Extbase in middlewares 

Middlewares inspect and modify the request and response: adding headers, short-circuiting with a redirect, answering a route directly. Extensions sometimes want domain data at that point like an API endpoint or a conditional redirect based on a record.

Whether Extbase can provide it depends entirely on where in the chain the middleware runs.

The essentials:

• The site, the language and the frontend TypoScript configuration are established by the frontend middleware chain. A middleware running before that point has none of them, and Extbase cannot resolve its configuration.
• A middleware running after the frontend has been prepared has all of it. The resolved site and language are available as request attributes, and can be tested for rather than assumed.
• A middleware ordered without constraints may run anywhere in the chain, so one that depends on the frontend having been prepared has to say so in its registration.
• Needing to establish a context before Extbase works is a sign the work may belong elsewhere: in a plugin behind a route enhancer, in a service called from a controller, or expressed directly against the database API.