Using Universal Login with an express.js app

I really don’t know how to properly articulate my question so i’ll error on the side of providing to much information.

My webapp is using the BFF (Backend for Frontend) architectural pattern in which an express.js app handles REST api requests with any path starting with /api and any other path a React SPA is delivered. That being said my local dev setup requires both the express app and React app to be running, so I have the express app listening on port 8000, and the React app is listening on port 3000. When a user accesses the path localhost:3000/api/ready they request would be proxied over to the express app and that works great.

I’d like to use Universal Login with this setup but i’m not sure I’m able to. In my local environment I can’t use the express-openid-connect because then my FE is unaware of Auth, but I also can’t use auth0-react to implement authentication in my SPA because I’d have to inject the Auth0 Domain, and Client ID at build time and my build system cannot support that.

Curious if there’s any idea’s on how I can resolve any of this. I know it’s super generic but I really don’t even know where to start with this. I’ve read through dozens of quickstarts and dozens of pages of docs but nothing actually teaches me what is going on so don’t feel like I really know anything about Auth0 to ask an intelligent question.