Laravel 5.2 how to use config::set in middleware

I want to use config::set in my Middleware for the set the value globally. But it is generating error.

Below is the code which I am using

public function handle($request, Closure $next, $guard = 'admin') {

        if (!Auth::guard($guard)->check()) {
            return redirect('/admin/login');
        }

        //dd(Auth::guard('admin')->user()->id);
        $admin = $this->admin->with('adminRole')->find(Auth::guard('admin')->user()->id);
        config::set('bmc.admin_permission', $admin);    

        // check user roles
        if (array_key_exists('0', $admin->adminRole) && isset($admin->adminRole[0]->name)) {
            dd($admin->hasRole($admin->adminRole[0]->name));
        }
        return $next($request);
    }

Here is the error which I get

Class 'App\Http\Middleware\config' not found

via Chebli Mohamed