There is no user provider for user "...". Shouldn't the "supportsClass()" method of your user provider return true for this classname?

Question

I've been using this Userprovider with Symfony, which extends the original LdapUserProvider and only adds some roles, depending on the ActiveDirectory groups the user is in. It was working fine, but since Symfony 4.4 Symfony\Component\Security\Core\User\LdapUserProvider is deprecated and Symfony\Component\Ldap\Security\LdapUserProvider should be used instead.

src/Security/LdapUserProvider.php

namespace App\Security;

use Symfony\Component\Ldap\Entry;
use Symfony\Component\Security\Core\User\LdapUserProvider as SymfonyLdapUserProvider;
#use Symfony\Component\Ldap\Security\LdapUserProvider as SymfonyLdapUserProvider;
use Symfony\Component\Security\Core\User\User;

class LdapUserProvider extends SymfonyLdapUserProvider
{
    private static $roles = [
        'ROLE_MANAGEMENT' => [
            'name' => 'Verwaltung',
            'groups' => [
                'CN=Verwaltung,OU=Personen,DC=example,DC=com',
            ],
        ],
        'ROLE_SC' => [
            'name' => 'IT',
            'groups' => [
                'CN=IT-MA,OU=Gruppen,DC=example,DC=com',
            ],
        ],
        'ROLE_DOMAINADMIN' => [
            'name' => 'Domain Admin',
            'groups' => [
                'CN=Domain Admins,CN=Users,DC=example,DC=com',
            ],
        ],
        // some more roles ...
    ];

    protected function loadUser($username, Entry $entry)
    {
        $roles = ['ROLE_USER'];
        if ($entry->hasAttribute('memberOf')) {
            $roles = array_merge($roles, $this->getRolesFromGroups($entry->getAttribute('memberOf')));
        }
        $dn = $entry->getAttribute('distinguishedName')[0];
        $elements = explode(',', $dn);
        $basePath = array_slice($elements, ($_ENV['ADLDAP_BASEDN_DEPTH']*-1));
        $_SESSION['currentUser']['baseDn'] = implode(',', $basePath);
        return new User($username, null, $roles);
    }

    private function getRolesFromGroups(array $userGroups)
    {
        $roles = [];
        foreach ($this::$roles as $key => $role) {
            foreach ($role['groups'] as $group) {
                if (in_array($group, $userGroups)) {
                    $roles[] = $key;
                    break;
                }
            }
        }
        return $roles;
    }

    public function supportsClass($class)
    {
        $test = User::class === $class || is_subclass_of($class, User::class);
        dump($test);
        return $test;
    }
}

However, when I replace Symfony\Component\Security\Core\User\LdapUserProvider with Symfony\Component\Ldap\Security\LdapUserProvider I get the following Exception:

There is no user provider for user "Symfony\Component\Security\Core\User\User". Shouldn't the "supportsClass()" method of your user provider return true for this classname?

The funny thing is: I tested the return value of function supportsClass($class) and it returns true.

I found some questions like this one:

• There is no user provider for user, symfony 3.4.37 and 4.4.3

but they deal with custom User entities, which I don't have. Can anybody give me a hint where this error is coming from, if not from my UserProvider?

Symfony is at version 4.4.29. Excerpts from other relevant files:

config/services.yaml

Symfony\Component\Ldap\Ldap:
    arguments: ['@Symfony\Component\Ldap\Adapter\ExtLdap\Adapter']
Symfony\Component\Ldap\Adapter\ExtLdap\Adapter:
    arguments:
        -   host: '%env(ADLDAP_HOST)%'
            port: '%env(ADLDAP_PORT)%'
            options:
                protocol_version: 3
                referrals: false

config/packages/security.yaml

security:
    providers:
        ad:
            ldap:
                service: Symfony\Component\Ldap\Ldap
                base_dn: '%env(ADLDAP_BASEDN)%'
                search_dn: '%env(ADLDAP_USERDN)%'
                search_password: '%env(ADLDAP_PASSWORD)%'
                default_roles: ROLE_USER
                uid_key: 'samaccountname'
                extra_fields: ['distinguishedName']
    firewalls:
        dev:
            pattern: ^/(_(profiler|wdt)|css|images|js)/
            security: false
        main:
            anonymous: ~
            form_login_ldap:
                service: Symfony\Component\Ldap\Ldap
                login_path: login
                check_path: login
                dn_string: '%env(ADLDAP_BASEDN)%'
                query_string: '(samaccountname={username})'
            logout:
                path: /logout
                target: login

    access_control:
        - { path: ^/login, roles: IS_AUTHENTICATED_ANONYMOUSLY }
        - { path: ^/, roles: ROLE_USER }