The goal of this exercise is to learn how to use the Java
Authentication and Authorization (JAAS) API to perform
JAAS provides a standard pluggable authentication framework (PAM) for the Java platform. An application uses the JAAS API to perform authentication - the process of verifying the identity of the user who is using the application and gathering his identity information into a container called a subject. The application can then use the identity information in the subject along with the JAAS API to make authorization decisions, to decide whether the authenticated user is allowed to access protected resources or perform restricted actions. This exercise demonstrates JAAS Authentication. It does not demonstrate JAAS Authorization.
Read the Jaas.java sample code. The code performs the following tasks:
Subject.doAs will run the code defined in
MyAction as the authenticated user [lines 14-15]. This
serves two purposes. First, code in
MyAction that requires
identity information for authentication to a service could get it
from the subject. This exercise demonstrates this use. Second, if
MyAction accesses any protected resources/operations, the
identity information in the current subject would be used to make
the corresponding access control decision. This second aspect is
not covered in this exercise.
%JAVA_HOME%/binis in the
This exercise introduced the main classes of the JAAS APIs:
Subject. You learned how
LoginContext to authenticate a user and collect
its identity information in a
Subject. You then
learned how to use the
Subject to perform an action as
the authenticated user.
Proceed to Exercise 2 to learn how to configure the sample application to use Kerberos for authentication.
Kerberos is an Internet standard protocol for trusted-third party authentication defined in RFC 4120. It is available on most modern computing platforms today, including Solaris, Windows XP, and Linux.
The Kerberos architecture is centered around a trusted authentication service called the key distribution center, or KDC. Users and services in a Kerberos environment are referred to as principals; each principal shares a secret (such as a password) with the KDC. A principal authenticates to Kerberos by proving to the KDC that it knows the shared secret. If the authentication is successful, the KDC issues a ticket-granting-ticket (TGT) to the principal. When the principal subsequently wants to authenticate to a service on the network, such as a directory service or a file service, (thereby, acting as a "client" of the service), it gives the TGT to the KDC to obtain a service ticket to communicate with the service. Not only does the service ticket indicate the identities of the client and service principals, it also contains a session key that can be used by the client and service to subsequently establish secure communication. To authenticate to the service, the client sends the service ticket to the service. When the service receives the ticket, it decodes it using the secret it shares with the KDC.
In this architecture, a principal only authenticates directly (once) to the KDC. It authenticates indirectly to all other services via the use of service tickets. Service tickets are how the KDC vouches for the identity of a principal. The ability of a principal to access multiple secure services by performing explicit authentication only once is called single sign-on.
In JAAS, for a client principal, "logging into Kerberos" means
acquiring the TGT and placing it in the
that it can be used for authentication with services that the
client will access. For a service principal, "logging into
Kerberos" means obtaining the secret keys that the service needs to
decode incoming client authentication requests.
jaas-krb5.conf configuration file.
This file contains two entries, one named client and one named
server. The client entry indicates that the
LoginContext must use the
The server entry indicates that the
LoginContext must use the
same login module, and use keys from the
sample.keytab file for the principal
Edit this file and change the entry for server principal to use the name of your machine. For example, if your machine name is j1hol-001, this line in the configuration file should look like this:
Perform client authentication by typing the following command:
% java -Djava.security.auth.login.config=jaas-krb5.conf Jaas client
You will be prompted for a password. You should see the following output. Replace password with a password that is secure.
Kerberos password for test: password Authenticated principal: [test@J1LABS.EXAMPLE.COM] Performing secure action...
Perform server authentication by typing the following command:
% java -Djava.security.auth.login.config=jaas-krb5.conf Jaas server
You should see the following output:
Authenticated principal: [host/j1hol-001@J1LABS.EXAMPLE.COM] Performing secure action...
In this exercise, you learned how to configure a JAAS application to use a Kerberos login module, both as a client principal who enters his/her username/password interactively, and as a service principal who gets its keys from a keytab file.
Proceed to Part II to learn how to establish secure communication channels using Java security APIs.