I think you are missing the point Andrzej, my pgadmin and postgresql do run on the same server and there is no need to open up port 5432 externally or even internally and block access to the external world via the firewall as pgadmin is connected via the local socket. And I like to keep it that way hence my question :)
...but ... I like to give members that do have a pgadmin account the possibility to use their account to be able to connect via an external program like qgis.
I like the maintenance to be as limited as possible so definitely not maintaining access via the pg_hda.conf or fiddling around with firewall regex rules for each user while they already have an pgadmin account.
As I do not like to open-up my postgresql port to the outside world and managing users via pgadmin is very user friendly. I was wondering if somehow it would be possible to give external applications like Qgis for instance access to the database via pgadmin?
For example in qgis in order to access the database it needs to connect directly to the postgresql port and I have to create a linux user for them. I do not want that. I rather manage this inside pgadmin. If qgis would somehow be able to connect to the db via a pgadmin api that would be really great.