Chapter 2. Introduction to JAAS
The JBossSX framework is based on the JAAS API. You must understand the basic elements of the JAAS API before you can understand the implementation details of JBossSX. The following sections provide an introduction to JAAS to prepare you for the JBossSX architecture discussion later in this guide.
The JAAS 1.0 API consists of a set of Java packages designed for user authentication and authorization. The API implements a Java version of the standard Pluggable Authentication Modules (PAM) framework and extends the Java 2 Platform access control architecture to support user-based authorization.
JAAS was first released as an extension package for JDK 1.3 and is bundled with JDK 1.5. Because the JBossSX framework only uses the authentication capabilities of JAAS to implement the declarative role-based J2EE security model, this introduction focuses on only that topic.
JAAS authentication is performed in a pluggable fashion. This permits Java applications to remain independent from underlying authentication technologies, and allows the JBossSX security manager to work in different security infrastructures. Integration with a security infrastructure is achievable without changing the JBossSX security manager implementation. You need only change the configuration of the authentication stack JAAS uses.
2.1. JAAS Core Classes
The JAAS core classes can be broken down into three categories: common, authentication, and authorization. The following list presents only the common and authentication classes because these are the specific classes used to implement the functionality of JBossSX covered in this chapter.
The are the common classes:
Subject(javax.security.auth.Subject)
These are the authentication classes:
Configuration(javax.security.auth.login.Configuration)LoginContext(javax.security.auth.login.LoginContext)
These are the associated interfaces:
Principal(java.security.Principal)Callback(javax.security.auth.callback.Callback)CallbackHandler(javax.security.auth.callback.CallbackHandler)LoginModule(javax.security.auth.spi.LoginModule)
2.1.1. Subject and Principal Classes
To authorize access to resources, applications must first authenticate the request's source. The JAAS framework defines the term subject to represent a request's source. The
Subject class is the central class in JAAS. A Subject represents information for a single entity, such as a person or service. It encompasses the entity's principals, public credentials, and private credentials. The JAAS APIs use the existing Java 2 java.security.Principal interface to represent a principal, which is essentially just a typed name.
During the authentication process, a subject is populated with associated identities, or principals. A subject may have many principals. For example, a person may have a name principal (John Doe), a social security number principal (123-45-6789), and a user name principal (johnd), all of which help distinguish the subject from other subjects. To retrieve the principals associated with a subject, two methods are available:
public Set getPrincipals() {...}
public Set getPrincipals(Class c) {...}
getPrincipals() returns all principals contained in the subject. getPrincipals(Class c) returns only those principals that are instances of class c or one of its subclasses. An empty set is returned if the subject has no matching principals.
Note that the
java.security.acl.Group interface is a sub-interface of java.security.Principal, so an instance in the principals set may represent a logical grouping of other principals or groups of principals.
2.1.2. Subject Authentication
Subject Authentication requires a JAAS log in. The log in process consists of the following points:
- An application instantiates a
LoginContextand passes in the name of the login configuration and aCallbackHandlerto populate theCallbackobjects, as required by the configurationLoginModules. - The
LoginContextconsults aConfigurationto load all theLoginModulesincluded in the named login configuration. If no such named configuration exists theotherconfiguration is used as a default. - The application invokes the
LoginContext.loginmethod. - The login method invokes all the loaded
LoginModules. As eachLoginModuleattempts to authenticate the subject, it invokes the handle method on the associatedCallbackHandlerto obtain the information required for the authentication process. The required information is passed to the handle method in the form of an array ofCallbackobjects. Upon success, theLoginModules associate relevant principals and credentials with the subject. - The
LoginContextreturns the authentication status to the application. Success is represented by a return from the log in method. Failure is represented through a LoginException being thrown by the log in method. - If authentication succeeds, the application retrieves the authenticated subject using the
LoginContext.getSubjectmethod. - After the scope of the subject authentication is complete, all principals and related information associated with the subject by the log in method can be removed by invoking the
LoginContext.logoutmethod.
The
LoginContext class provides the basic methods for authenticating subjects and offers a way to develop an application that is independent of the underlying authentication technology. The LoginContext consults a Configuration to determine the authentication services configured for a particular application. LoginModule classes represent the authentication services. Therefore, you can plug different login modules into an application without changing the application itself. The following code shows the steps required by an application to authenticate a subject.
CallbackHandler handler = new MyHandler();
LoginContext lc = new LoginContext("some-config", handler);
try {
lc.login();
Subject subject = lc.getSubject();
} catch(LoginException e) {
System.out.println("authentication failed");
e.printStackTrace();
}
// Perform work as authenticated Subject
// ...
