Hi, Benjamin.
That depends on what do you mean by "Basic LDAP authentication for external apps". You can use LDAP bind against some external LDAP server as authentication method for Gluu Server itself, but it seems like you are talking about opening Gluu Server's own LDAP server for external apps to use for authetication. Gluu Server wasn't really designed for the latter, it's mostly used with apps that rely on web browser and HTTP protocol to handle authentication, and everything built upon this (protocols like SAML and OIDC).
You could make its internal LDAP server to listen on external ports, but that would just mean 95% of Gluu's capabilities are not used, if this will be its main purpose.