先检查app/Http/Middleware/ 下是否有EnableCrossRequestMiddleware.php 这个文件，没有此文件使用此命令创建

php artisan make:middleware EnableCrossRequestMiddleware

然后修改EnableCrossRequestMiddleware.php 的handle

     /**
 * Handle an incoming request.
 *
 * @param  \Illuminate\Http\Request  $request
 * @param  \Closure  $next
 * @return mixed
 */
public function handle($request, Closure $next)
{
    $response = $next($request);
    $origin = $request->server('HTTP_ORIGIN') ? $request->server('HTTP_ORIGIN') : '';
    $allow_origin = [
        'http://127.0.0.1:8080',//允许访问
    ];
    if (in_array($origin, $allow_origin)) {
        $response->header('Access-Control-Allow-Origin', $origin);
        $response->header('Access-Control-Allow-Headers', 'Origin, Content-Type, Cookie, X-CSRF-TOKEN, Accept, Authorization, X-XSRF-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;
}

然后找到app/Http/Kernel.php文件中的 protected $middleware

    protected $middleware = [
    \App\Http\Middleware\CheckForMaintenanceMode::class,
    \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,
    \App\Http\Middleware\TrimStrings::class,
    \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,
    \App\Http\Middleware\TrustProxies::class,
    \App\Http\Middleware\EnableCrossRequestMiddleware::class,//新增跨域中间件
];