This site is designed to show off NextJS 12's Middleware functionality.
It does this by simulating a product website. Products may be sold by multiple different sellers, and they may be marked as public or private. Using middleware, we can deliver really fast cached static responses to the public, while letting a seller view their page with the most up to date server-rendered information.
A full blog post detailing this can be found at topher.io/writing/next-middleware-private-pages.