Backend Routing

Each request to the backend is eventually executed by a controller. A list of routes is defined which maps a given request to a controller and an action.

Routes are defined inside extensions, in file Configuration/Backend/Routes.php for general requests and in Configuration/Backend/AjaxRoutes.php for AJAX calls.

Here is an extract of typo3/sysext/backend/Configuration/Backend/Routes.php:

use TYPO3\CMS\Backend\Controller;

 * Definitions for routes provided by EXT:backend
 * Contains all "regular" routes for entry points
 * Please note that this setup is preliminary until all core use-cases are set up here.
 * Especially some more properties regarding modules will be added until TYPO3 CMS 7 LTS, and might change.
 * Currently the "access" property is only used so no token creation + validation is made,
 * but will be extended further.
return [
        // Login screen of the TYPO3 Backend
        'login' => [
                'path' => '/login',
                'access' => 'public',
                'target' => Controller\LoginController::class . '::formAction',

        // Main backend rendering setup (previously called backend.php) for the TYPO3 Backend
        'main' => [
                'path' => '/main',
                'target' => Controller\BackendController::class . '::mainAction',
        // ...

So a routes file essentially returns an array containing routes mapping. A route is defined by a key, a path and a target. The "public" access property indicates that no authentication is required for that action.

More Information

Please refer to the following external resources and look at how the TYPO3 source code handles backend routing in your TYPO3 version.