In case you're somewhere where you can't login easily. Here is a response sample of the Wireless Clients Details API. As you can see it can feed back quite a bit of data. I'd test this out to see if "username" feeds you what you're looking for.
{
"macaddr": "c8:b5:ad:c3:b2:04",
"name": "name",
"ip_address": "10.29.31.251",
"username": "user",
"associated_device": "CB29870987",
"encryption_method": "UNKNOWN",
"usage": "28199089",
"health": "0",
"group_name": "dual_5GHz",
"swarm_id": "1523bca0014e94ed844d7dbde138b556993207f71af39d19df",
"network": "5Gz_0_1",
"user_role": "admin",
"manufacturer": "HTC Corporation",
"os_type": "Linux",
"connection": "Wired",
"speed": "444",
"maxspeed": "10000",
"signal_strength": "55",
"signal_db": "12",
"snr": "123",
"channel": "33e",
"band": "5 Ghz",
"labels": "[]",
"site": "null",
"radio_mac": "c8:b5:ad:c3:b2:04",
"vlan": "3333",
"radio_number": "1"
}