Limit access to collabora server?

Nextcloud is on nc.mydomain.com and Collabora on cb.mydomain.com. Everything works fine, but cb.mydomain.com does not seem protected in any way. How can I limit access to it so that only nc.mydomain.com can use the server at cb.mydomain.com?

Edit:
I found the answer. A whitelist of domains is set in /etc/coolwsd/coolwsd.xml

Documentation is here: https://sdk.collaboraonline.com/docs/installation/Configuration.html#backend-storage-configurations