External Auth: Roles and usergroups are not loaded properly with ldap backend

[sukhwinder33445]

Describe the bug

Roles and usergroups are not loaded properly when using external auth with ldap backend.

To Reproduce:

1. Create a user named user on ldap backend.
2. Create a usergroup named users on ldap backend and add user as a member.
3. Create a role named readOnly, assign only the users group to it, and grant general module access to monitoring and icingadb.
4. Ensure that the monitoring, icingadb, and cube (or graphite) modules are enabled.
5. Enable external authentication.
6. Log in using external authentication with the user account.

7. Open a `monitoring` dashboard pane.
   

Icinga Web 2 shows the following error:

NOTICE: PHP message: icingaweb2: ERROR - Can't get group memberships for user 'user' from backend 'auth_ldap'. An exception was thrown: Icinga\Exception\ConfigurationError in /icingaweb2/library/Icinga/Authentication/User/UserBackend.php:74 with message: User backends not set up. Please contact your Icinga Web administrator

ref/IP/62220

[sukhwinder33445]

Fixed in #5387.

[sukhwinder33445]

Unfortunately, I cannot reproduce this issue using the steps given in the description.