The current docs on the WLAN.scan() method indicates the following 5 authmode modes:

0 – open
1 – WEP
2 – WPA-PSK
3 – WPA2-PSK
4 – WPA/WPA2-PSK

I recently scanned for networks and found one with an authmode 5 which should correspond to a WIFI-AUTH/WPA2-ENTERPRISE authmode but the network authmode module constants available are:

AUTH_MAX (6)
AUTH_OPEN (0)
AUTH_WEP (1)
AUTH_WPA2_PSK (3)
AUTH_WPA_PSK (2)
AUTH_WPA_WPA2_PSK (4)