Technical Tip: Configure Fortinet Single Sign On (FSSO) for SSL-VPN users via Syslog

aahmadzada · ‎11-08-2022

Description

This article describes the configuration steps necessary to apply FSSO rules to SSL VPN users.

Scope

FortiOS 7.0 and newer versions.

Solution

FSSO rules can be used for the traffic generated by remote access VPN users.

In order to have a proper and actual mapping of the username to the IP address that was assigned to the user by a FortiGate, the collector agent has to be aware of the IP address that was assigned to a given VPN user.

This can be done with RADIUS accounting messages. See the following document for an explanation:

Dynamic address support for SSL VPN policies.

However, the environment may not have a RADIUS server or cannot support a RADIUS server.

If this is the case, the user identity information can be delivered to the collector agent through Syslog.

A remote user group can be used for authentication while an FSSO group is separately used for authorization. Using a dummy policy for remote user authentication and a policy for FSSO group authorization, FSSO can be used with SSL VPN tunnels.

This image shows the authentication and authorization flow:

In this example, the Collector Agent is used as a syslog server. It gets syslog messages when the user connects to the VPN. By doing so, it gets the username and the actual IP Address that was received during the VPN connection queries the LDAP server for the group membership, and forms the FSSO entry, which later is sent to the FortiGate.

The user PC here is the PC with the IP address 192.168.180.99.

The Collector Agent is running on a dedicated server with IP address 192.168.100.203.

AD is running on a server with IP address 192.168.100.200.

AD is already configured with a group called sslvpn-users. The group sslvpn-users-fsso and user jsmith are members of these two groups.

Configure the Fortinet Single Sign-On Collector Agent.

Configure a password for FSSO:

Enable the Syslog Listener:

Configure the LDAP Server:

The LDAP server is necessary to configure the user group membership for the SSLVPN user.

Configure Syslog Rules:

MicrosoftTeams-image (16)1.png

Note:

Due to the nature of the FortiOS log message structure, the field 'Client IPv4 Field' must be configured as stated in the image with a space character at the end of the line:

tunnelip={{:client_ip}}

The remaining fields should not contain a space character at the end of the line:

Name: fsso-sslvpn-syslog

Trigger: logdesc=”SSL

Logon: 0101039947

Update: 0101039949

Logoff: 0101039948

Username Field: user=”{{:user}}”

Test the configured rule. If the rule is configured properly, the result will be as shown:

MicrosoftTeams-image (16).png

Map the configured rule to the FortiGate and LDAP:

Here, 192.168.100.1 is the IP address of the FortiGate.

Configure the FortiGate:

To configure the FortiGate in the CLI:

Set up the LDAP server:

config user ldap

edit "AD"

set server "192.168.100.200"

set cnid "samaccountname"

set dn "dc=test,dc=lab"

set type regular

set username "TEST\\Administrator"

set password admin_password

Setup FSSO connector:

config user fsso

    edit "FSSO_CA"

        set server "192.168.100.203"

        set password 123456

        set ldap-server "AD"

    next

end
Create a user group for the LDAP server:

config user group
edit "sslvpn_users"
set member "AD"
config match
edit 1
set server-name "AD"
set group-name "CN=sslvpn-users,CN=Users,DC=TEST,DC=LAB"
next
end
Create an FSSO user group:

config user group

    edit "sslvpn-users-fsso"

        set group-type fsso-service

        set member "CN=fsso_group1,CN=Users,DC=TEST,DC=LAB"

    next

end
Configure appropriate SSLVPN portal and authentication rules:

config vpn ssl web portal
edit "none"
next
edit "test_portal"
set tunnel-mode enable
set ip-pools "SSLVPN_TUNNEL_ADDR1"
next

config vpn ssl settings

    set servercert "Fortinet_Factory"

    set idle-timeout 0

    set tunnel-ip-pools "SSLVPN_TUNNEL_ADDR1"

    set tunnel-ipv6-pools "SSLVPN_TUNNEL_IPv6_ADDR1"

    set dns-server1 192.168.100.200

    set source-interface "port1"

    set source-address "all"

    set source-address6 "all"

    set default-portal "none"

config authentication-rule

        edit 1

            set groups "sslvpn_users"

            set portal "test_portal"

        next

    end

end
Configure firewall addresses:

config firewall address

    edit "none"

        set subnet 0.0.0.0 255.255.255.255

    next
Create one dummy policy for authentication only, and one regular FSSO policy for authorization:

config firewall policy

    edit 1

        set name "sslvpn-authentication-policy "

        set srcintf "ssl.root"

        set dstintf "port1"

        set action accept

        set srcaddr "all"

        set dstaddr "none"

        set schedule "always"

        set service "ALL"

        set groups "sslvpn_users"

    next

    edit 2

        set name " sslvpn-authorization-policy "

        set srcintf "ssl.root"

        set dstintf "port1"

        set action accept

        set srcaddr "all"

        set dstaddr "all"

        set schedule "always"

        set service "ALL"

        set groups "sslvpn-users-fsso"

    next

Configure Syslog logging: Only the specific syslog messages that are listed in the free-style log filter will be sent to the collector agent:

config log syslogd setting

set status enable

set server "192.168.100.203"

end

config log syslogd filter

set forward-traffic disable

set local-traffic disable

set multicast-traffic disable

set sniffer-traffic disable

set ztna-traffic disable

set anomaly disable

set voip disable

set gtp disable

config free-style

edit 1

set category event

set filter "((logid 0101039947) or (logid 0101039948) or (logid 0101039949))"

end

These log IDs contain the necessary information to create the FSSO entry:

Log ID	Log Description	Log Meaning
0101039947	LOG_ID_EVENT_SSL_VPN_SESSION_TUNNEL_UP	SSL VPN tunnel up
0101039948	LOG_ID_EVENT_SSL_VPN_SESSION_TUNNEL_DOWN	SSL VPN tunnel down
0101039949	LOG_ID_EVENT_SSL_VPN_SESSION_TUNNEL_STATS	SSL VPN statistics

Results:

get vpn ssl monitor

SSL-VPN Login Users:

Index User Group Auth Type Timeout Auth-Timeout From HTTP in/out HTTPS in/out Two-factor Auth

0 jsmith sslvpn_users 16(1) 28750 28750 192.168.180.99 0/0 0/0 0

SSL-VPN sessions:

Index User Group Source IP Duration I/O Bytes Tunnel/Dest IP

0 jsmith sslvpn_users 192.168.180.99 50 10819/0 10.212.134.200

diag firewall auth list

10.212.134.200, JSMITH

type: fsso, id: 0, duration: 12, idled: 12

server: FSSO_CA

packets: in 0 out 0, bytes: in 0 out 0

group_id: 3 33554433

group_name: sslvpn-users-fsso CN=fsso_group1,CN=Users,DC=TEST,DC=LAB

10.212.134.200, jsmith

type: fw, id: 0, duration: 13, idled: 13

expire: 28786, allow-idle: 28799

flag(80): sslvpn

server: AD

packets: in 0 out 0, bytes: in 0 out 0

group_id: 2

group_name: sslvpn_users

The first entry is the entry that came from the collector agent as an FSSO logon (type: fsso).

The second entry is the user authentication for the SSL VPN connection (type: fw, flag(80): sslvpn).