Creating a Kerberos configuration file

The Kerberos configuration file contains client configuration information, including the locations of Key Distribution Centers (KDCs) for the realms of interest, defaults for the current Kerberos realm and mappings of host names onto Kerberos realms. Use the wsadmin utility to create a Kerberos configuration file for WebSphere® Application Server.

About this task

Note: You can not use the createkrbConfigFile wsadmin command if you do not have a Kerberos keytab file (krb5.keytab).

Kerberos configuration settings, the Kerberos key distribution center (KDC) name, and realm settings for both Simple and Protected GSS-API Negotiation Mechanism (SPNEGO) web authentication and Kerberos authentication are provided in the Kerberos configuration file or through the java.security.krb5.kdc and java.security.krb5.realm Java™ virtual machine system properties.

If you do not have a Kerberos configuration file (krb5.ini or krb5.conf), you must first create a Kerberos configuration file and place it in every instance in a cell using a wsadmin command. See the following default Kerberos configuration files and their locations:

The default location is 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.
The default location is /etc/krb5.conf.
On other Unix platforms, the default location is /etc/krb5/krb5.conf.

Procedure

Start the command-line utility by running the wsadmin command from the app_server_root/bin directory.
At the wsadmin prompt, enter the following command:
```
$AdminTask help createKrbConfigFile 
```

Specify createKrbConfigFile command parameters.

Table 1. createKrbConfigFile command parameters .
This table lists the parameters you can use with the createKrbConfigFile command:
Option	Description
<krbPath>	Required. Provides the fully qualified file system location of the Kerberos configuration (krb5.ini or krb5.conf) file.
<realm>	Required. Provides the Kerberos realm name. The value of this attribute is used by SPNEGO to form the Kerberos service principal name for each of the hosts specified with the property com.ibm.ws.security.spnego.SPN<id>.hostName.
<kdcHost>	Required. Provides the host name of the Kerberos Key Distribution Center (KDC).
<kdcPort>	Optional. Provides the port number of the Kerberos Key Distribution Center. If this port is omitted, the default value is 88.
<dns>	Required. A list of default domain name services DNS, separated by a pipe character, that is used to produce a fully qualified host name. The first one in the list is the default domain name service.
<keytabPath>	Required. Provides the file system location of the Kerberos keytab path and file name.
<encryption>	Optional. Identifies the list of supported encryption types, separated by a pipe character.

Specify an encryption type.
The following encryption types are supported:
- aes128-cts-hmac-sha1-96
- aes256-cts-hmac-sha1-96
Attention: Not all of the KDC solutions available support all of the encryption types previously listed. Before you choose an encryption type, ensure that your KDC supports the encryption type that you want to use by consulting your Kerberos Administrator's and User's Guide.

Ensure you have a common encryption type for the Kerberos configuration file, the Kerberos keytab file, the Kerberos service principal name and the Kerberos client. For example, if the Kerberos client uses the aes128-cts-hmac-sha1-96 encryption type, the target server must also support the aes128-cts-hmac-sha1-96 encryption type and the Kerberos configuration file must list aes128-cts-hmac-sha1-96 first in default_tgt_enctypes and default_tkt_enctypes.
Specify the krbPath and krbKeytab location types.
The following code is an example of the createKrbConfigFile command:
```
$AdminTask createKrbConfigFile {-krbPath c:/winnt/krb5.ini 
                                -realm WSSEC.AUSTIN.IBM.COM 
                                -kdcHost host1.austin.ibm.com 
                                -dns austin.ibm.com|raleigh.ibm.com 
                                -keytabPath c:/winnt/krb5.keytab}
```
Note: WebSphere variables can also be used to specify krbPath and krbKeytab location paths for the createKrbConfigFile command.
Use this example to create the c:/winnt/krb5.ini file:
```
[libdefaults]
	default_realm = WSSEC.AUSTIN.IBM.COM
	default_keytab_name = FILE:c:\winnt\krb5.keytab
	default_tkt_enctypes = aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
	default_tgs_enctypes = aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96
	forwardable  = true
	renewable  = true
	noaddresses = true
	clockskew  = 300
[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
	.raleigh.ibm.com = WSSEC.AUSTIN.IBM.COM
```
The createKrbConfigFile command creates a simple Kerberos configuration file. You can edit this file, as needed, to specify a TCP or UDP preference or when you have a cross or trusted realm environment.
In the [libdefaults] section, you can specify a TCP or UDP protocol preference. By default, the Java Kerberos configuration uses the UDP protocol. However, the Java Kerberos supports a TCP or a UDP protocol configuration using the udp_preference_limit parameter. If you need to use the TCP protocol, specify the udp_preference_limit parameter with a 1 value to always use the TCP protocol. For example:
```
udp_preference_limit =1
```
If you do not specify this parameter, the Java Kerberos library uses the TCP protocol only if the Kerberos ticket request using the UDP protocol fails and the KDC returns the KRB_ERR_RESPONSE_TOO_BIG error code.
Avoid trouble: When the application server receives a client request, the Kerberos configuration on the server might return a Connection reset, IOException, or Broken pipe exception if you use the TCP protocol and the KDC returns a bad packet. The application server makes three attempts to capture the correct Kerberos packet. If a correct Kerberos packet is returned as a result of one of the three attempts, the client request is successfully processed and you can ignore the exceptions. If the application server cannot obtain the correct Kerberos packet after three attempts, the client request fails. At this point, review the KDC, network, and application server configurations to determine the issue.
Complete the [domain_realm] section of the Kerberos configuration file for a cross realm environment
- [domain_realm]: Provides a translation from a domain name or host name to a realm name. The tag name can be a host name or a domain name. Domain names are indicated by a prefix of a period ('.'). The value of the relation is the realm name for that particular host or domain. Host names and domain names must be lowercase.
  If no translation entry applies, the host realm is considered to be the host name domain portion converted to uppercase. For example, the following [domain_realm] section maps tech.ibm.com into the TEST.AUSTIN.IBM.COM realm:
  [domain_realm] .austin.ibm.com = WSSEC.AUSTIN.IBM.COM .raleigh.ibm.com = WSSEC.AUSTIN.IBM.COM
  All other hosts in the austin.ibm.com and .raleigh.ibm.com domains map to WSSEC.AUSTIN.IBM.COM by default.
  The following example contains more than one Kerberos realm name:
  [domain_realm] .ibm.com =AUSTIN.IBM.COM ibm.com =AUSTIN.IBM.COM tech.ibm.com =TEST.AUSTIN.IBM.COM .fubar.org =FUBAR.ORG
  All other hosts in the ibm.com® domain map by default to the AUSTIN.IBM.COM realm and all hosts in the fubar.org domain map by default to the FUBAR.ORG realm.
Note the entries for the hosts, ibm.com and fubar.org. Without these entries, these hosts map into the realms COM and ORG, respectively.

