対応したときのソース

app\Http\Middleware\Authenticate.php
<?php

namespace App\Http\Middleware;

use Illuminate\Auth\Middleware\Authenticate as Middleware;
use Illuminate\Http\Request;
use Illuminate\Auth\AuthenticationException;
use Illuminate\Support\Facades\Auth;

class Authenticate extends Middleware
{    
    protected function unauthenticated($request, array $guards)
    {
        throw new AuthenticationException(
            'Unauthenticated.', $guards, $this->redirectToByGuards($request, $guards)
            );
    }

    /**
     * Get the path the user should be redirected to when they are not authenticated.
     */
    protected function redirectToByGuards($request, $guards) {
        if (!$request->expectsJson()) {
            foreach ($guards as $guard) {
                if ($guard === 'admin') {
                    // guardごとに設定
                    return route('admin.login');
                } else {
                    // 初期設定と同じ
                    return route('login');
                }
            }
        }
    }
}
参考サイト
