Laravel中的跨域问题需要分两种情况。Laravel 7是一种方案，Laravel 7以下是一种方案。

Laravel 7及以上解决方案

Laravel 7及以上版本，可以使用Laravel框架自带的跨域处理机制。
默认带有 fruitcake/laravel-cors 开发包。并且会在app/Http/Kernel.php中的全局中间件中，自动引入跨域处理中间件\Fruitcake\Cors\HandleCors::class。

    protected $middleware = [
        \App\Http\Middleware\TrustProxies::class,
        \Fruitcake\Cors\HandleCors::class,
        \App\Http\Middleware\PreventRequestsDuringMaintenance::class,
        \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,
        \App\Http\Middleware\TrimStrings::class,
        \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,
    ];

我们只需要在config/cors.php文件中，根据自己的项目需求，修改相关配置即可。

<?php

return [

    /*
    |--------------------------------------------------------------------------
    | Cross-Origin Resource Sharing (CORS) Configuration
    |--------------------------------------------------------------------------
    |
    | Here you may configure your settings for cross-origin resource sharing
    | or "CORS". This determines what cross-origin operations may execute
    | in web browsers. You are free to adjust these settings as needed.
    |
    | To learn more: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
    |
    */

    'paths' => ['*'],

    'allowed_methods' => ['*'],

    'allowed_origins' => ['*'],

    'allowed_origins_patterns' => [],

    'allowed_headers' => ['*'],

    'exposed_headers' => [],

    'max_age' => 0,

    'supports_credentials' => false,

];

Laravel 7以下解决方案

Laravel 5和Laravel 6就需要我们自己来创建一个中间件来处理跨域问题。
中间件的代码为：

<?php
namespace App\Http\Middleware;
use Closure;
class EnableCrossRequestMiddleware{

    public function handle($request, Closure $next){
        $response = $next($request);

        $response->header('Access-Control-Allow-Origin', '*');
        $response->header('Access-Control-Allow-Headers', 'Origin, Content-Type, Cookie, X-CSRF-TOKEN, Accept, Authorization, X-XSRF-TOKEN,token');
        $response->header('Access-Control-Expose-Headers', 'Authorization, authenticated');
        $response->header('Access-Control-Allow-Methods', 'GET, POST, PATCH, PUT, OPTIONS');
        $response->header('Access-Control-Allow-Credentials', 'true');
        return $response;
    }
}

然后，我们可以将中间件定义到app/Http/Kernel.php文件中的路由中间件中，后面通过在路由中使用该中间件。

    protected $routeMiddleware = [
        'cross' => \App\Http\Middleware\EnableCrossRequestMiddleware::class, // 跨域
    ];