Kerberos Single Sign On

#krb5.ini
[libdefaults]
  debug = true
  default_realm = YOURDOMAIN.DE
  dns_lookup_kdc = false
  default_keytab_name = FILE:C:\Program Files\custo diagnostic server\conf\tomcat.keytab
  krb4_config = /etc/krb.conf
  krb4_realms = /etc/krb.realms
  kdc_timesync = 1
  ccache_type = 4
  forwardable = true
  proxiable = true

[realms]
  YOURDOMAIN.DE = {
    kdc = tstdc01.yourdomain.de
    admin_server = tstdc01.yourdomain.de
    default_domain = yourdomain.de
} 

[domain_realm]

.adtest.local = YOURDOMAIN.DE 

[login]
krb4_convert = true
krb4_get_tickets = false

Introduction

This tutorial will guide you through the configuration of Kerberos for Single Sign On.

Please first configure LDAP and test it. When you configured LDAP correctly, you can move on with the following instructions to setup Kerberos SingleSign On.

Kerberos is a method that let you identify to other services with your windows logon. Having configured LDAP and Kerberos you can achieve Single Sign On which means, that custo diagnostic will automatically use the user that is logged on to Windows for authentication and the user does not need to enter any passwords.

Steps to configure the Kerberos System:

1. Create a normal domain user (used by Apache Tomcat to identify for Kerberos methos), "custoKerberos" .
2. Create a keytab-File - this file contains combines the use of Apache Tomcat ("Service Principal Name") to the user created above.
3. Configure Apache Tomcat to use the kerberos configuration
4. Enable Kerberos Identification in custo service center.

The first two steps has to be performed by an domain administrator.

Its worth to write down all information before you start.

E.g. In our Example we used the following names:

Create Domain User for Apache Tomcat

This step has to be done by the domain administrator.

Create a normal domain user. This user does not have to have specific access rights - but it must be able to authenticate/login with this user to the Windows Domain.

In our example we name the user  "custoKerberos", password "secretPW!"  (← don't take it in real life). the only membership is "Domain User". Please make sure, that the password does not have to be changed, and will not expire.

Create keytab-File

This step has to be done by the domain administrator.

Please use the following command to create the keytab-file.

ktpass -princ HTTP/win-tc01.yourdomain@YOURDOMAIN.DE
       -mapuser custoKerberos@yourdomain.de -crypto rc4-hmac-nt
       -ptype KRB5_NT_PRINCIPAL -pass secretPW!
       -out "C:\Program Files\custo diagnostic server\conf\tomcat.keytab"

This file contains the Tomcat private key for the service provider. To generate the file, run the following command as a domain administrator (all on a single line). You can do this step on the server where tomcat runs on.

Configure Apache Tomcat

Replace / Edit krb5.ini and jaas.conf file, located in your ...\custo diagnostic server\conf Directory:

#krb5.ini
[libdefaults]
  debug = true
  default_realm = YOURDOMAIN.DE
  dns_lookup_kdc = false
  default_keytab_name = FILE:C:\Program Files\custo diagnostic server\conf\tomcat.keytab
  krb4_config = /etc/krb.conf
  krb4_realms = /etc/krb.realms
  kdc_timesync = 1
  ccache_type = 4
  forwardable = true
  proxiable = true

[realms]
  YOURDOMAIN.DE = {
    kdc = tstdc01.yourdomain.de
    admin_server = tstdc01.yourdomain.de
    default_domain = yourdomain.de
} 

[domain_realm]

.adtest.local = YOURDOMAIN.DE 

[login]
krb4_convert = true
krb4_get_tickets = false

Kerberos

Kerberos lets you automatically login to the custo manager with you windows user if your user has a valid LDAP mapping. To do this you need to configure LDAP first.

Configuring Kerberos is somewhat complicated and for at least one step you need to be the Windows Domain Administrator. It involves configuring Tomcat (the application server that hosts the custo diagnostic server), so we use Tomcat as a synonym for custo diagnostic server at this place. Most of this manual is copied from https://tomcat.apache.org/tomcat-8.0-doc/windows-auth-howto.html

Kerberos (the basis for integrated Windows authentication) requires careful configuration. If the steps in this guide are followed exactly, then a working configuration will result. It is important that the steps below are followed exactly. There is very little scope for flexibility in the configuration. From the testing to date it is known that:

• The host name used to access the Tomcat server must match the host name in the SPN exactly else authentication will fail. A checksum error may be reported in the debug logs in this case.
• The SPN must be HTTP/<hostname> and it must be exactly the same in all the places it is used.
• The port number must not be included in the SPN.
• No more than one SPN may be mapped to a domain user.
• Tomcat must run as the domain account with which the SPN has been associated or as domain admin. It is NOT recommended to run Tomcat under a domain admin user.
• The domain name (DEV.LOCAL) is not case sensitive when used in the ktpass command, nor when used in jaas.conf
• The domain must be specified when using the ktpass command

There are three components to the configuration of the built-in Tomcat support for Windows authentication. The domain controller, the server hosting Tomcat, the web application wishing to use Windows authentication. The following sections describe the configuration required for each component.

The names of the three machines used in the configuration examples below are win-dc01.dev.local (the domain controller), win-tc01.dev.local (the Tomcat instance) and win-pc01.dev.local (client). All are members of the DEV.LOCAL domain.

Note: In order to use the passwords in the steps below, the domain password policy had to be relaxed. This is not recommended for production environments.

Domain Controller

These steps assume that the server has already been configured to act as a domain controller. Configuration of a Windows server as a domain controller is outside the scope of this how-to. The steps to configure the domain controller to enable Tomcat to support Windows authentication are as follows:

• Create a domain user that will be mapped to the service name used by the Tomcat server. In this how-to, this user is called tc01 and has a password of tc01pass.
• Map the service principal name (SPN) to the user account. SPNs take the form <service class>/<host>:<port>/<service name>. The SPN used in this how-to is HTTP/win-tc01.dev.local. To map the user to the SPN, run the following:

  setspn -A HTTP/win-tc01.dev.local tc01

• Generate the keytab file that the Tomcat server will use to authenticate itself to the domain controller. This file contains the Tomcat private key for the service provider account and should be protected accordingly. To generate the file, run the following command (all on a single line):

  ktpass /out c:\tomcat.keytab /mapuser tc01@DEV.LOCAL
            /princ HTTP/win-tc01.dev.local@DEV.LOCAL
            /pass tc01pass /kvno 0 /crypto ALL

• Create a domain user to be used on the client. In this how-to the domain user is test with a password of testpass.

The above steps have been tested on a domain controller running Windows Server 2008 R2 64-bit Standard using the Windows Server 2003 functional level for both the forest and the domain.

Configure Tomcat (the custo diagnostic server)

Copy the tomcat.keytab file created on the domain controller to <custo diagnostic server installation directory>/conf/tomcat.keytab.

Edit the file <custo diagnostic server installation directory>/conf/krb5.ini so it looks like this:

Edit the file <custo diagnostic server installation directory>/conf/jaas.conf so it looks like this:

Note the correct usage of forward and backward slashes when editing the files.

Please copy the editied files and the keytab file to a save location. 

Now you can change Login Method to Remote User:

As the last step, please restart the custo diagnostic server now.

For testing Kerberos authentication without using the custo manager, you can use the curl utility that is installed in the same folder as the custo diagnostic client:

If everything works and the logged in windows user is allowed to use custo diagnostic then this command should return "true".