Capturing traffic from specific client

[alexlev2004]

Hello,
I am implementing a remote access server where traffic of each client connecting to OpenVPN need to be captured separately as well each one has his own iptables rule set (INPUT/FORWARD chain).
I could not figure out how to use tcpdump/iptables filters for this case, as there can be multiple clients connecting via single tun interface, and it is not enough to filter by client source IP.
Probably possible to do with MAC address, or manage multiple openvpn servers but is there a better way ?
Thanks a lot,
Alex