Java Authentication and Authorization Service (JAAS) Reference Guide

JAAS can be used for two purposes:

  • for authentication of users, to reliably and securely determine who is currently executing Java code, regardless of whether the code is running as an application, an applet, a bean, or a servlet; and
  • for authorization of users to ensure they have the access control rights (permissions) required to do the actions performed.

JAAS implements a Java version of the standard Pluggable Authentication Module (PAM) framework.

Traditionally Java has provided codesource-based access controls (access controls based on where the code originated from and who signed the code). It lacked, however, the ability to additionally enforce access controls based on who runs the code. JAAS provides a framework that augments the Java security architecture with such support.

JAAS authentication is performed in a pluggable fashion. This permits applications to remain independent from underlying authentication technologies. New or updated authentication technologies can be plugged under an application without requiring modifications to the application itself. Applications enable the authentication process by instantiating a LoginContext object, which in turn references a Configuration to determine the authentication technology or technologies, or LoginModule(s), to be used in performing the authentication. Typical LoginModules may prompt for and verify a user name and password. Others may read and verify a voice or fingerprint sample.

Once the user or service executing the code has been authenticated, the JAAS authorization component works in conjunction with the core Java SE access control model to protect access to sensitive resources. Access control decisions are based both on the executing code's CodeSource and on the user or service running the code, who is represented by a Subject object. The Subject is updated by a LoginModule with relevant Principals and credentials if authentication succeeds.

Who Should Read This Document

This document is intended for experienced developers who require the ability to design applications constrained by a CodeSource-based and Subject-based security model. It is also intended to be read by LoginModule developers (developers implementing an authentication technology) prior to reading the Java Authentication and Authorization Service (JAAS): LoginModule Developer's Guide.

You may wish to first read JAAS Authentication Tutorial and java-authentication-authorization-service-jaas-reference-guide.html to get an overview of how to use JAAS and to see sample code in action, and then return to this document for further information.

Related Documentation

This document assumes you have already read the following:

A supplement to this guide is the JAAS LoginModule Developer's Guide, intended for experienced programmers who require the ability to write a LoginModule implementing an authentication technology.

The following tutorials for JAAS authentication and authorization can be run by everyone:

Similar tutorials for JAAS authentication and authorization, but which demonstrate the use of a Kerberos LoginModule and thus which require a Kerberos installation, can be found at

These two tutorials are a part of Introduction to JAAS and Java GSS-API Tutorials that utilize Kerberos as the underlying technology for authentication and secure communication.

Core Classes and Interfaces

The JAAS-related core classes and interfaces can be broken into three categories: Common, Authentication, and Authorization.

Common Classes

Common classes are those shared by both the JAAS authentication and authorization components.

The key JAAS class is javax.security.auth.Subject, which represents a grouping of related information for a single entity such as a person. It encompasses the entity's Principals, public credentials, and private credentials.

Note that the java.security.Principal interface is used to represent a Principal. Also note that a credential, as defined by JAAS, may be any Object.

Subject

To authorize access to resources, applications first need to authenticate the source of the request. The JAAS framework defines the term subject to represent the source of a request. A subject may be any entity, such as a person or a service. Once the subject is authenticated, a javax.security.auth.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") and a SSN Principal ("123-45-6789"), which distinguish it from other subjects.

A Subject may also own security-related attributes, which are referred to as credentials; see the section Credentials. Sensitive credentials that require special protection, such as private cryptographic keys, are stored within a private credential Set. Credentials intended to be shared, such as public key certificates, are stored within a public credential Set. Different permissions are required to access and modify the different credential Sets.

Subjects are created using these constructors:

    public Subject();

    public Subject(boolean readOnly, Set principals,
                   Set pubCredentials, Set privCredentials);

The first constructor creates a Subject with empty (non-null) Sets of Principals and credentials. The second constructor creates a Subject with the specified Sets of Principals and credentials. It also has a boolean argument which can be used to make the Subject read-only. In a read-only Subject, the Principal and credential Sets are immutable.

An application writer does not have to instantiate a Subject. If the application instantiates a LoginContext and does not pass a Subject to the LoginContext constructor, the LoginContext instantiates a new empty Subject. See the LoginContext section.

