2FAuth/app/Http/Controllers/Auth/RegisterController.php

<?php

namespace App\Http\Controllers\Auth;

use App\User;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\DB;
use App\Http\Controllers\Controller;
use Illuminate\Support\Facades\Hash;
use Illuminate\Auth\Events\Registered;
use Illuminate\Support\Facades\Validator;
use Illuminate\Foundation\Auth\RegistersUsers;

class RegisterController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Register Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles the registration of new users as well as their
    | validation and creation. By default this controller uses a trait to
    | provide this functionality without requiring any additional code.
    |
    */

    use RegistersUsers;
    
    /**
     * check if a user exists
     * @param  Request $request [description]
     * @return json
     */
    public function checkUser()
    {
        $user = DB::table('users')->first();

        return response()->json(['username' => isset($user->name) ? $user->name : null], 200);
    }

    /**
     * Handle a registration request for the application.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Illuminate\Http\JsonResponse
     */
    public function register(Request $request)
    {
        // check if a user already exists
        if( DB::table('users')->count() > 0 ) {
            // return response()->json(['message' => __('errors.already_one_user_registered')], 400);
            throw \Illuminate\Validation\ValidationException::withMessages(['taken' => __('errors.already_one_user_registered')]);
        }

        $this->validator($request->all())->validate();

        event(new Registered($user = $this->create($request->all())));

        //$this->guard()->login($user);

        return response()->json([
            'message' => 'account created',
            'token' => $user->createToken('MyApp')->accessToken,
            'name' => $user->name,
        ]);
    }


    /**
     * Create a new user instance after a valid registration.
     *
     * @param  array  $data
     * @return \App\User
     */
    protected function create(array $data)
    {
        return User::create([
            'name' => $data['name'],
            'email' => $data['email'],
            'password' => Hash::make($data['password']),
        ]);
    }
}