Deprecation: #83853 - Backend AjaxRequestHandler 

See forge#83853

Description 

The class \TYPO3\CMS\Backend\Http\AjaxRequestHandler has been marked as deprecated and will be removed in TYPO3 v10. This functionality has been moved into the backend's generic Request Handler functionality.

The AJAX functionality itself is not deprecated and can be used as before.

Impact 

Installations that use \TYPO3\CMS\Backend\Http\AjaxRequestHandler will trigger a deprecation warning.

Affected Installations 

All installations that use custom extensions that add classes derived from \TYPO3\CMS\Backend\Http\AjaxRequestHandler.

Migration 

Use a PSR-15 middleware for the Backend Middleware Stack or extend from the generic \TYPO3\CMS\Backend\Http\RequestHandler instead.