If a Subject was not instantiated to be in a read-only state, it can be set read-only by calling the following method: 

    public void setReadOnly();

A javax.security.auth.AuthPermission with target "setReadOnly" is required to invoke this method. Once in a read-only state, any attempt to add or remove Principals or credentials will result in an IllegalStateException being thrown. The following method may be called to test a Subject's read-only state: 

    public boolean isReadOnly();

To retrieve the Principals associated with a Subject, two methods are available: 

    public Set getPrincipals();
    public Set getPrincipals(Class c);

The first method returns all Principals contained in the Subject, while the second method only returns those Principals that are an instance of the specified Class c, or an instance of a subclass of Class c. An empty set will be returned if the Subject does not have any associated Principals.

To retrieve the public credentials associated with a Subject, these methods are available: 

    public Set getPublicCredentials();
    public Set getPublicCredentials(Class c);

The behavior of these methods is similar to that for the getPrincipals methods, except in this case the public credentials are being obtained.

To access private credentials associated with a Subject, the following methods are available: 

    public Set getPrivateCredentials();
    public Set getPrivateCredentials(Class c);

The behavior of these methods is similar to that for the getPrincipals and getPublicCredentials methods.

To modify or operate upon a Subject's PrincipalSet, public credential Set, or private credential Set, callers use the methods defined in the java.util.Set class. The following example demonstrates this: 

    Subject subject;
    Principal principal;
    Object credential;

    . . .

    // add a Principal and credential to the Subject
    subject.getPrincipals().add(principal);
    subject.getPublicCredentials().add(credential);

Note: An AuthPermission with target "modifyPrincipals", "modifyPublicCredentials", or "modifyPrivateCredentials" is required to modify the respective Sets. Also note that only the sets returned via the getPrincipals(), getPublicCredentials(), and getPrivateCredentials() methods with no arguments are backed by the Subject's respective internal sets. Therefore any modification to the returned set affects the internal sets as well. The sets returned via the getPrincipals(Class c), getPublicCredentials(Class c), and getPrivateCredentials(Class c) methods are not backed by the Subject's respective internal sets. A new set is created and returned for each such method invocation. Modifications to these sets will not affect the Subject's internal sets.

In order to iterate through a Set of private credentials, you need a javax.security.auth.PrivateCredentialPermission to access each credential. See the PrivateCredentialPermission API documentation for further information.

A Subject may be associated with an AccessControlContext (see the doAs and doAsPrivileged method descriptions in the following sections). The following method returns the Subject associated with the specified AccessControlContext, or null if no Subject is associated with the specified AccessControlContext. 

    public static Subject getSubject(final AccessControlContext acc);

An AuthPermission with target "getSubject" is required to call Subject.getSubject.

The Subject class also includes the following methods inherited from java.lang.Object. 

    public boolean equals(Object o);
    public String toString();
    public int hashCode();
Principals

As mentioned previously, once a Subject is authenticated, it is populated with associated identities, or Principals. A Subject may have many Principals. For example, a person may have a name Principal ("John Doe") and an SSN Principal ("123-45-6789"), which distinguish it from other Subjects. A Principal must implement the java.security.Principal and java.io.Serializable interfaces. See Subject for information about ways to update the Principals associated with a Subject.

Credentials

In addition to associated Principals, a Subject may own security-related attributes, which are referred to as credentials. A credential may contain information used to authenticate the subject to new services. Such credentials include passwords, Kerberos tickets, and public key certificates. Credentials might also contain data that simply enables the subject to perform certain activities. Cryptographic keys, for example, represent credentials that enable the subject to sign or encrypt data. Public and private credential classes are not part of the core JAAS class library. Any class, therefore, can represent a credential.

Public and private credential classes are not part of the core JAAS class library. Developers, however, may elect to have their credential classes implement two interfaces related to credentials: Refreshable and Destroyable.

Refreshable

The javax.security.auth.Refreshable interface provides the capability for a credential to refresh itself. For example, a credential with a particular time-restricted lifespan may implement this interface to allow callers to refresh the time period for which it is valid. The interface has two abstract methods: 

    boolean isCurrent();

This method determines whether the credential is current or valid. 

    void refresh() throws RefreshFailedException;

This method updates or extends the validity of the credential. The method implementation should perform an

AuthPermission("refreshCredential")

security check to ensure the caller has permission to refresh the credential.