// Scope of work complete, logout to remove authentication info
try {
lc.logout();
} catch(LoginException e) {
System.out.println("logout failed");
e.printStackTrace();
}
// A sample MyHandler class
class MyHandler
implements CallbackHandler
{
public void handle(Callback[] callbacks) throws
IOException, UnsupportedCallbackException
{
for (int i = 0; i < callbacks.length; i++) {
if (callbacks[i] instanceof NameCallback) {
NameCallback nc = (NameCallback)callbacks[i];
nc.setName(username);
} else if (callbacks[i] instanceof PasswordCallback) {
PasswordCallback pc = (PasswordCallback)callbacks[i];
pc.setPassword(password);
} else {
throw new UnsupportedCallbackException(callbacks[i],
"Unrecognized Callback");
}
}
}
}
Developers integrate with an authentication technology by creating an implementation of the
LoginModule interface. This allows an administrator to plug different authentication technologies into an application. You can chain together multiple LoginModules to allow for more than one authentication technology to participate in the authentication process. For example, one LoginModule may perform user name/password-based authentication, while another may interface to hardware devices such as smart card readers or biometric authenticators.
The life cycle of a
LoginModule is driven by the LoginContext object against which the client creates and issues the log in method. The process consists of two phases. The steps of the process are as follows:
- The
LoginContextcreates each configuredLoginModuleusing its public no-arg constructor. - Each
LoginModuleis initialized with a call to its initialize method. TheSubjectargument is guaranteed to be non-null. The signature of the initialize method is:public void initialize(Subject subject, CallbackHandler callbackHandler, Map sharedState, Map options) - The
loginmethod is called to start the authentication process. For example, a method implementation might prompt the user for a user name and password and then verify the information against data stored in a naming service such as NIS or LDAP. Alternative implementations might interface to smart cards and biometric devices, or simply extract user information from the underlying operating system. The validation of user identity by eachLoginModuleis considered phase 1 of JAAS authentication. The signature of theloginmethod isboolean login() throws LoginException. ALoginExceptionindicates failure. A return value of true indicates that the method succeeded, whereas a return value of false indicates that the login module should be ignored. - If the
LoginContext's overall authentication succeeds,commitis invoked on eachLoginModule. If phase 1 succeeds for aLoginModule, then the commit method continues with phase 2 and associates the relevant principals, public credentials, and/or private credentials with the subject. If phase 1 fails for aLoginModule, thencommitremoves any previously stored authentication state, such as user names or passwords. The signature of thecommitmethod is:boolean commit() throws LoginException. Failure to complete the commit phase is indicated by throwing aLoginException. A return of true indicates that the method succeeded, whereas a return of false indicates that the login module should be ignored. - If the
LoginContext's overall authentication fails, then theabortmethod is invoked on eachLoginModule. Theabortmethod removes or destroys any authentication state created by the log in or initialize methods. The signature of theabortmethod isboolean abort() throws LoginException. Failure to complete theabortphase is indicated by throwing aLoginException. A return of true indicates that the method succeeded, whereas a return of false indicates that the login module should be ignored. - To remove the authentication state after a successful log in, the application invokes
logouton theLoginContext. This in turn results in alogoutmethod invocation on eachLoginModule. Thelogoutmethod removes the principals and credentials originally associated with the subject during thecommitoperation. Credentials should be destroyed upon removal. The signature of thelogoutmethod is:boolean logout() throws LoginException. Failure to complete the logout process is indicated by throwing aLoginException. A return of true indicates that the method succeeded, whereas a return of false indicates that the login module should be ignored.
When a
LoginModule must communicate with the user to obtain authentication information, it uses a CallbackHandler object. Applications implement the CallbackHandler interface and pass it to the LoginContext, which send the authentication information directly to the underlying login modules.
Login modules use the
CallbackHandler both to gather input from users, such as a password or smart card PIN, and to supply information to users, such as status information. By allowing the application to specify the CallbackHandler, underlying LoginModules remain independent from the different ways applications interact with users. For example, a CallbackHandler's implementation for a GUI application might display a window to solicit user input. On the other hand, a CallbackHandler implementation for a non-GUI environment, such as an application server, might simply obtain credential information by using an application server API. The CallbackHandler interface has one method to implement:
void handle(Callback[] callbacks)
throws java.io.IOException,
UnsupportedCallbackException;
The
Callback interface is the last authentication class we will look at. This is a tagging interface for which several default implementations are provided, including the NameCallback and PasswordCallback used in an earlier example. A LoginModule uses a Callback to request information required by the authentication mechanism. LoginModules pass an array of Callbacks directly to the CallbackHandler.handle method during the authentication's log in phase. If a callbackhandler does not understand how to use a Callback object passed into the handle method, it throws an UnsupportedCallbackException to abort the login call.
