Developing With JAAS

Copyright 2003 Rizwan Ahmed

Implementing Java Security with JAAS

Rizwan AhmedSun Certified Professional

Implementing Java Security with

JAAS

Rizwan Ahmed © 2003


What is JAAS?

• Java Authentication and Authorization Service• Introduced as an optional package in J2SE 1.3• Integrated into J2SE 1.4• Provides a pluggable and flexible framework

that allows developers to incorporate different security mechanisms and sources


Goals

• JAAS is an extensive and complicated library.• The goals for this presentation are:

– To give an overview of JAAS and its constituent parts and illustrate how they all work together

– Provide an introduction on how to use JAAS; code examples to help you get started


Outline

• Introduction– What is JAAS– Authentication vs. Authorization– Subject– Principal

• Authentication• Authorization


Authentication vs. Authorization

• Authentication is the process of verifying the users’ identity. Typically this entails obtaining a user name and a password or some other credential from the user.

• Authorization is the process of verifying whether a user has access to protected resources.

Authentication

Andy

AuthenticationService

Is the user who hesays he is?

User NamePassword

Authorization

Andy

Resource

AuthorizationService

Some Action

Can this userperform this

action on me?


Overview of the Subject

• The Subject is a container for associated Principals, Public Credentials (public keys), and Private Credentials (passwords, private keys).

The Subject in Detail

Subject

PrincipalPrincipal

Principal

PublicCredential

PublicCredential

PublicCredential

PrivateCredential

PrivateCredential

PrivateCredential


Subject

A Subject in JAAS represents an authenticated entity such as a person or device

1. package javax.security.auth;2. public class Subject {3. ...4.5. public Set getPrincipals() {}6. public Set getPrincipals(Class c) {}7.8. public Set getPrivateCredentials() {}9. public Set getPrivateCredentials(Class c) {}10.11. public Set getPublicCredentials() {}12. public Set getPublicCredentials(Class c) {}13.14. public boolean isReadOnly() {}15. public void setReadOnly() {}16.}


Principal

• A Principal identifies a Subject. The Subject can be a person, a corporation, and application, etc.

• A Subject is comprised of a set of Principals, where each Principal represents an identity for that user. For example, a Subject could have a name Principal ("Susan Smith") and a Social Security Number Principal ("987-65-4321"), thereby distinguishing this Subject from other Subjects.

1. package java.security;2. public interface Principal {3. ...4. public String getName();5. }


Obtaining a Specific Principal from a Subject

• Applications (and app. servers) typically adopt a convention stating that the Set of Principals on a Subject can only contain one instance of a particular Principal class.

1. // List the UserPrincipalExample principals2. Set userPrinSet = subject.getPrincipals(UserPrincipalExample.class);3. Iterator userPrinItr = userPrinSet.iterator();4. System.out.println("Found the following UserPrincipalsExample:");5. while (userPrinItr.hasNext()) {6. Principal p = (Principal) userPrinItr.next();7. System.out.println("\t" + p.toString());8. }


Outline

• Introduction• Authentication• Authorization


Authentication Overview1. The application

creates a LoginContext and calls login()

2. The LoginContext looks up the LoginConfiguration to load the predefined LoginModule

3. The LoginContext delegates the authentication to the LoginModules4. The LoginModules use the CallbackHandler to communicate with the

application5. Associate principals and credentials with the Subject if user is authenticated6. Or, throw a LoginException in case the login failed

Authentication Participants

Application

LoginContext

LoginConfiguration

LoginModule

LoginModule

LoginModuleCallback

Handler


Pluggable Authentication Modules

The LoginModule provides authentication via a pluggable module, which implements the authentication algorithm and determines how the authentication is performed

Pluggable Authentication

Login Modules

Application

Login Context

JndiLoginModule

NTLoginModule

UnixLoginModule

Krb5LoginModule

MyLoginModule

LDAP Server

DbLoginModule

NTAuthentication

UnixAuthentication

KerberosAuthentication RDBMS

BiometricAuthentication


LoginConfiguration File

• The default implementation parses a configuration file in the above format

• Configuration file specified via java.security.auth.login.config System parameter

