Server A requests the interface of server B, so cross-domain problems generally arise.

XMLHttpRequest cannot load http://api.console.vms3.com/api/user. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' istherefore not allowed access.

This means that the server response does not allow cross-domain access.

Then we need to have the server support cross-domain access, which is added to the response header

'Access-Control-Allow-Origin: *'

Step 1: Create Middleware

Establish `app/Http/Middleware/AccessControlAllowOrigin.php` middleware hold 'Access-Control-Allow-Origin: *' Write to the head.
app/Http/Middleware/AccessControlAllowOrigin.php
<?php

namespace App\Http\Middleware;

use Closure;
use Illuminate\Support\Facades\Auth;

class AccessControlAllowOrigin
{
    /**
     *
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        header('Access-Control-Allow-Origin: *');
        header("Access-Control-Allow-Credentials: true");
        header("Access-Control-Allow-Methods: *");
        header("Access-Control-Allow-Headers: Content-Type,Access-Token");
        header("Access-Control-Expose-Headers: *");

        return $next($request);
    }

}

Step 2: Register Routing

Register this middleware into the kernel.
In protected $middleware array and protected $routeMiddleware array, respectively
Add the class name of the file we just created, using the alias cors.

Step 3: Setting up middleware protection interface

Then add its alias to the array of $middleware Groups ['api'], which is set to protect the api. In this article,'cors'
app/Http/Kernel.php

<?php

namespace App\Http;

use Illuminate\Foundation\Http\Kernel as HttpKernel;

class Kernel extends HttpKernel
{
    /**
     * The application's global HTTP middleware stack.
     *
     * These middleware are run during every request to your application.
     *
     * @var array
     */
    protected $middleware = [
        \Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,
        \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,
        \App\Http\Middleware\TrimStrings::class,
        \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,
        \App\Http\Middleware\AccessControlAllowOrigin::class,
    ];

    /**
     * The application's route middleware groups.
     *
     * @var array
     */
    protected $middlewareGroups = [
        'web' => [
            \App\Http\Middleware\EncryptCookies::class,
            \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
            \Illuminate\Session\Middleware\StartSession::class,
            // \Illuminate\Session\Middleware\AuthenticateSession::class,
            \Illuminate\View\Middleware\ShareErrorsFromSession::class,
            \App\Http\Middleware\VerifyCsrfToken::class,
            \Illuminate\Routing\Middleware\SubstituteBindings::class,
        ],

        'api' => [
            'throttle:60,1',
            'bindings',
            'cors'
        ],
    ];

    /**
     * The application's route middleware.
     *
     * These middleware may be assigned to groups or used individually.
     *
     * @var array
     */
    protected $routeMiddleware = [
        'auth' => \Illuminate\Auth\Middleware\Authenticate::class,
        'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
        'bindings' => \Illuminate\Routing\Middleware\SubstituteBindings::class,
        'can' => \Illuminate\Auth\Middleware\Authorize::class,
        'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
        'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
        'cors' => \App\Http\Middleware\AccessControlAllowOrigin::class,
    ];
}

Step 4: Adding routing to routing

Route::middleware('cors')->group(function () {
    //
});