Using p12 certificates for VPN in Gnome NetworkManager

My employee uses p12 certifcates for OpenVPN. On Manjaro Linux, the
Network Manager does not support these directly, so I had to extract the
CA certificate, User certificate and private key to be able to configure
the VPN.

    $ openssl pkcs12 -in cert.p12 -out userca.pem -cacerts -nokeys
    $ openssl pkcs12 -in $pfx -out usercert.pem -clcerts -nokeys
    $ openssl pkcs12 -in $pfx -out userkey.pem -nocerts

For the userkey I also had to set a password and supply it to the ?User
key password? option in the Edit connection dialog.