Application1 { ModuleClass Flag ModuleOptions;};Application2 { ModuleClass Flag ModuleOptions; ModuleClass Flag ModuleOptions;};other { ModuleClass Flag ModuleOptions; ModuleClass Flag ModuleOptions;};


Creating a LoginContext

• The name parameter is used to retrieve the appropriate login Configuration

• If a login Configuration with the specified name is not found, a default entry with the name “other” is used. If there is no Configuration with the name “other”, a LoginException is thrown

1. public class LoginContext {2. public LoginContext(String name) { ... }3. public LoginContext(String name, Subject subject) {...}4.5. public LoginContext(String name,6. CallbackHandler handler) { ... }7. public LoginContext(String name, Subject subject,8. CallbackHandler handler) { ... }9.10. ...11.}


Creating a LoginContext (cont.)

• The constructors without a CallbackHandler either:– Rely on the default CallbackHandler specified

in the java.security file under property named auth.login.defaultCallbackHandler

– Do not use a CallbackHandler and rely on the LoginModules to have another means of obtaining the information


Logging In

• Authentication occurs with a call to the login() method

• The login() method invokes the configured LoginModules to perform authentication

• When authentication succeeds, the Subject can be retrieved using the getSubject() method

• The logout() method logs out the Subject and removes its authenticated Principals

1. public class LoginContext {2. ...3. public void login() throws LoginException { }4. public void logout() throws LoginException { }5. public Subject getSubject() { }6. }


LoginModule

• Two-phase authentication:– login() is 1st phase method– commit() and abort() are 2nd phase methods

1. package javax.security.auth.spi;

2. public interface LoginModule {3. public void initialize(Subject subject,4. CallbackHandler callbackHandler,5. Map sharedState,6. Map options);7. public boolean abort() throws LoginException;8. public boolean commit() throws LoginException;9. public boolean login() throws LoginException;10. public boolean logout() throws LoginException;11.}


Login Example: Login Phase

1. // Use the "Example" entry in the login configuration file2. // to authenticate users.3. LoginContext loginContext = null;4. try {5. loginContext = new LoginContext("Example",6. new ExampleCallbackHandler());7. loginContext.login();8. } catch (AccountExpiredException e) {9. ...10.} catch (CredentialExpiredException e) {11. ...12.} catch (FailedLoginException e) {13. ...14.} catch (LoginException e) {15. ...16.} catch (Exception e) {17. ...18.}


Login Example: Commit Phase

• Once the login succeeds we can get the Subject from the LoginContext and get the authenticated Principals from the Subject.

1. // List the Principals the authenticated user has2. Subject subject = loginContext.getSubject();3. Iterator principalItr = subject.getPrincipals().iterator();4. System.out.println("The authenticated user has the " +5. "following Principals:");6. while (principalItr.hasNext()) {7. Principal p = (Principal) principalItr.next();8. System.out.println("\t" + p.toString());9. }


LoginModules in J2SE 1.4

These exist under sun.com.security.auth.module• JndiLoginModule – Authenticates against an

LDAP tree• Krb5LoginModule – Authenticates against a

Kerberos domain• UnixLoginModule – Authenticates against Unix

security• NTLoginModule – Authenticates against NT

security


Callbacks

• javax.security.auth.callback.Callback Marker interface used to indicate a callback.

• Callbacks provide a means for the underlying authentication implementation to communicate with the application and obtains security data such as user name and password as well as provide information such as error and warning messages.

