request 里怎么验证提交的验证码？

控制器里生成了个 '1234' 这样的验证码, 存到了session里 $request->session()->put('code', '1234),
前台提交了一个用户输入的验证码, 我想在request里实现验证，该怎么写？

下面是我的request.php

namespace App\Http\Requests;

use App\Http\Requests\Request;

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

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'mobile' => 'sometimes|required|mobile',
            'password' => 'sometimes|required|confirmed'
        ];
    }

    /**
     * 自定义错误信息
     *
     * @see \Illuminate\Foundation\Http\FormRequest::messages()
     */
    public function messages()
    {
        return [
            'mobile.required' => '请填写手机号',
            'mobile.mobile' => '手机格式有误',
            'password.required' => '请填写密码',
            'password.confirmed' => '两次密码不一致,请重试'
        ];
    }
}