Gluu requires oxd @ US$0.33/day?

I am implementing Nextcloud for a Linux User Group on a donated VPS. A number of other services are likely to be installed as well, such as gnu social and xmpp. It seems appropriate to try and have all such services work off the same user base. The group is entirely free, donation / volunteer run. We don’t even have a bank account.

I see the Gluu add-on and offer to install the open source server. e.g., - “If you don’t already have an OP you can deploy the free open source Gluu Server.”

However, at I see “Requirements - In order to use the NextCloud APP you will need a standard OP (like Google or a Gluu Server) and the oxd server.”

Is there an out of pocket expense to using Gluu with Nextcloud? Gluu appears open source / freely downloadable, oxd however appears to have a cost.

If so, I also see (And Gluu also serves SAML, and Shibboleth, for that matter, no mention of oxd to that point.) Apparently ApacheDS serves Kerberos, even.

This is all new to me - where to start in trying to set up a common user base across multiple apps, including Nextcloud. (Debian Jessie / OpenVZ VPS.) There can be no additional actual monetary cost involved.

Thanks for any thoughts.