-break and https://solid.inrupt.com/docs/manipulating-ld-with-rdflib. Those libraries take care of all the heavy lifting needed for authentication and working with linked data.
You can see my “learning story” here: My first app - adding resources? - and a similar story here Question about retrieving data