This example requires that Keycloak is configured with Kerberos/SPNEGO authentication. It's showing how the forwardable TGT is sent from the Keycloak auth-server to the application, which deserializes it and authenticates with it to further Kerberized service, which in the example is LDAP server.

Example is using built-in ApacheDS Kerberos server and the realm with preconfigured federation provider and gss delegation credential protocol mapper. It also needs to enable forwardable ticket support in Kerberos configuration and your browser.

Detailed steps:

1) Build and deploy this sample's WAR file. For this example, deploy on the same server that is running the Keycloak Server (the easiest way is to use Keycloak Demo distribution), although this is not required for real world scenarios.

If Keycloak Server is running locally, you can deploy the WAR using maven:

mvn wildfly:deploy

2) Open kerberosrealm.json file for edit. Find keyTab config property, and adjust the path to http.keytab file, which is in project's root directory, to be an absolute path. For example:

   "keyTab" : "/home/user1/devel/keycloak/examples/kerberos/http.keytab"

On Windows you have to use forward slashes or double backslashes (\) - e.g.c:/Users/User1/devel/keycloak/examples/kerberos/http.keytab.

You can also move the file to another location if you want. WARNING: In production, keytab file should be in secured location accessible only to the user under which the Keycloak server is running.

3) Run Keycloak server and import kerberosrealm.json into it through admin console. This will import realm with sample application and configured LDAP federation provider with Kerberos/SPNEGO authentication support enabled and with gss delegation credential protocol mapper added to the application.

Also if you are on Linux, make sure that record like:

127.0.0.1       localhost

is in your /etc/hosts before other records for the 127.0.0.1 host to avoid issues related to incompatible reverse lookup (Ensure the similar for other OS as well)

4) Install kerberos client. This is platform dependent. If you are on Fedora, Ubuntu or RHEL, you can install package freeipa-client, which contains Kerberos client and bunch of other stuff.

5) Configure Kerberos client (On linux it's in file /etc/krb5.conf ). You need to configure KEYCLOAK.ORG realm for host localhost and enable forwardable flag, which is needed for credential delegation example, as application needs to forward Kerberos ticket and authenticate with it against LDAP server. See this file for inspiration. On OS X the file to edit (or create) is /Library/Preferences/edu.mit.Kerberos with the same syntax as krb5.conf. On Windows the file to edit (or create) is c:\Windows\krb5.ini with the same syntax as krb5.conf.

WARNING: test-krb5.conf is just a sample configuration which contains insecure algorithms. Therefore it shouldn't be used in production.

6) Run ApacheDS based LDAP server. You can run the command like this (assuming you're in the kerberos directory with this example):

mvn exec:java -Pkerberos

This will also automatically import the LDIF from kerberos-example-users.ldif of kerberos example into the LDAP server. Replace with your own LDIF file if you want different users.

A bit more details about embedded Kerberos server in Executing Tests.

WARNING: ApacheDS kerberos server shouldn't be used in production.

7) Configure browser (Firefox, Chrome or other) and enable SPNEGO authentication and credential delegation for localhost . Consult the documentation of your browser and OS on how to do it. For example in Firefox it can be done by adding localhost to both network.negotiate-auth.trusted-uris and network.negotiate-auth.delegation-uris and switch network.negotiate-auth.allow-non-fqdn to true. A bit more details in Executing Tests.

8) Test the example. Obtain kerberos ticket by running command from Terminal / CMD:

kinit [email protected]

with password secret .

Then in your web browser open http://localhost:8080/kerberos-portal . You should be logged-in automatically through SPNEGO without displaying Keycloak login screen. Keycloak will also transmit the delegated GSS credential to the application inside access token and application will be able to login with this credential to the LDAP server and retrieve some data from it (Actually it just retrieve few simple data about authenticated user himself).

You followed the instructions, but things don't seem to be working. Follow these instructions to troubleshoot.

1) Make sure to use the default user in all Terminal / CMD sessions. Do not use 'sudo' or 'su'. The reason is that when you open Firefox, it will open within the context of currently signed in user. And it will use that user's Kerberos ticket to perform authentication. When you obtain Kerberos ticket using Terminal session, you have to be that same user, otherwise the ticket will not be visible to the browser.

Of course make sure to obtain the ticket:

kinit [email protected]

with password secret.

2) On Linux make sure that the first entry in your /etc/hosts file is:

127.0.0.1  localhost

Even if it already contains a similar entry like:

127.0.0.1  localhost.localdomain localhost

Make sure to insert the short one before the existing one.