Destroyable

The javax.security.auth.Destroyable interface provides the capability of destroying the contents within a credential. The interface has two abstract methods: 

    boolean isDestroyed();

Determines whether the credential has been destroyed.

    void destroy() throws DestroyFailedException;

Destroys and clears the information associated with this credential. Subsequent calls to certain methods on this credential will result in an IllegalStateException being thrown. The method implementation should perform an AuthPermission("destroyCredential") security check to ensure the caller has permission to destroy the credential.

Authentication Classes and Interfaces

Authentication represents the process by which the identity of a subject is verified, and must be performed in a secure fashion; otherwise a perpetrator may impersonate others to gain access to a system. Authentication typically involves the subject demonstrating some form of evidence to prove its identity. Such evidence may be information only the subject would likely know or have (such as a password or fingerprint), or it may be information only the subject could produce (such as signed data using a private key).

To authenticate a subject (user or service), the following steps are performed:

  1. An application instantiates a LoginContext.
  2. The LoginContext consults a Configuration to load all of the LoginModules configured for that application.
  3. The application invokes the LoginContext's login method.
  4. The login method invokes all of the loaded LoginModules. Each LoginModule attempts to authenticate the subject. Upon success, LoginModules associate relevant Principals and credentials with a Subject object that represents the subject being authenticated.
  5. The LoginContext returns the authentication status to the application.
  6. If authentication succeeded, the application retrieves the Subject from the LoginContext.

The following sections describe the authentication classes.

LoginContext

The javax.security.auth.login.LoginContext class provides the basic methods used to authenticate subjects, and provides a way to develop an application independent of the underlying authentication technology. The LoginContext consults a Configuration to determine the authentication services, or LoginModule(s), configured for a particular application. Therefore, different LoginModules can be plugged in under an application without requiring any modifications to the application itself.

LoginContext offers four constructors from which to choose: 

    public LoginContext(String name) throws LoginException;

    public LoginContext(String name, Subject subject) throws LoginException;

    public LoginContext(String name, CallbackHandler callbackHandler)
           throws LoginException

    public LoginContext(String name, Subject subject,
           CallbackHandler callbackHandler) throws LoginException

All of the constructors share a common parameter: name. This argument is used by the LoginContext as an index into the login Configuration to determine which LoginModules are configured for the application instantiating the LoginContext. Constructors that do not take a Subject as an input parameter instantiate a new Subject. Null inputs are disallowed for all constructors. Callers require an AuthPermission with target "createLoginContext.<name>" to instantiate a LoginContext. Here, <name> refers to the name of the login configuration entry that the application references in the name parameter for the LoginContext instantiation.

See CallbackHandler for information on what a CallbackHandler is and when you may need one.

Actual authentication occurs with a call to the following method:

    public void login() throws LoginException;

When login is invoked, all of the configured LoginModules are invoked to perform the authentication. If the authentication succeeded, the Subject (which may now hold Principals, public credentials, and private credentials) can be retrieved by using the following method: 

     public Subject getSubject();

To logout a Subject and remove its authenticated Principals and credentials, the following method is provided: 

    public void logout() throws LoginException;

The following code sample demonstrates the calls necessary to authenticate and logout a Subject:

    // let the LoginContext instantiate a new Subject
    LoginContext lc = new LoginContext("entryFoo");
    try {
        // authenticate the Subject
        lc.login();
        System.out.println("authentication successful");

        // get the authenticated Subject
        Subject subject = lc.getSubject();

        ...

        // all finished -- logout
        lc.logout();
    } catch (LoginException le) {
        System.err.println("authentication unsuccessful: " +
            le.getMessage());
    }
LoginModule

The LoginModule interface gives developers the ability to implement different kinds of authentication technologies that can be plugged in under an application. For example, one type of LoginModule may perform a user name/password-based form of authentication. Other LoginModules may interface to hardware devices such as smart cards or biometric devices.

Note: If you are an application writer, you do not need to understand the workings of LoginModules. All you have to know is how to write your application and specify configuration information (such as in a login configuration file) such that the application will be able to utilize the LoginModule specified by the configuration to authenticate the user.

If, on the other hand, you are a programmer who wishes to write a LoginModule implementing an authentication technology, see the Java Authentication and Authorization Service (JAAS): LoginModule Developer's Guide for detailed step-by-step instructions.

