LDAP role in Symfony 4

I'm using the ldap component on my project in Symfony 4. It works great, authenticates successfully but the only role that I can set on users is the default_role provided in the option of the ldap provider in the security.yaml... All the doc I found wasn't very helpfull whether people use database to manage users or they don't talk about role when they're using the ldap component. Here is my security.yaml if needed :

security.yaml :

security:
# https://symfony.com/doc/current/security.html#where-do-users-come-from-user-providers
providers:
    #in_memory: { memory: null }

    my_ldap:
        ldap:
            service: Symfony\Component\Ldap\Ldap
            base_dn: 'my_base_dn'
            search_dn: 'my_search_dn'
            search_password: '%env(resolve:LDAP_PASSWORD)%'
            default_roles: ROLE_USER #rôle par défaut donnéà l'utilisateur authentifié

firewalls:
    dev:
        pattern: ^/(_(profiler|wdt)|css|images|js)/
        security: false
    main:
        anonymous: ~

        form_login_ldap:
            provider: my_ldap
            service: Symfony\Component\Ldap\Ldap
            dn_string: 'my_dn_string'
            query_string: '(&(sAMAccountName={username})(memberOf=CN=***))'
            login_path: login #route vers laquelle l'utilisateur sera redirigé si il tente d'accéder à une ressource protégé sans être authentifié
        #/!\/!\/!\ NE PAS METTRE EN COMMENTAIRE SINON SUPPRESSION DES LOGS D'ERREURS !! /!\/!\/!\
            check_path: login #route vers laquelle doit être envoyé la requête POST du formulaire
            always_use_default_target_path: true
            default_target_path: homePage #page vers laquelle l'utilisateur authentifié est redirigé

        logout:
                path: app_logout
                target: login
        # activate different ways to authenticate
        # https://symfony.com/doc/current/security.html#firewalls-authentication

        # https://symfony.com/doc/current/security/impersonating_user.html
        # switch_user: true

If anyone have a solution or an idea !!