anonaddy/app/Http/Requests/StoreAdditionalUsernameRequest.php

<?php

namespace App\Http\Requests;

use App\Rules\NotBlacklisted;
use App\Rules\NotDeletedUsername;
use Illuminate\Foundation\Http\FormRequest;

class StoreAdditionalUsernameRequest extends FormRequest
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'username' => [
                'required',
                'alpha_num',
                'max:20',
                'unique:users,username',
                'unique:additional_usernames,username',
                new NotBlacklisted,
                new NotDeletedUsername
            ],
        ];
    }
}