User authentication for Unity game embedded in Wordpress, hosted on Bluehost server

Hi, I’m developing my first game using Unity, and I want to use Mongodb for user data and authentication, but I’m new to all of this, and struggling to figure out the right setup for me. The game is multiplayer, online, and I have a Wordpress website setup using a Bluehost server. I want to embed my Unity game into my Wordpress website, and I’m trying to figure out where to put/what to do with the Mongodb Cluster. I know Mongo Atlas is commonly used for hosting clusters, but I’m wondering if it’s possible (and cost effective) to host the cluster on my Bluehost server. I’m also aware that Mongo Realm can make integration with Unity easier, but I honestly don’t really understand what Realm does and if it applies to my situation.

So far, I have been able to set up a local Mongodb Cluster and read/write relevant player data from Unity, but I have not set up capabilities for multiple users and authentication. As far as authentication goes I know basically nothing, and I’m not really sure how it fits into all of this. I would like to have a dedicated login screen on the embedded unity game, but I’m not sure how it would communicate with the Mongo cluster and what data needs to be read to authenticate.

I have tried watching the series “Game Development with MongoDB and Unity”, but in their project they use Mongodb Atlas and a Node.js server, and I’m not sure how things would work differently if I am using a cluster on a Bluehost server. If anyone can point me in the right direction it would be much appreciated!