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Configuring client certificate authentication on the LDAP server

Administrators can configure a FortiGate client certificate in the LDAP server configuration when the FortiGate connects to an LDAPS server that requires client certificate authentication.

config user ldap
    edit <ldap_server>
        set client-cert-auth {enable | disable}
        set client-cert <source>
    next
end

Example

In this example, the FortiGate is configured as an explicit web proxy. It connects to the Windows AD server through LDAPS, where the Windows server requires a client certificate to connect. The client certificate is configured in the CLI.

The endpoint PC connecting to the web server will first need to authenticate to the explicit web proxy before accessing the server.

While this example demonstrates an LDAP client certificate for an explicit proxy configuration, LDAP client certificates can be used in firewall authentication, transparent proxy, ZTNA, and where ever LDAP configurations are used on the FortiGate.

To configure a client certificate on the LDAP server:
  1. Enable the explicit web proxy on port2:

    config system interface
        edit "port2"
            set explicit-web-proxy enable
        next
    end
  2. Upload the client certificate to the FortiGate:

    config vpn certificate local
        edit "Zach"
            set password **********
            set private-key <private key>
            set certificate <certificate>
        next
    end
  3. Configure the LDAP server settings:

    config user ldap
        edit "ldaps"
            set server "172.16.200.57"
            set server-identity-check disable
            set cnid "CN"
            set dn "CN=Users,DC=ftnt,DC=com"
            set secure ldaps
            set port 636
            set client-cert-auth enable
            set client-cert "Zach"
        next
    end
  4. Configure the authentication scheme:

    config authentication scheme
        edit "1"
            set method basic
            set user-database "ldaps"
        next
    end
  5. Configure the authentication rule:

    config authentication rule
        edit "1"
            set srcintf "port2"
            set srcaddr "all"
            set dstaddr "all"
            set active-auth-method "1"
        next
    end
  6. Configure the user group:

    config user group
        edit "test"
            set member "ldaps"
        next
    end
  7. Configure the proxy policy with the user group:

    config firewall proxy-policy
        edit 1
            set proxy explicit-web
            set dstintf "port3"
            set srcaddr "all"
            set dstaddr "all"
            set service "webproxy"
            set action accept
            set schedule "always"
            set srcaddr6 "all"
            set dstaddr6 "all"
            set groups "test"
            set utm-status enable
            set ssl-ssh-profile "deep-inspection-clone"
            set av-profile "av"
        next
    end

Testing and verification

When traffic from the endpoint PC matches a policy and triggers authentication, the FortiGate starts the LDAPS TLS connection handshake with the Windows AD. The LDAPS server requests a client certificate to identify the FortiGate as a client. The FortiGate provides a configured client certificate, issued to zach.com, to the LDAPS server.

The following communication between the FortiGate and the LDAPS server shows the client certificate is sent by the FortiGate:

Configuring client certificate authentication on the LDAP server

Administrators can configure a FortiGate client certificate in the LDAP server configuration when the FortiGate connects to an LDAPS server that requires client certificate authentication.

config user ldap
    edit <ldap_server>
        set client-cert-auth {enable | disable}
        set client-cert <source>
    next
end

Example

In this example, the FortiGate is configured as an explicit web proxy. It connects to the Windows AD server through LDAPS, where the Windows server requires a client certificate to connect. The client certificate is configured in the CLI.

The endpoint PC connecting to the web server will first need to authenticate to the explicit web proxy before accessing the server.

While this example demonstrates an LDAP client certificate for an explicit proxy configuration, LDAP client certificates can be used in firewall authentication, transparent proxy, ZTNA, and where ever LDAP configurations are used on the FortiGate.

To configure a client certificate on the LDAP server:
  1. Enable the explicit web proxy on port2:

    config system interface
        edit "port2"
            set explicit-web-proxy enable
        next
    end
  2. Upload the client certificate to the FortiGate:

    config vpn certificate local
        edit "Zach"
            set password **********
            set private-key <private key>
            set certificate <certificate>
        next
    end
  3. Configure the LDAP server settings:

    config user ldap
        edit "ldaps"
            set server "172.16.200.57"
            set server-identity-check disable
            set cnid "CN"
            set dn "CN=Users,DC=ftnt,DC=com"
            set secure ldaps
            set port 636
            set client-cert-auth enable
            set client-cert "Zach"
        next
    end
  4. Configure the authentication scheme:

    config authentication scheme
        edit "1"
            set method basic
            set user-database "ldaps"
        next
    end
  5. Configure the authentication rule:

    config authentication rule
        edit "1"
            set srcintf "port2"
            set srcaddr "all"
            set dstaddr "all"
            set active-auth-method "1"
        next
    end
  6. Configure the user group:

    config user group
        edit "test"
            set member "ldaps"
        next
    end
  7. Configure the proxy policy with the user group:

    config firewall proxy-policy
        edit 1
            set proxy explicit-web
            set dstintf "port3"
            set srcaddr "all"
            set dstaddr "all"
            set service "webproxy"
            set action accept
            set schedule "always"
            set srcaddr6 "all"
            set dstaddr6 "all"
            set groups "test"
            set utm-status enable
            set ssl-ssh-profile "deep-inspection-clone"
            set av-profile "av"
        next
    end

Testing and verification

When traffic from the endpoint PC matches a policy and triggers authentication, the FortiGate starts the LDAPS TLS connection handshake with the Windows AD. The LDAPS server requests a client certificate to identify the FortiGate as a client. The FortiGate provides a configured client certificate, issued to zach.com, to the LDAPS server.

The following communication between the FortiGate and the LDAPS server shows the client certificate is sent by the FortiGate: