Describe middleware.js.
Middleware allows you to run code before a request is completed. Then, based on the incoming request, you can modify the response by rewriting, redirecting, modifying the request or response headers, or responding directly.
Use the file middleware.ts (or .js) in the root of your project to define Middleware. For example, at the same level as pages or app, or inside src if applicable.
While only one middleware.ts file is supported per project, you can still organize your middleware logic modularly. Break out middleware functionalities into separate .ts or .js files and import them into your main middleware.ts file.
matcher allows you to filter Middleware to run on specific paths.