• Included callbacks:– NameCallback– PasswordCallback– TextOutputCallback– TextInputCallback– ChoiceCallback– ConfirmationCallback– LanguageCallback


Custom LoginModule Example

1. public boolean login()2. throws LoginException {3. Callback[] callbacks = new Callback[2];4. callbacks[0] = new NameCallback("userName: ");5. callbacks[1] = new PasswordCallback("password: ",false);6. try {7. callbackHandler.handle(callbacks);8. userName = ((NameCallback) callbacks[0]).getName();9. char[] charPass = ((PasswordCallback) callbacks[1])10. .getPassword();11. if (charPass == null) charPass = new char[0];12. password = new String(charPassword);13. } catch (IOException ioe) {14. ...15. } catch (UnsupportedCallbackException uce) {16. ...17. }18. if (isUserAuthentic()) succeeded = true;19.20. return succeeded;21.}


CallbackHandler

1. package javax.security.auth.callback;

2. public interface CallbackHandler {3. public void handle(Callback[] callbacks)4. throws IOException, UnsupportedCallbackException;5. }


Custom CallbackHandler Example1. public void handle(Callback[] callbacks)2. throws IOException, UnsupportedCallbackException {3. for (int i = 0; i < callbacks.length; i++) {4. if (callbacks[i] instanceof TextOutputCallback) {5. ...6. } else if(callbacks[i] instanceof NameCallback) {7. NameCallback nc = (NameCallback) callbacks[i];8. System.out.print(nc.getPrompt());9. System.out.flush();10. nc.setName(readLine());11. } else if(callbacks[i] instanceof PasswordCallback){12. PasswordCallback pc = (PasswordCallback)13. callbacks[i];14. System.out.print(pc.getPrompt());15. System.out.flush();16. pc.setPassword(readLine().toCharArray());17. } else {18. throw new UnsupportedCallbackException19. (callbacks[i], "Invalid Callback");20. }21. }22.}


Outline

• Introduction• Authentication• Authorization


What is Authorization?

Authorization is the process of determining whether an authenticated user is permitted to perform some actions such as accessing a resource.

The process is Policy based since JAAS is built on the existing Java security model.


CodeSource Based Authorization

• Before the integration of JAAS with Java security, authorization decisions were strictly based on the CodeSource

• A Trusted Library may be given access to sensitive resources while an Applet or another Library may have that access restricted.

Code Source Based Authorization

FileSystem

NetworkSockets

SystemProperties Applet

TrustedLibrary

Library X


CodeSource and Principal Based Authorization

• With the integration of JAAS and J2SE Security, authorization decisions can be made based on the CodeSource and the Principal.

• A Library may not have access privileges to resources when running without a User context or when being executed by User Bart, but when User Andy executes the Library those permissions may be granted.

Code Source and Principal BasedAuthorization

FileSystem

NetworkSockets

SystemProperties

Library X

Andy

Bart


CodeSource & ProtectionDomain

• The CodeSource of a piece of Java code is the URL location that the code was loaded from and the Certificates that we used to sign the code

• The ProtectionDomain is a holder for the CodeSource and a Principal

• Each class is assigned a ProtectionDomain upon being loaded. The Principal is null when the class is first loaded.

ProtectionDomain

CodeSource

CodeSource

URL

Certificate

ProtectionDomain

CodeSource

Principal

Class


AccessControlContext – a Context for Authorization Decisions

• When making access decisions, the security system looks at every ProtectionDomain involved in the call. Access is granted only if every ProtectionDomain in the Context can have access.

Authorization Context

ContextStack Snapshot

AccessController.checkPermission()

java.io.FileInputStream()

java.io.FileReader()

ReadTestFileUseCase.apply()

AuthorizationTestHarness.run()

...

Class

Class

Class

Class

Class

Class

PD

PD

PD

PD

PD

PD

grant codebase "file:./SampleAzn.jar" { permission javax.security.auth.AuthPermission "createLoginContext.Sample";

permission javax.security.auth.AuthPermission "doAsPrivileged"; };


How is JAAS Authorization performed?

To make JAAS authorization take place, the following is required:

• The user must be authenticated• Principal-based entries must be configured in the

security policy. • The Subject that is the result of authentication must

be associated with the current access control context.


Permission

• Permissions represent access to resources.• All Permission object have a name. The

meaning of the name parameter is implementation dependent. Typically the name identifies the resource to be accessed.

