Aliasing Backend URL through Rewrite Rules

I’m trying to hide my backend URL (https://cfworker.username.workers.dev) by creating a rewrite URL (https://backend-alias). This is to prevent exposure of the original URL, but Cloudflare Pages can’t call the new URL during build. My rewrite setup uses a custom filter expression with ‘starts with’ operator for https://backend-alias, and rewrites the path to the original URL, preserving the query.