3) Make sure you have properly adjusted the path to http.keytab file in kerberosrealm.json. On Windows either use / as path delimiter or \\ (two backslashes).

4) Make sure that you have configured Firefox attributes via about:config url, and set network.negotiate-auth.trusted-uris and network.negotiate-auth.delegation-uris to localhost, and network.negotiate-auth.allow-non-fqdn to true.

Here are some typical errors, and how to overcome them. It often helps to close and reopen browser, or restart servers in order for remedy to take effect.

There is an error when starting embedded LDAP server:

GSSException: Invalid name provided (Mechanism level: KrbException: Cannot locate default realm)

Make sure that krb5.conf file exists - location and file name is OS specific. See step no. 5 of the instructions.

Browser redirects to normal login screen. There are no errors in Wildfly log.

Make sure to perform kinit, and properly configure Firefox. See points no. 1, and no. 4 above.

Browser redirects to a normal login screen. There is a warning in Wildfly log:

11:31:48,267 WARN  [org.keycloak.federation.kerberos.impl.SPNEGOAuthenticator] (default task-6) GSS Context accepted, but no context initiator recognized. Check your kerberos configuration and reverse DNS lookup configuration

There is also a warning similar to the following in Embedded LDAP log:

11:31:47,923 WARN  [org.apache.directory.server.KERBEROS_LOG] No server entry found for kerberos principal name HTTP/[email protected]
11:31:47,925 WARN  [org.apache.directory.server.KERBEROS_LOG] Server not found in Kerberos database (7)

Make sure that 127.0.0.1 reverse resolution returns 'localhost'. See point no. 2 above.

Browser redirects to a normal login screen. There is a stacktrace in Wildfly log:

15:10:04,531 WARN  [org.keycloak.federation.kerberos.impl.SPNEGOAuthenticator] (default task-3) SPNEGO login failed: java.security.PrivilegedActionException: GSSException: Failure unspecified at GSS-API level (Mechanism level: Invalid argument (400) - Cannot find key of appropriate type to decrypt AP REP - DES3 CBC mode with SHA1-KD)
   at java.security.AccessController.doPrivileged(Native Method)
   at javax.security.auth.Subject.doAs(Subject.java:422)
   at org.keycloak.federation.kerberos.impl.SPNEGOAuthenticator.authenticate(SPNEGOAuthenticator.java:46)

Make sure http.keytab is available at the location specified in kerberosrealm.json. See point no. 3 above.

Browser opens /kerberos-portal page, but reports an error retrieving user details from LDAP. There is a stacktrace in Wildfly log:

15:29:39,685 ERROR [stderr] (default task-6) javax.naming.AuthenticationException: GSSAPI [Root exception is javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid credentials provided (Mechanism level: Server not found in Kerberos database (7) - Server not found in Kerberos database)]]
15:29:39,687 ERROR [stderr] (default task-6) 	at com.sun.jndi.ldap.sasl.LdapSasl.saslBind(LdapSasl.java:169)
15:29:39,687 ERROR [stderr] (default task-6) 	at com.sun.jndi.ldap.LdapClient.authenticate(LdapClient.java:236)
15:29:39,689 ERROR [stderr] (default task-6) 	at com.sun.jndi.ldap.LdapCtx.connect(LdapCtx.java:2788)

Make sure http.keytab is available in location specified in kerberosrealm.json. See point no. 3 above. Also delete embedded server's cache directory:

rm -rf /tmp/server-work-keycloakDS

17:32:19,825 ERROR [stderr] (default task-24) org.keycloak.common.util.KerberosSerializationUtils$KerberosSerializationException: Null credential given as input. Did you enable kerberos credential delegation for your web browser and mapping of gss credential to access token?, Java version: 1.8.0_60, runtime version: 1.8.0_60-b27, vendor: Oracle Corporation, os: 4.1.6-200.fc22.x86_64
17:32:19,826 ERROR [stderr] (default task-24) 	at org.keycloak.common.util.KerberosSerializationUtils.deserializeCredential(KerberosSerializationUtils.java:109)
17:32:19,827 ERROR [stderr] (default task-24) 	at org.keycloak.example.kerberos.GSSCredentialsClient.getUserFromLDAP(GSSCredentialsClient.java:42)

Make sure to properly configure Firefox. See point no. 4 above.