Documentation Contents

Java Authentication and Authorization Service (JAAS) Reference Guide

This guide covers the following topics:

• Introduction
  • Who Should Read This Document
  • Related Documentation
• Core Classes and Interfaces
  • Common Classes
    • Subject
    • Principals
    • Credentials
  • Authentication Classes and Interfaces
    • LoginContext
    • LoginModule
    • CallbackHandler
    • Callback
  • Authorization Classes
    • Policy
    • AuthPermission
    • PrivateCredentialPermission
• JAAS Tutorials and Sample Programs
• Appendix A: JAAS Settings in the java.security Security Properties File
• Appendix B: Example Login Configurations

Introduction

The Java Authentication and Authorization Service (JAAS) was introduced as an optional package (extension) to the Java 2 SDK, Standard Edition (J2SDK), v 1.3. JAAS was integrated into the J2SDK 1.4.

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. See Making Login Services Independent from Authentication Technologies for further information.

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(ies), 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. Unlike in the J2SDK 1.3 and earlier, where access control decisions are based solely on code location and code signers (a CodeSource), in the J2SDK 1.4 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 JAAS LoginModule Developer's Guide.

You may wish to first read the JAAS Authentication and JAAS Authorization tutorials 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:

• Java SE Security Architecture
• JAAS white paper
• Java SE Security Tutorial

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.

If you wish to learn more about the standard Pluggable Authentication Module (PAM) framework (JAAS implements a Java version of PAM), see Making Login Services Independent from Authentication Technologies.

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

• JAAS Authentication Tutorial
• JAAS Authorization Tutorial

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

• JAAS Authentication
• JAAS Authorization

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

Core Classes and Interfaces

• Common Classes
  • Subject, Principal, Credential (actually, any Object)
• Authentication Classes and Interfaces
  • LoginContext, LoginModule, CallbackHandler, Callback
• Authorization Classes
  • Policy, AuthPermission, PrivateCredentialPermission

Common Classes

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

A Subject may also own security-related attributes, which are referred to as 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 (described below) 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);

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();

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 Principal Set, 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 below). 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();

The doAs methods for performing an action as a particular Subject

    public static Object
        doAs(final Subject subject,
             final java.security.PrivilegedAction action);

    public static Object
        doAs(final Subject subject,
             final java.security.PrivilegedExceptionAction action)
             throws java.security.PrivilegedActionException;

Both methods first associate the specified subject with the current Thread's AccessControlContext, and then execute the action. This achieves the effect of having the action run as the subject. The first method can throw runtime exceptions but normal execution has it returning an Object from the run method of its action argument. The second method behaves similarly except that it can throw a checked exception from its PrivilegedExceptionAction run method. An AuthPermission with target "doAs" is required to call the doAs methods.

Subject.doAs Example

Here is an example utilizing the first doAs method. Assume that someone named "Bob" has been authenticated by a LoginContext (see the LoginContext section) and as a result a Subject was populated with a Principal of class com.ibm.security.Principal, and that Principal has the name "BOB". Also assume that a SecurityManager has been installed, and that the following exists in the access control policy (see the Policy section for more details on the policy file).

    // grant "BOB" permission to read the file "foo.txt"
    grant Principal com.ibm.security.Principal "BOB" {
        permission java.io.FilePermission "foo.txt", "read";
    };

Here is the sample application code:

    class ExampleAction implements java.security.PrivilegedAction {
        public Object run() {
            java.io.File f = new java.io.File("foo.txt");

            // the following call invokes a security check
            if (f.exists()) {
                System.out.println("File foo.txt exists");
            }
            return null;
        }
    }

    public class Example1 {
        public static void main(String[] args) {

            // Authenticate the subject, "BOB".
            // This process is described in the
            // LoginContext section.

            Subject bob;
            // Set bob to the Subject created during the
            // authentication process

            // perform "ExampleAction" as "BOB"
            Subject.doAs(bob, new ExampleAction());
        }
    }

During execution, ExampleAction will encounter a security check when it makes a call to f.exists(). However, since ExampleAction is running as "BOB", and the policy (above) grants the necessary FilePermission to "BOB", the ExampleAction will pass the security check. If the grant statement in the policy is altered (adding an incorrect CodeBase or changing the Principal to "MOE", for example), then a SecurityException will be thrown.

The doAsPrivileged methods

The following methods also perform an action as a particular Subject.

    public static Object doAsPrivileged(
        final Subject subject,
        final java.security.PrivilegedAction action,
        final java.security.AccessControlContext acc);

    public static Object doAsPrivileged(
        final Subject subject,
        final java.security.PrivilegedExceptionAction action,
        final java.security.AccessControlContext acc)
        throws java.security.PrivilegedActionException;

An AuthPermission with target "doAsPrivileged" is required to call the doAsPrivileged methods.

doAs versus doAsPrivileged

The doAsPrivileged methods behave exactly the same as the doAs methods, except that instead of associating the provided Subject with the current Thread's AccessControlContext, they use the provided AccessControlContext. In this way, actions can be restricted by AccessControlContexts different from the current one.

An AccessControlContext contains information about all the code executed since the AccessControlContext was instantiated, including the code location and the permissions the code is granted by the policy. In order for an access control check to succeed, the policy must grant each code item referenced by the AccessControlContext the required permissions.

If the AccessControlContext provided to doAsPrivileged is null, then the action is not restricted by a separate AccessControlContext. One example where this may be useful is in a server environment. A server may authenticate multiple incoming requests and perform a separate doAs operation for each request. To start each doAs action "fresh," and without the restrictions of the current server AccessControlContext, the server can call doAsPrivileged and pass in a null AccessControlContext.

