discourse-ldap-auth | Discourse plugin to enable LDAP | Identity Management library

I currently try to configure Discourse to only allow users in a specific ldap group to log in. Discourse has a plugin called discourse-ldap auth ( https://github.com/jonmbake/discourse-ldap-auth ). This plugin uses the omniauth ldap module: https://github.com/omniauth/omniauth-ldap

My discourse plugin configuration (the configuration is actually used by the discourse plugin for the omniauth ldap module):

• ldap enabled: true
• ldap hostname: the hostname of my ldap server
• ldap port: 389
• ldap method: plain
• ldap base: the base of my ldap server
• ldap uid: userPrincipalName
• ldap bind dn: Nothing
• ldap password: Nothing
• ldap filter: (&(userPrincipalName=%{username})(memberOf=cn=[the name of the required group],ou=....,[base]))

When using this configuration, nobody can log in to the forum. When I use the bind dn and password, everybody can log in. I also tried this filter without success (copied from my ldap servers filter):

• (&(&(&(userPrincipalName=%{username})(memberOf=[dn of the group]))))

What do I have to configure, to only allow users in that specific group to log in?

I didn't found any errors or indicators in the log. Please help!

Thanks fou your help and attention!