How to Implement Auth and Route Protection Using Next.js Middleware

Next.js middleware runs at the network edge before every matched request, making it an efficient layer for authentication checks and route protection without hitting a database. Because edge runtime lacks full Node.js API support, JWT verification must use the 'jose' library instead of the standard 'jsonwebtoken' package. The middleware reads auth tokens from cookies, verifies them cryptographically, and either redirects unauthenticated users to a login page or passes user context downstream via request headers. A matcher configuration is essential to limit middleware execution to protected routes, avoiding unnecessary overhead on static assets. The pattern also handles edge cases such as expired tokens, stale cookie cleanup, and redirecting already-authenticated users away from login or signup pages.