CallbackHandler

In some cases a LoginModule must communicate with the user to obtain authentication information. LoginModules use a javax.security.auth.callback.CallbackHandler for this purpose. Applications implement the CallbackHandler interface and pass it to the LoginContext, which forwards it directly to the underlying LoginModules. A LoginModule uses the CallbackHandler both to gather input from users (such as a password or smart card pin number) or to supply information to users (such as status information). By allowing the application to specify the CallbackHandler, underlying LoginModules can remain independent of the different ways applications interact with users. For example, the implementation of a CallbackHandler for a GUI application might display a window to solicit input from a user. On the other hand, the implementation of a CallbackHandler for a non-GUI tool might simply prompt the user for input directly from the command line.

CallbackHandler

is an interface with one method to implement:

     void handle(Callback[] callbacks)
         throws java.io.IOException, UnsupportedCallbackException;

The LoginModule passes the CallbackHandler handle method an array of appropriate Callbacks, for example a NameCallback for the user name and a PasswordCallback for the password, and the CallbackHandler performs the requested user interaction and sets appropriate values in the Callbacks. For example, to process a NameCallback, the CallbackHandler may prompt for a name, retrieve the value from the user, and call the NameCallback's setName method to store the name.

The CallbackHandler documentation has a lengthy example not included in this document that readers may want to examine.

Callback

The javax.security.auth.callback package contains the Callback interface as well as several implementations. LoginModules may pass an array of Callbacks directly to the handle method of a CallbackHandler.

Please consult the various Callback APIs for more information on their use.

Appendix A: JAAS Settings in the java.security Security Properties File

A number of JAAS-related settings can be configured in the java.security master Security Properties file, which is located in the conf/security directory of the JDK.

JAAS adds two new security properties to java.security:

  • login.configuration.provider
  • login.config.url.n

The following pre-existing properties are also relevant for JAAS users:

  • policy.provider
  • policy.url.n

The following example demonstrates how to configure these properties. In this example, we leave the values provided in the default java.security file for the policy.provider, policy.url.n, and login.configuration.provider Security Properties. The default java.security file also lists a value for the login.config.url.n Security Property, but it is commented out. In the following example, it is not commented. 

...

#
# Class to instantiate as the javax.security.auth.login.Configuration
# provider.
#
login.configuration.provider=sun.security.provider.ConfigFile

#
# Default login configuration file
#
#login.config.url.1=file:${user.home}/.java.login.config

#
# Class to instantiate as the system Policy. This is the name of the class
# that will be used as the Policy object. The system class loader is used to
# locate this class.
#
policy.provider=sun.security.provider.PolicyFile

# The default is to have a single system-wide policy file,
# and a policy file in the user's home directory.
#
policy.url.1=file:${java.home}/conf/security/java.policy
policy.url.2=file:${user.home}/.java.policy

...

Note:

Modifications made to this file may be overwritten by subsequent JDK updates. However, an alternate java.security properties file may be specified from the command line via the system property java.security.properties=<URL>. This properties file appends to the system properties file. If both properties files specify values for the same key, the value from command-line properties file is selected, as it is the last one loaded.

Also, specifying java.security.properties==<URL> (using two equals signs), then that properties file will completely override the system properties file.

To disable the ability to specify an additional properties file from the command line, set the key security.overridePropertiesFile to false in the system properties file. It is set to true by default.

Login Configuration Provider

The default JAAS login configuration implementation provided by Oracle gets its configuration information from files and expects the information to be provided in a specific format shown in the tutorials.

The default JAAS login configuration implementation can be replaced by specifying the alternative provider class implementation in the login.configuration.provider property.

For example:

    login.configuration.provider=com.foo.Config

If the Security property login.configuration.provider is not found, or is left unspecified, then it is set to the default value: 

    login.configuration.provider=com.sun.security.auth.login.ConfigFile

Note that there is no means to dynamically set the login configuration provider from the command line.

Login Configuration URLs

If you are using a login configuration implementation that expects the configuration information to be specified in files (as does the default implementation from Oracle), the location of the login configuration file(s) can be statically set by specifying their respective URLs in the login.config.url.n property. 'n' is a consecutively numbered integer starting with 1. If multiple configuration files are specified (if n >= 2), they will be read and unioned into one single configuration.

For example:


  login.config.url.1=file:C:/config/.java.login.config
  login.config.url.2=file:C:/users/foo/.foo.login.config

If the location of the configuration files is not set in the java.security properties file, and also is not specified dynamically from the command line (via the -Djava.security.auth.login.config option), JAAS attempts to load a default configuration from 


file:${user.home}/.java.login.config