With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fnUserLocalName
fn User Local Name
1.3.6.1.4.1.12356.3.1.1.2
Local firewall user name
Back to FORTINET-MIB MIB page.
IPHost Network monitor allows you to monitor fnUserLocalName on Fortinet device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Fortinet access points right now.