Shopify OAuth in Photoshop UXP Plugin – Is a Backend Required?

I’m integrating Shopify OAuth into a Photoshop UXP plugin and have a quick question.

Is a backend (Node.js/Express or similar) mandatory to handle the authorization code and exchange it for an access token?
Since the client secret must stay secure, can this flow be completed without a server?

Would appreciate clarification from anyone who has implemented this.