Backend is not required
First create your account / application and get your API credentials and configure your redirect uri : https://develop.battle.net/
Integration example ( Get access token and how to call Blizzard API )
import OAuth2BnetComponent from "oauth2-battle.net/src/battle.net/OAuth2Bnet.component";
// ...
// Integration example : https://github.com/sylvainSUPINTERNET/oauth2-battle.net/blob/master/src/App.tsx (get access token + request Blizzard API to get item detail)