How `hibernate.connection` properties are handled actually depends on the ConnectionProvider.  The DriverManagerConnectionProvider is the main consumer of them, and it just passes them through to opening the Connection.

Other ConnectionProviders do use the "main" hibernate.connection properties like user and pass.  DataSources for example can be secured.  So we pass them to the javax.sql.DataSource#getConnection(java.lang.String, java.lang.String) call.