How to set up a database for authenticate and data management

Question

I just finished the in deph course of vaadin fusion (@marcushellberg). It was really good.

Now Im trying to do the same but now I have a Postgres database with info, but I don't know how to load the information in the grid from the database

And how to authenticate an user from database instead of hardcode the credentials... Anyone can help?

I just created my personalized entities, endpoints, repositories and the view for one of them however the view do not load the info from database, also I have the application.properties file with database info and tested

Is there something that I am missing?

Thanks in advance and if you need more info from my project just let me know.

I notice that in my browser I am getting this

Error: Endpoint 'SupermercadosEndpoint' method 'getSupermercadosData' request cannot be accessed, reason: 'Access denied'