The Kerberos configuration file

The Kerberos configuration properties, krb5.ini or krb5.conf files, must be configured on every WebSphere® Application Server instance in a cell in order to use the Simple and Protected GSS-API Negotiation Mechanism (SPNEGO) trust association interceptor (TAI) for WebSphere Application Server.

Deprecated feature: In WebSphere Application Server Version 6.1, a trust association interceptor (TAI) that uses the Simple and Protected GSS-API Negotiation Mechanism (SPNEGO) to securely negotiate and authenticate HTTP requests for secured resources was introduced. In WebSphere Application Server 7.0, this function is now deprecated. SPNEGO web authentication has taken its place to provide dynamic reload of the SPNEGO filters and to enable fallback to the application login method.
The default Kerberos configuration file name for Windows is krb5.ini. For other platforms is the default Kerberos configuration file name is krb5.conf. The default location for the Kerberos configuration file is shown later in this section:
Table 1. Default locations for Kerberos configuration file . This table describes default locations for the Kerberos configuration file.
Operating System Default Location
Windows c:\winnt\krb5.ini
Note: If the krb5.ini file is not located in the c:\winnt directory it might be located in c:\windows directory.
Linux /etc/krb5.conf
other UNIX-based /etc/krb5/krb5.conf
z/OS /etc/krb5/krb5.conf
IBM i /QIBM/UserData/OS400/NetworkAuthentication/krb5.conf
Note: If you do not use the default location and Kerberos configuration file name, then you have to update *.krb5ConfigFile properties in the soap.client.prop, ipc.client.props, and sas.client.props files. Also, if the client programmatic login uses the WSKRBLogin module, you must also set the java.security.krb5.conf JVM property.

For SPNEGO TAI, if you do not use the default location and Kerberos configuration file name, then you must specify the java.security.krb5.conf JVM property.

The default Kerberos configuration file on Windows is /winnt/krb5.ini and on a distributed environment is /etc/krb5. If you specify another location path, then you must also specify the java.security.krb5.conf JVM property.

For example, if your krb5.conf file is specified at /opt/IBM/WebSphere/profiles/AppServer/etc/krb5.conf, then you need to specify -Djava.security.krb5.conf=/opt/IBM/WebSphere/profiles/AppServer/etc/krb5.conf.

The WebSphere runtime code searches for the Kerberos configuration file in the order as follows:
  1. The file referenced by the Java™ property java.security.krb5.conf
  2. <java.home>/lib/security/krb5.conf
  3. c:\winnt\krb5.ini on Microsoft Windows platforms
  4. /etc/krb5/krb5.conf on UNIX platforms
  5. /etc/krb5.conf on Linux platforms.
Use the wsadmin utility to configure the SPNEGO TAI for WebSphere Application Server:
  1. Start WebSphere Application Server.
  2. [AIX Solaris HP-UX Linux Windows][z/OS]Start the command-line utility by running the wsadmin command from the app_server_root/bin directory.
  3. [IBM i]Start the command-line utility by running the wsadmin command from the app_server_root/bin directory from the Qshell command line.
  4. At the wsadmin prompt, enter the following command: 
    $AdminTask createKrbConfigFile
    You can use the following parameters with this command:
    Table 2. Command parameters . This table describes parameters for the $AdminTask createKrbConfigFile command.
    Option Description
    <krbPath> This parameter is required. It provides the fully qualified file system location of the Kerberos configuration (krb5.ini or krb5.conf) file.
    <realm> This parameter is required. It provides the Kerberos realm name. The value of this attribute is used by the SPNEGO TAI to form the Kerberos service principal name for each of the hosts specified with the property com.ibm.ws.security.spnego.SPNid.hostName.
    <kdcHost> This parameter is required. It provides the host name of the Kerberos Key Distribution Center (KDC).
    <kdcPort> This parameter is optional. It provides the port number of the KDC. The default value, if not specified, is 88.
    <dns> This parameter is required. It provides the default domain name service (DNS) that is used to produce a fully qualified host name.
    <keytabPath> This parameter is required. It provides the file system location of the Kerberos keytab file.
    <encryption> This parameter is optional. It identifies the list of supported encryption types, separated by a space. The specified value is used for the default_tkt_enctypes and default_tgs_enctypes.

In the following example, the wsadmin command creates the krb5.ini file in the c:\winnt directory. The default Kerberos keytab file is also in c:\winnt. The actual Kerberos realm name is WSSEC.AUSTIN.IBM.COM and the KDC host name is host1.austin.ibm.com.

wsadmin>$AdminTask createKrbConfigFile {-krbPath 
c:\winnt\krb5.ini -realm WSSEC.AUSTIN.IBM.COM -kdcHost host1.austin.ibm.com
 -dns austin.ibm.com -keytabPath c:\winnt\krb5.keytab}
The previous wsadmin command creates a krb5.ini file as follows:
[libdefaults]
 default_realm = WSSEC.AUSTIN.IBM.COM
        default_keytab_name = FILE:c:\winnt\krb5.keytab
        default_tkt_enctypes = aes256-cts-hmac-sha1-96
        default_tgs_enctypes = aes256-cts-hmac-sha1-96
[realms]
        WSSEC.AUSTIN.IBM.COM = {
  kdc = host1.austin.ibm.com:88
              default_domain = austin.ibm.com        
}
[domain_realm]
        .austin.ibm.com = WSSEC.AUSTIN.IBM.COM
Attention:
  • [AIX Solaris HP-UX Linux Windows][IBM i]A Kerberos keytab file contains a list of keys that are analogous to user passwords. It is important for hosts to protect their Kerberos keytab files by storing them on the local disk. The krb5.conf file permission must be 644, which means that you can read and write the file; however, members of the group that the file belongs to, and all others can only read the file.
  • [z/OS]A Kerberos keytab file contains a list of keys that are analogous to user passwords. It is important for hosts to protect their Kerberos keytab files by storing them on the local disk. The krb5.conf file permission must be 644, which means that you can read and write the file; however, members of the group that the file belongs to, and all others can only read the file. The user ID that runs adjunct, control, and servants must have read access to the krb5.conf and krb5.keytab files.
[IBM i]The krb5.conf configuration file supports trigraphs to represent the {, }, [, and ] characters. These characters depend on the language set. The natively generated keytabs cannot be read by the Kerberos client. If you have difficulty configuring SPNEGO TAI with the native krb5.conf or krb5.keytab files, complete one of the following scenarios to address the trigraphs issue:
  • Replace the trigraphs in the krb5.conf file with the characters that they represent.
  • Use the krb5.conf file that is generated by WebSphere Application Server.
  • Use a Microsoft Windows or a key distribution center (KDC) generated keytab file.

Kerberos configuration settings, the Kerberos key distribution center (KDC) name, and realm settings for the Simple and Protected GSS-API Negotiation Mechanism (SPNEGO) trust association interceptor (TAI) are provided in the Kerberos configuration file or through java.security.krb5.kdc and java.security.krb5.realm system property files.