Description
This article describes how to configure Kerberos authentication for explicit Proxy on FortiProxy.
Solution
Windows Server general setup.
Kerberos environment - Windows Server setup.
1) For the test setup a Windows Server 2016 setup with domain configuration and active directory was used
2) Set the domain name MT-TEST.LOCAL (realm name).
Create AD users.
- testuser is a normal user (can be any existing domain user account).
- fortikerberos is the example user that will be used for creating the Kerberos ticket.
Recommendation: create username all in lowercase (even if against corporate standards).
- The account only requires 'domain users' membership.
- Password set to never expire.
- Set a very strong password.
Create a DNS record for FortiProxy.
Create a DNS A record mapping your FortiProxy IP address to the FQDN, for example:
FORTIPROXY.MT-TEST.LOCAL -> 10.0.0.240.
Generate the Kerberos keytab.
On Windows Server use the ktpass command through CMD to generate the Kerberos keytab.
Note that it is necessary to run CMD with 'Run as Admin' option.
An explanation of the ktpass syntax can be seen on the following Microsoft link: https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/ktpass
Syntax example:
ktpass -princ HTTP/<FQDN of FortiProxy>@REALM -mapuser fortiproxy@domain.com -pass <password> -crypto all -ptype KRB5_NT_PRINCIPAL -out fpx.keytab
Test example:
ktpass -princ HTTP/fortiproxy.mt-test.local@MT-TEST.LOCAL -mapuser fortiproxy@mt-test.local -pass 12345678 -crypto all -ptype KRB5_NT_PRINCIPAL -out fpx.keytab
Note that the principal parameter is case-sensitive.
The output after creating a successful keytab looks similar to the following:
Encode the output in base64.
Use the base64 command available in most Linux distros (or use any other available Base64 encoder) to encode the fpx.keytab file.
Use the base64 command available in most Linux distros (or use any other available Base64 encoder) to encode the fpx.keytab file.
Any LF (Line Feed) need to be deleted from the file.
Example of encoding in a Linux distribution:
base64 fpx.keytab > fpx.txt
FortiProxy configuration.
All of the settings can be done in CLI or in GUI.
base64 fpx.keytab > fpx.txt
FortiProxy configuration.
All of the settings can be done in CLI or in GUI.
Create LDAP Server instance.
From GUI go to User & Device -> LDAP Servers and create a new LDAP server object.
From GUI go to User & Device -> LDAP Servers and create a new LDAP server object.
# config user ldapDefine Kerberos as an authentication service.
edit "dc01" <----- Required for authorization
set server "10.0.0.10" <----- LDAP server IP, normally it is the same as KDC server
set cnid "sAMAccountName"
set dn "dc=mt-test,dc=local"
set type regular
set username "fortibind@mt-test.local”
set password <password>
next
end
Go to User & Device -> Kerberos and create a new Kerberos object:
# config user krb-keytabGo to User & Device -> Scheme and create an authentication scheme with method negotiate:
edit "http_service"
set principal "HTTP/fortiproxy.mt-test.local@MT-TEST.LOCAL" <<< Same as the principal name in the ktpass command on Windows Server
set ldap-server "dc01" <<< the defined ldap server for authorization
set keytab "BQIAAABNAAIACkJFUkJFUi5DT00ABEhUVFAAGlRPTllfRkdUXzEwMERfQS5CRVJCRVIuQ09NAAAAAQAAAAAKABcAEJQl0MHqovwplu7XzfENJzw=" <<< base64 encoded keytab data, created in step 5 of general setup
next
end
# config authentication schemeGo to User & Device -> Authentication Rule and create an authentication rule with the 'krb' scheme set as the default authentication method:
edit "krb"
set method negotiate
set negotiate-ntlm disable
set kerberos-keytab "krb_mttest"
next
end
# config authentication ruleCreate user group(s).
edit "kerberos"
set srcintf "port1"
set srcaddr "all"
set dstaddr "all"
set ip-based disable
set active-auth-method "krb"
next
end
Go to User & Device -> User Groups and create a new group:
# config user group <----- The group is used for kerberos authentication.Create firewall policy.
edit "testgrp"
set member "dc01"
# config match
edit 1
set server-name "dc01" <----- Same as ldap-server option in krb-keytab.
set group-name "CN=Domain Users,CN=Users, DC=mt-test,DC=local"
next
end
next
end
Go to Policy & Objects -> Policy and create a new 'Explicit Proxy policy':
# config firewall policyDiagnostics.
edit 0
set type explicit-web
set name "test"
set explicit-web-proxy "web-proxy"
set dstintf "port1"
set srcaddr "all"
set dstaddr "all"
set action accept
set schedule "always"
set service "webproxy"
set logtraffic all
set groups "testgrp"
set utm-status enable
next
end
Once the keytab is imported, check that it has been properly decoded.
It is similarly visible with the following command:
FPX # fnsysctl ls -la /tmp/ktClient side walkthrough.
drwxr--r-- 2 0 0 Fri May 29 10:19:05 2020 60 .
drwxrwxrwt 31 0 0 Fri May 29 10:28:49 2020 2260 ..
