Laravel 5 Add errors in an array using After Validation Hook

I'm trying to add a function in my app where users are allowed to change their account password. I have three fields and my view looks like this:

<form class="form" role="form" action="" method="post">
    

    <div class="form-group label-floating ">
        <label class="control-label" for="oldpassword">Old Password</label>
        <input type="password" name="oldpassword" class="form-control">

        @if ($errors->has('oldpassword'))
            <span class="help-block">
                <strong></strong>
            </span>
        @endif
    </div>

    <div class="form-group label-floating ">
        <label class="control-label" for="newpassword">New Password</label>
        <input type="password" name="newpassword" class="form-control">

        @if ($errors->has('newpassword'))
            <span class="help-block">
                <strong></strong>
            </span>
        @endif
    </div>

    <div class="form-group label-floating">
        <label class="control-label" for="newpassword_confirmation">Confirm Password</label>
        <input type="password" name="newpassword_confirmation" class="form-control">
    </div>

    <div class="form-group">
        <button class="btn btn-raised btn-primary">Change</button>
    </div>
</form>

Firstly, I want to check if all fields are completely filled up and for that I used Validator. And then check if the oldpassword is match from the database so I use if (Auth::attempt(array('password' => $request->oldpassword))) condition. I also found in the laravel 5.2 documentation the After Validation hook. I don't know what is wrong but it seems it don't validates the oldpassword field when I typed a wrong password.

My controller:

$validator = Validator::make($request->all(), [
    'oldpassword' => 'required|max:255',
    'newpassword' => 'required|min:6|max:255|confirmed',
    ]);
$validator->after(function($validator) use($request) {
    if (Auth::attempt(array('password' => $request->oldpassword))) {
        $validator->errors()->add('oldpassword', 'Old password dont match in our database.');
    }
});
if ($validator->fails()) {
    // Toastr
    $title = "Oops!";
    $message = "Please make sure to fill all required fields.";
    $options = [
        'progressBar' => false,
        'positionClass' => 'toast-top-right',
        'timeOut' => 6000,
    ];
    Toastr::error($message, $title, $options);
    return redirect()->back()
        ->withErrors($validator);
} else {
    return 'success'; // for testing only
}

Any idea regarding this?

via Chebli Mohamed