JAAS Cheat Sheet

Revision as of 19:27, 8 May 2012 by Jmanico (talk | contribs) (Execution syntax)

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What is JAAS authentication

The process of verifying the identity of a user or another system is authentication. JAAS, as an authentication framework manages the authenticated user’s identity and credentials from login to logout.

The JAAS authentication lifecycle:

  1. Create LoginContext
  2. Read the configuration file for one or more LoginModules to initialize
  3. Call LoginContext.initialize () for each LoginModule to initialize.
  4. Call LoginContext.login () for each LoginModule
  5. If login successful then call LoginContext.commit () else call LoginContext.abort ()

Configuration file

The JAAS configuration file contains a LoginModule stanza for each LoginModule available for logging on to the application.

A stanza from a JAAS configuration file:

     USNavy.AppLoginModule required

Note the placement of the semicolons, terminating both LoginModule entries and stanzas. The word required indicates the LoginContext’s login () method must be successful when logging in the user. The LoginModule-specific values debug and succeeded are passed to the LoginModule. They are defined by the LoginModule and their usage is managed inside the LoginModule. Note, Options are Configured using key-value pairing such as debug="true" and the key and value should be separated by a 'equals' sign.

Main.java (The client)

Execution syntax

                Java –Djava.security.auth.login.config==packageName/packageName.config 
                           packageName.Main Stanza1
               packageName is the directory containing the config file.
               packageName.config specifies the config file in the Java package, packageName
               packageName.Main specifies Main.java in the Java package, packageName                                       
               Stanza1 is the name of the stanza Main () should read from the config file.
  • When executed, the 1st command line argument is the stanza from the config file. The Stanza names the LoginModule to be used. The 2nd argument is the CallbackHandler.
  • Create a new LoginContext with the arguments passed to Main.java.
    • loginContext = new LoginContext (args[0], new AppCallbackHandler ());
  • Call the LoginContext.Login Module
    • loginContext.login ();
  • The value in succeeded Option is returned from loginContext.login ()
* If the login was successful, a subject was created.


    • A LoginModule must have the following authentication methods:
        initialize ()
        login ()
        commit ()
        abort ()
        logout () 
        • initialize ()
              • In Main (), after the LoginContext reads the correct stanza from the config file, the 
                 LoginContext instantiates the LoginModule specified in the stanza.
              • initialize () methods signature: 
                        Public void initialize (Subject subject, CallbackHandler callbackHandler, Map 
                                                               sharedState, Map options) 
               • The arguments above should be saved as follows:
                        this.subject = subject;
                        this.callbackHandler = callbackHandler;
                        this.sharedState = sharedState;
                        this.options = options;  
              • What the initialize () method does:
                 • Builds a subject object of the Subject class contingent on a successful login ()
                 • Sets the CallbackHandler which interacts with the user to gather login information
                 • If a LoginContext specifies 2 or more LoginModules, which is legal, they can share 
                    information via a sharedState map
                 • Saves state information such as debug and succeeded in an options Map     
         • login ()
               • Captures user supplied login information.  The code snippet below declares an array 
                  of two callback objects which, when passed to the callbackHandler.handle method in 
                  the callbackHandler.java program, will be loaded with a user name and password 
                  provided interactively by the user. 
                         Callback[] callbacks = new Callback [2];
                           callbacks[0] = new NameCallback (“name”); 
                           callbacks[1] = new PasswordCallback (“password”, false);
                         callbackHandler.handle (callbacks);
               • Authenticates the user
               • Retrieves the user supplied information from the callback objects:
                          String ID = nameCallback.getName ();
                          char[] tempPW = passwordCallback.getPassword ();
               • Compare name and tempPW to values stored in a repository such as LDAP
               • Set the value of the variable succeeded and return to Main ()
        • commit ()
             • Once the users credentials are successfully verified during login (), the JAAS 
                authentication framework associates the credentials, as needed, with the 
                subject. There are two types of credentials, public and private.  Public credentials 
                include public keys.  Private credentials include passwords and public keys.  
                Principals (i.e. Identities the subject has other than their login name) 
                such as employee number or membership ID in a user group are added to the 
             • Code snippet setting then adding a principal and two credentials to a subject:
                        private Principal PR1 = new DemoPrincipal(“Quarterback”);
                        private String publicCredential = “Aikman”;
                        private String privateCredential = “Secret database accessible only password”;
                        Set principalSet = subject.getPrincipals();
                        principalSet.add (PR1);
     • abort ()
          • The abort () method is called when authentication doesn’t succeed.  Before the abort () 
             method exits the LoginModule, care should be taken to reset state including the user 
             name and password input fields.  
• logout ()
          • The arguments above should be saved as follows:
                        Set principalSet = subject.getPrincipals ();
                        principalSet.remove (PR1);
• CallbackHandler.java
      • The callbackHandler is in a source (.java) file separate from any single LoginModule 
         so that it can service a multitude of LoginModules with differing callback objects.
      • Creates instance of the CallbackHandler class and has only one method, handle ().
      • A CallbackHandler servicing a LoginModule requiring username & password to login:  
               public void handle(Callback[] callbacks) { 
               for (int i = 0; i < callbacks.length; i++) {
                   Callback callback = callbacks[i];
                   if (callback instanceof NameCallback) {
                       NameCallback nameCallBack = (NameCallback) callback; 
                   }  else if (callback instanceof PasswordCallback) {
                       PasswordCallback passwordCallBack = (PasswordCallback) callback;

Authors and Primary Editors Dr. A.L. Gottlieb – AnthonyG [at] owasp dot org