-rw-r--r-- 1 0 0 Fri May 29 10:19:05 2020 387 KEY-FILE
Check Kerberos is working.
Log on to the domain by using testuser.
Use the klist command to list ticket information.
In the below example, the client has received krbtgt, CIFS, and LDAP tickets.
As there has been no interaction with the FortiProxy, there are no references to it.
C:\Users\testuser>klistConfigure client.
Cached Tickets: (5)
#0> Client: testuser @ mt-test.local
Server: krbtgt/MT-TEST.LOCAL @ MT-TEST.LOCAL
KerbTicket Encryption Type: AES-256-CTS-HMAC-SHA1-96
Ticket Flags 0x60a00000 -> forwardable forwarded renewable pre_authent
Start Time: 12/6/2020 14:58:06 (local)
End Time: 12/7/2020 0:58:04 (local)
Renew Time: 12/13/2020 14:58:04 (local)
Session Key Type: AES-256-CTS-HMAC-SHA1-96
#1> Client: testuser @ mt-test.local
Server: krbtgt/MT-TEST.LOCAL @ MT-TEST.LOCAL
KerbTicket Encryption Type: AES-256-CTS-HMAC-SHA1-96
Ticket Flags 0x40e00000 -> forwardable renewable initial pre_authent
Start Time: 12/6/2020 14:58:04 (local)
End Time: 12/7/2020 0:58:04 (local)
Renew Time: 12/13/2020 14:58:04 (local)
Session Key Type: AES-256-CTS-HMAC-SHA1-96
#2> Client: testuser @ mt-test.local
Server: cifs/EthicsGradient.mt-test.local @ MT-TEST.LOCAL
KerbTicket Encryption Type: AES-256-CTS-HMAC-SHA1-96
Ticket Flags 0x40a40000 -> forwardable renewable pre_authent ok_as_delegate
Start Time: 12/6/2020 14:58:06 (local)
End Time: 12/7/2020 0:58:04 (local)
Renew Time: 12/13/2020 14:58:04 (local)
Session Key Type: AES-256-CTS-HMAC-SHA1-96
#3> Client: testuser @ mt-test.local
Server: ldap/EthicsGradient.mt-test.local @ MT-TEST.LOCAL
KerbTicket Encryption Type: AES-256-CTS-HMAC-SHA1-96
Ticket Flags 0x40a40000 -> forwardable renewable pre_authent ok_as_delegate
Start Time: 12/6/2020 14:58:06 (local)
End Time: 12/7/2020 0:58:04 (local)
Renew Time: 12/13/2020 14:58:04 (local)
Session Key Type: AES-256-CTS-HMAC-SHA1-96
#4> Client: testuser @ mt-test.local
Server: LDAP/EthicsGradient.mt-test.local/mt-test.local @ MT-TEST.LOCAL
KerbTicket Encryption Type: AES-256-CTS-HMAC-SHA1-96
Ticket Flags 0x40a40000 -> forwardable renewable pre_authent ok_as_delegate
Start Time: 12/6/2020 14:58:06 (local)
End Time: 12/7/2020 0:58:04 (local)
Renew Time: 12/13/2020 14:58:04 (local)
Session Key Type: AES-256-CTS-HMAC-SHA1-96
In the Internet Options set the workstation to use FortiProxy as an internet proxy.
Specify the FQDN of the FortiProxy to ensure a Kerberos ticket is requested.
Push this information through a PAC file:
Open a connection to the Internet.
1) The client accesses the explicit proxy, but a HTTP 407 proxy authentication Required is returned.
2) As 'Negotiate' is set, the client has knowledge of the KRBTGT, it requests a ticket from the KDC with a krb-tgs-req message.
1) The client accesses the explicit proxy, but a HTTP 407 proxy authentication Required is returned.
2) As 'Negotiate' is set, the client has knowledge of the KRBTGT, it requests a ticket from the KDC with a krb-tgs-req message.
This includes the REALM (MT-TEST.LOCAL) in the reg-body section, and the provided instances SNAME and service (in this case, HTTP/dc01.mt-test.local).
3) The KDC responds with a next KRB-TGS-REP.
This ticket is then available on the client.
In the example below, the ticket-granted-service has issued Ticket #2.
The whole process takes less than a second to complete.
3) The KDC responds with a next KRB-TGS-REP.
This ticket is then available on the client.
In the example below, the ticket-granted-service has issued Ticket #2.
#2> Client: testuser @ mt-test.local4) The conversation between the client and the proxy continues, as the client responds with the Kerberos ticket in the response.
Server: HTTP/dc01.mt-test.local @ MT-TEST.LOCAL
KerbTicket Encryption Type: RSADSI RC4-HMAC(NT)
Ticket Flags 0x40a00000 -> forwardable renewable pre_authent
Start Time: 12/6/2020 14:59:45 (local)
End Time: 12/7/2020 0:58:04 (local)
Renew Time: 12/13/2020 14:58:04 (local)
Session Key Type: RSADSI RC4-HMAC(NT)
The whole process takes less than a second to complete.
The user is visible as a FSSO logon from GUI.
Note:
One of the reason the client does not show the ticket for the HTTP protocol under klist could be the encryption mismatch between client and the service where it needs to using the same Kerberos encryption type .
