Fortigate 5.4 Explicit Proxy and Authentication

Hi Folks,

I would like to set up a Fortigate Firewall running 5.4.7 as an explicit proxy and have users authenticate by typing in their username and password. I want different A/D user groups to have different security profiles. So what I would like to do is just set up LDAP and use only LDAP authentication for the users. Can anyone tell me if this is possible? And if so which authentication method I should use in the proxy policy?

I could use FSSO but some devices are not on the domain, so I would rather just use LDAP credentials for the authentication. Any pointers appreciated.

Thanks, Moby.