The Rabble user bundle adds user and permission management to Rabble, as well as a way to login to the admin panel. It is generally a good idea to install this bundle when using Rabble, unless you want to create your own user bundle.
Install the bundle by running
composer require rabble/user-bundleAdd the following class to your config/bundles.php file:
return [
...
Rabble\UserBundle\RabbleUserBundle::class => ['all' => true],
]