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.
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.
Code listing for
%JAVA_HOME%/binis in the path, and JDK pointed to by the
%JAVA_HOME%variable points to Java SE 6.
% cd auth/src % javac Jaas.javaYou will run this code in subsequent exercises after doing some set up. That ends this exercise.
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.
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.
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
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.
JAAS Background for this exercise:
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.
Resources for this exercise:
Steps to follow:
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
Code listing for
Output for running the JAAS example using the client
Output for running JAAS example using "server" entry from
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.
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