You can use bind rules to indicate that a permission applies to anyone who has successfully bound to the directory. The all keyword therefore allows access by all authenticated users. This allows general access while preventing anonymous access.
For example, to grant read access to the entire tree to all authenticated users, create the following ACI on the dc=example,dc=com node:
aci: (version 3.0; acl "all-read"; allow (read) userdn="ldap:///all";)