Use orm metamodel when querying DB.

[lealceldeiro]

Is your feature request related to a problem? Please describe.

In classes such as PostgreSQLBAuthorizationDAO, when querying the DB, the arguments for the entity field names are being hardcoded, i.e.: eUsername.

Describe the solution you'd like

This should be handled, for example, using an entity metamodel.

Additional context

Some quick info can be found around there, see https://stackoverflow.com/questions/3037593/how-to-generate-the-jpa-entity-metamodel and https://www.baeldung.com/hibernate-criteria-queries-metamodel