laravel $request->input() doesn't work

I'm trying to retrieve a single input from laravel request $request->input('username') but it returns undefined in ajax response , I tried $request->only('username') as well as $request->username but no of them work , exept for $request->all() which returns the right data object : Object {username: "username", password: "password", _token: "uKi2r3G1XPiOLhi13da3NC67ssjc1qmeiGWFtQNM"} , so I need to access single values

via Chebli Mohamed