admin/app/Http/Middleware/AdminAuthenticate.php

<?php

namespace App\Http\Middleware;


use Closure;
use Illuminate\Auth\AuthenticationException;
use Illuminate\Auth\Middleware\Authenticate;
use Illuminate\Support\Facades\Auth;

//use Illuminate\Contracts\Auth\Factory as Auth;



class AdminAuthenticate
{
    /**
     * The authentication factory instance.
     *
     * @var \Illuminate\Contracts\Auth\Factory
     */
    protected $auth;

    /**
     * Create a new middleware instance.
     *
     * @param  \Illuminate\Contracts\Auth\Factory  $auth
     * @return void
     */
    public function __construct(Auth $auth)
    {
        $this->auth = $auth;
    }

    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @param  string[]  ...$guards
     * @return mixed
     *
     * @throws \Illuminate\Auth\AuthenticationException
     */
    public function handle($request, Closure $next, ...$guards)
    {
        if (!Auth::guard('admin')->check()) {
            return redirect('/admin/login');
        }

        return $next($request);
    }

}