1. package java.security;2. public abstract class Permission {3. public Permission (String name) {}4. public abstract boolean implies(Permission p) {}5. public abstract boolean equals(Object o) {}6. public String toString() {}7. public PermissionCollection newPermissionCollection() {}8. }


Policy

• The mapping between PDs and associated Permissions is stored by the Policy

• The grant entry includes all the permissions granted for the principals to do the security sensitive operations, for example, accessing a particular web page or file

Policy Holds a Mapping of ProtectionDomain toPermissions

Policy

ProtectionDomain

ProtectionDomain

ProtectionDomain

PermissionCollection Permission

PermissionPermission






Policy Implementation

• The default implementation of Policy accepts text based configuration in the above format

• Each grant entry is composed of an optional CodeSource, Signers, Principals, and a list of Permissions

• Default security policy is <JRE_HOME>/lib/security/java.policy• Can provide supplemental policy file location via

– -Djava.security.policy=<file> JVM parameter• Can override the default policy file with:

– -Djava.security.policy==<file> JVM parameter

1. grant [CodeBase <URL>,] [Signedby <signers>,]2. [Principal <Principal_Class> <Principal_Name>] {3. Permission <Permission_Class> [<Target_Name>]4. [, <Permission_Actions>]5. [, signedBy <Signer_Name>];6. };


AccessController

• The AccessController embodies the access control algorithm.

• It obtains the current AccessControlContext, which has an array of PDs and then for each PD checks whether the Subject has the requested permission.

Authorization Participants

ProtectionDomain

CodeSource

Principal

PermissionCollection


PermissionPolicy

Class

AccessControlContext

AccessController


Associating a Subject with an Access Control Context

• The doAs method associates the provided Subject with the current access control context and then invokes the run method from the action. The run method implementation contains all the code to be executed as the specified Subject. The action thus executes as the specified Subject.

1. package javax.security.auth;2. public class Subject {3. ...4.5. static public Object doAs(Subject s, PrivilegedAction pa) {}6. static public Object doAs(Subject s, PrivilegedExceptionAction pa){}7. static public Object doAsPrivileged(Subject s,8. PrivilegedAction pa) {}9. static public Object doAsPrivileged(Subject s,10. PrivilegedExceptionAction pa) {}11.}


Execution flow

• Invoke Subject.doAs(..) or Subject.doAsPriviledged()• SecurityManager.checkPermission(..) is called to check

the permission• The SecurityManager delegates the check to the

AccessController• The AccessController tries to find out if the relevant

AccessControlContext contains sufficient permissions for the action to be taken

• If not, the SecurityManager updates the current AccessControlContext with the permissions granted to the subject via the Policy from the Policy file


Execution flow

PrivilegedAction action = new SampleAction(); // The call to Subject.doAsPrivileged is performed via: Subject.doAsPrivileged(mySubject, action, null);

public class SampleAction implements PrivilegedAction { public Object run() { System.out.println("\nYour java.home property value is: " + System.getProperty("java.home")); System.out.println("\nYour user.home property value is: " + System.getProperty("user.home")); File f = new File("foo.txt"); System.out.print("\nfoo.txt does "); if (!f.exists()) System.out.print("not "); System.out.println("exist in the current working directory."); return null; }}


Custom Policy

• Like the LoginModule, the Policy is also a pluggable module. You can hook up other Policy implementations by one of these means:– At runtime by calling Policy.setPolicy()– By changing the value of policy.provider property in

<JRE_HOME>/lib/security/java.security• The specified class name must point to a subclass of

Policy• The specified class must be in the boot classpath• Example included (you must change the java.security

property on your JRE)


Extend JAAS

• JAAS is built on top of the existing Java security model, which is CodeSource based, and the plaintext format policy implementation.

• For an enterprise application you may want to use custom security repositories with JAAS, such as LDAP, database or another file system

• This can be done by writing a customized module thanks to the JAAS pluggable feature


About the Speaker

Speaker is a Senior Architect at Ventyx Inc. He has over 5 years of experience in J2EE/Web development and has worked with extensive open source technologies. His interests are in the areas of technical architecture, enterprise application integration and web services.

Business

Developing With JAAS