cd /home/username/openvpn
openssl pkcs12 -export -in AmahiHDAClientAmahi-Client-OpenVPN.crt -inkey AmahiHDAClientAmahi-Client-OpenVPN.key -certfile ca-cert.crt -name Amahi -out certs.p12
You will be asked for a export password for the certs.p12 file - enter amahi twice.