Laravel 10: middlewareAliases, routeMiddleware & middlewareGroups

In new Laravel applications, the $routeMiddleware property of the App\Http\Kernel class has been renamed to $middlewareAliases to better reflect its purpose. Here’s how you should understand and work with these arrays:

1. $middlewareAliases (new in Laravel 10.x):
   • This array is introduced in Laravel 10.x to give a more intuitive name that reflects its purpose. When you create a new middleware, you can register it here with an alias, and then you can use that alias when specifying middleware in your routes.
   • For example, if you create a CheckUserStatus middleware, you might register it in $middlewareAliases with the ‘user.status’ alias. You’d then use this alias to attach the middleware to specific routes: Route::get('/dashboard', 'DashboardController')->middleware('user.status');
2. $routeMiddleware (from Laravel 9.x and earlier):
   • Despite the introduction of $middlewareAliases, it seems Laravel 10.x maintains compatibility with the $routeMiddleware property from earlier versions. This decision is likely for backward compatibility, allowing easier upgrades from previous versions without breaking existing middleware registrations.
   • You can still register your middleware here with an alias, exactly as you would in the $middlewareAliases array, and it will work as expected. However, since $middlewareAliases is the new standard going forward, it might be best to use that array for new middleware to keep up with the latest practices.
3. $middlewareGroups:
   • This array remains consistent between Laravel 9.x and 10.x. It’s used for defining groups of middleware that should be applied together to routes or route groups. Common groups are ‘web’ and ‘api’, each applying a stack of middleware appropriate for different types of HTTP requests (stateful web interactions versus stateless API calls, for example).

Given that both $routeMiddleware and $middlewareAliases are operational, you have some flexibility. For maintaining modern standards and forward compatibility, it’s advisable to use $middlewareAliases for registering new middleware.