Principals

Credentials

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();

    void refresh() throws RefreshFailedException;

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();

    void destroy() throws DestroyFailedException;

Authentication Classes and Interfaces

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 authentication classes are described below.

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

See the CallbackHandler section 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 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.

     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

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

Authorization Classes

To make JAAS authorization take place, granting access control permissions based not just on what code is running but also on who is running it, the following is required:

• The user must be authenticated, as described in the LoginContext section.
• The Subject that is the result of authentication must be associated with an access control context, as described in the Subject section.
• Principal-based entries must be configured in the security policy, as described below.

The Policy abstract class and the authorization-specific classes AuthPermission and PrivateCredentialPermission are described below.

Policy

The java.security.Policy class is an abstract class for representing the system-wide access control policy. The Policy API was upgraded in the J2SDK 1.4 to support Principal-based queries.

As a default, the J2SDK provides a file-based subclass implementation, which was upgraded to support Principal-based grant entries in policy files.

Policy files and the structure of entries within them are described in Default Policy Implementation and Policy File Syntax.

AuthPermission

The javax.security.auth.AuthPermission class encapsulates the basic permissions required for JAAS. An AuthPermission contains a name (also referred to as a "target name") but no actions list; you either have the named permission or you don't.

In addition to its inherited methods (from the java.security.Permission class), an AuthPermission has two public constructors:

    public AuthPermission(String name);
    public AuthPermission(String name, String actions);

Currently the AuthPermission object is used to guard access to the Policy, Subject, LoginContext, and Configuration objects. Please refer to the AuthPermission javadocs for the list of valid names that are supported.

PrivateCredentialPermission

The javax.security.auth.PrivateCredentialPermission class protects access to a Subject's private credentials and provides one public constructor:

     public PrivateCredentialPermission(String name, String actions);

JAAS Tutorials and Sample Programs

The JAAS Authentication and JAAS Authorization tutorials contain the following samples:

• SampleAcn.java is a sample application demonstrating JAAS authentication.
• SampleAzn.java is a sample application used by the authorization tutorial. It demonstrates both authentication and authorization.
• sample_jaas.config is a sample login configuration file used by both tutorials.
• sampleacn.policy is a sample policy file granting permissions required by the code for the authentication tutorial.
• sampleazn.policy is a sample policy file granting permissions required by the code for the authorization tutorial.
• SampleLoginModule.java is the class specified by the tutorials' login configuration file (sample_jaas.config) as the class implementing the desired underlying authentication. SampleLoginModule's user authentication consists of simply verifying that the name and password specified by the user have specific values.
• SamplePrincipal.java is a sample class implementing the Principal interface. It is used by SampleLoginModule.

See the tutorials for detailed information about the applications, the policy files, and the login configuration file.

Application writers do not need to understand the code for SampleLoginModule.java or SamplePrincipal.java, as explained in the tutorials. Programmers who wish to write LoginModules can learn how to do so by reading the JAAS LoginModule Developer's Guide.

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 lib/security directory of the Java runtime.

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 properties. The default java.security file also lists a value for the login.config.url.n property, but it is commented out. In the example below, it is not commented.

...

#
# Class to instantiate as the javax.security.auth.login.Configuration
# provider.
#
login.configuration.provider=com.sun.security.auth.login.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.
#
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:${java.home}/lib/security/java.policy
policy.url.2=file:${user.home}/.java.policy

...

Note: Modifications made to this file may be overwritten by subsequent JRE 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

  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

Policy Provider

The default policy implementation can be replaced by specifying the alternative provider class implementation in the policy.provider property.

For example:

  policy.provider=com.foo.Policy

  policy.provider=sun.security.provider.PolicyFile

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

Policy File URLs

The location of the access control policy files can be statically set by specifying their respective URLs in the auth.policy.url.n property. 'n' is a consecutively numbered integer starting with 1. If multiple policies are specified (if n >= 2), they will be read and unioned into one single policy.

For example:

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

If the location of the policy file(s) is not set in the java.security properties file, and is not specified dynamically from the command line (via the -Djava.security.policy option), the access control policy defaults to the same policy as that of the system policy file installed with the J2SDK. That policy file

• grants all permissions to standard extensions
• allows anyone to listen on un-privileged ports
• allows any code to read certain "standard" properties that are not security-sensitive, such as the "os.name" and "file.separator" properties.

Appendix B: Example Login Configurations

Login configurations are located using the login.config.url.n security properties found in the java.security file. For more information about this property and the location of the java.security file, see Appendix A.

The default Configuration implementation, ConfigFile, gets its configuration information from login configuration files. For details about the default login Configuration implementation provided with JAAS, please consult the javadocs for the com.sun.security.auth.login.ConfigFile class.

The following is a sample login configuration file.

    Login1 {
       sample.SampleLoginModule required debug=true;
    };

    Login2 {
       sample.SampleLoginModule required;
       com.sun.security.auth.module.NTLoginModule sufficient;
       com.foo.SmartCard requisite debug=true;
       com.foo.Kerberos optional debug=true;
    };

The application Login1 only has one configured LoginModule, SampleLoginModule. Therefore, an attempt by Login1 to authenticate a subject (user or service) will be successful if and only if the SampleLoginModule succeeds.

The authentication logic for the application Login2 is easier to explain with the table below. Note: the required, sufficient, requisite, and optional flags are described in the Configuration javadocs.

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