Plex is vulnerable using port forward for remote access

[blim5001]

There is a similar thread here:

why can anyone can login with their username to my server even outside of my network?

I’ve searched extensively for this on google but I found no one who had a proper solution for this. Is this a feature for plex premium? why can anyone login with any account to my server and this is a fresh image with docer. Please provide a solution otherwise I can’t really use plex with out the least bit of security?