I use Calibre authentication and SSL/ reverse proxy using NGINX.
calibre :
http://192.168.20.25:8181
https://books.mydomain.com => (Linuxserver/SWAG - docker)
I have Linuxserver/SWAG - docker as NGINX/LetsEncrypt docker which points to the Calibre docker.
I have around 6 users and its all working fine.
All the users have their own library folder in Calibre.