Windows


- download Windows client from this link: https://openvpn.net/community-downloads/
(direct URL  for Win10 client is: https://swupdate.openvpn.org/community/releases/openvpn-install-2.4.9-I601-Win10.exe )
- install client, clicking OK for all options proposed as default
- download ovpn-client.tar file from this link: https://tifpabox.tifpa.infn.it/index.php/s/uDF6tfsNG2EGD5w
- move tar file in C:/Program Files/OpenVPN/config and unpack it therein
- launch  OpenVPN program by clicking on the little icon with a locked screen found on the bottom bar of the desktop
- when asked username e password, give INFN-AAI credentials (provide only LDAP username, which, apart rare cases, corresponds to your surname).

MacOS


- download ovpn-client.tar file from this link: https://tifpabox.tifpa.infn.it/index.php/s/uDF6tfsNG2EGD5w
- click on tar file to unpack; directory ovpn-client containing configuration files will be created. Keep it open because needed later on.
- download the stable version of Tunnelblick program from this link: https://tunnelblick.net/downloads.html
- launch installation and move program in Applications directory
- launch program, it will ask if a configuration is available, answer no
- then  it will ask if you want to create a configuration, answer yes
- close windows that Tunnelblink has opened (both Textedit windows and Finder window)
- click on the little icon with a tunnel which appeared on the top bar, then click on VPN details
- a window will open with a white area on the left (under "Configurations")
- drag client.ovpn file (which is among files unpacked in the first step) and drop in such white area
- click on Connect button on bottom-right
- a new window appears to insert username and password wherein. Give INFN-AAI credentials (provide only LDAP username, which, apart rare cases, corresponds to your surname).

Linux


The procedure described below was tested on a Debian9 machine. It should apply to all kinds of Debian-derived systems (just replace the text in red below with the name of your distribution). It follows instructions provided at: https://community.openvpn.net/openvpn/wiki/OpenVPN3Linux, where the procedure for Red Hat-derived systems is also described.
- configure repository access and install VPN program by executing following commands in a root shell:

   # apt install apt-transport-https

   # wget https://swupdate.openvpn.net/repos/openvpn-repo-pkg-key.pub

   # apt-key add openvpn-repo-pkg-key.pub

   # wget -O /etc/apt/sources.list.d/openvpn3.list https://swupdate.openvpn.net/community/openvpn3/repos/openvpn3-stretch.list 

   # apt update

   # apt install openvpn3

- from now on you do not need root privileges anymore. As a normal user download ovpn-client.tar file from this link: https://tifpabox.tifpa.infn.it/index.php/s/uDF6tfsNG2EGD5w
- create ~/ovpn directory and unpack tar file therein
- to launch VPN client, execute the following command:

   $ openvpn3 session-start --config ~/ovpn/client.ovpn

- give INFN-AAI credentials (provide only LDAP username, which, apart rare cases, corresponds to your surname).
- to close VPN session, execute the following command:

   $ openvpn3 session-manage --config ~/ovpn/client.ovpn -D