Develop a "dummies guide" for Debian user apps to have full access to PostgreSQL

Hi. Background… We have a Java application that uses PostgreSQL to access several DBs. Currently all customers use Windows, so our whole dev and distribution is based on Windows. This works perfectly for us. These Java apps are typically on localhost, but may be elsewhere on the LAN. My current task is to port our application (Java & PostgreSQL) to Debian. - Currently I am using VirtualBox 5.2.12 and can run Debian 9, and PostgreSQL 10. - As a normal Debian user I can access everything I want using pgAdmin 3. - However, our Java app can't access any database. I have spent too many hours trialing, following tutorials, asking on the user groups etc, but I do not have the Linux/Debian or PostgreSQL admin skills to get this going with the appropriate logins, usernames, passwords, roles, permissions etc. Your task is to develop a canonical procedure (ie "a dummies guide") with every required baby step that assumes no Debian, Linux or Postgres pre-knowledge. - the outcome is a detailed step-by-step procedure - when I follow your procedure then my java application (not pgAdmin3 or psql etc) using only a username ("pguser") and password ("pguserpwd") has full access rights to the PostgreSQL server so that it can create, drop, read write to any database on that server. - start with a fresh Debian installation (probably 9 stretch) - create a Debian user "debuser" with password "debpwd" - install PG (presumably 10?) - make all required changes to postgres users, roles, [login to view URL], [login to view URL] etc - work from local host or any specified IP - it must use "out-of-the-box" Debian tools & commands etc - I would like you to do this in VirtualBox, so you can also advise how to install "virtualbox-guest-additions" onto the Debian guest (so I can get share folders working) The task is complete when I can follow your procedure like a robot and my app can access postgres exactly as it can now on Windows. My outcome is clear. The process to achieve that is negotiable. Thanks