For peer trust cross-realm authentication, see your Kerberos Administrator's and User's Guide for information about how to set up the trust cross-realm authentication on the KDC.
Add information about the foreign realm to the realms and domain_realm sections of the Kerberos configuration file:
```
[realms]
       AUSTIN.IBM.COM = {
             kdc = kdc.austin.ibm.com:88
             default_domain = austin.ibm.com
       }
       FUBAR.ORG = {
             kdc = kdc.fubar.org:88
             default_domain = fubar.org
       }
[domain_realm]
       austin.ibm.com = AUSTIN.IBM.COM
       .austin.ibm.com = AUSTIN.IBM.COM
       fubar.org = FUBAR.ORG
       .fubar.org = FUBAR.ORG
```
In a transitive trust, two realms trust each other if they trust the intermediate realms involved in granting a ticket. If each realm involved in granting the service ticket is present in the trust path, then the ticket is trusted. See your Kerberos Administrator's and User's Guide for information about how to configure transitive trust on the KDC.
To set up transitive trust, separate realms with cross-realm authentication must be defined between A and B and between B and C, but not between A and C. With transitive trust, REALMA and REALMC can communicate with each other, but only by going through REALMB.
```
REALMA	<->	REALMB	<->	REALMC
```
Add data to stanzas.
Add a [capaths] stanza to each krb5.conf file.
The krb5.conf files on all machines must list all three realms in the [realms] stanza. REALMA must list itself and REALMB and REALMC; REALMB must list itself and REALMA and REALMC; REALMC must list itself and REALMA and REALMB. In the [domain_realm] stanza of the krb5.conf files list all three host names and realm names to be able to execute from REALMA to REALMC and from REALMC to REALMA.
```
[capaths]
       REALMA.AUSTIN.IBM.COM = {
       		REALMB.AUSTIN.IBM.COM = .
       		REALMC.AUSTIN.IBM.COM = REALMB.AUSTIN.IBM.COM
            }
       REALMB.AUSTIN.IBM.COM = {
       		REALMC.AUSTIN.IBM.COM = .
       		REALMA.AUSTIN.IBM.COM = .
            }
       REALMC.AUSTIN.IBM.COM = {
       		REALMB.AUSTIN.IBM.COM = .
       		REALMA.AUSTIN.IBM.COM = REALMB.AUSTIN.IBM.COM
            }
```
Set the krb5.conf file permission to 644.
This means that you can read and write the file. However, members of the group that the file belongs to and all other users can only read the file.

Since the Kerberos configuration and keytab file are set by the JVM system properties, java.security.krb5.conf and KRB5_KTNAME respectively, if SPNEGO web authentication and Kerberos authentication are both enabled you must use the same Kerberos configuration and keytab files for both.

Results

You have now created a Kerberos configuration file.