FSSO not working for explicit web proxy

Hello,

this is my firs post here :)

We've a FortiGate 70D with FortiOS 5.2.3 (build 670) and I'm trying to implement explcit proxy with SSO in AD (Windows Server 2012R2).

The problem is that authentication is not working and browsers ask for user and password and even if insert them manually, it cannot authenticate.

Here are configurations done: