FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
This article explains how to use the diagnose wad user list command to view the number of explicit web proxy users, and diagnose wad user clear to de-authenticate users.

The CLI command "diagnose wad user list " will give the users authenticated using web proxy.

diagnose  wad user list
MWAGUIH         id:6990 VD: root, duration: 9699
RGHATTAS         id:6991 VD: root, duration: 9693
EMOSTAFA         id:6992 VD: root, duration: 9618
GYOUSRY         id:7010 VD: root, duration: 6531
MDIMITRY         id:7039 VD: root, duration: 2070
YZOUHAIR         id:7050 VD: root, duration: 480
MBADRA         id:7051 VD: root, duration: 251
HIBRAHIM         id:7052 VD: root, duration: 250
The command "diagnose wad user clear" can be used to clear current explicit proxy users.  Enter a user's id, IP and VDOM to clear this particular user, otherwise this clears all users.