Connecting to Postgres and managing users on Bubble

I would like to know how bubble handles the database connections and manages users within.
I am building a multi tenant app which as

  1. Multiple customers
  2. One customer has multiple users

In my usecase I would like to connect the app to an external database which is Postgres. But I am stuck with a confusion on how bubble handles the users.

I have setup Postgres on AWS and created customer table and other tables related to customer.
Now how do I link the User table on bubble to the customer table on Postgres?

Or should I move the users also to Postgres? In that case I need to manage user credentials, security etc…
How hybrid querying works for example, show data of customer for that loggedin user?

Any help will be highly appreciated.