https://www.collaboraoffice.com/code/ currently provides an nginx reverse proxy configuration. According to: https://github.com/nextcloud/richdocuments/issues/47 and the direct comment in: https://github.com/nextcloud/richdocuments/issues/47#issuecomment-304118374 this might be wrong and it should be considered to be replaced by the one in the second link which is also matching: https://icewind.nl/entry/collabora-online/
Fixed at https://www.collaboraoffice.com/code/