JAAS Authentication Tutorial

The Authentication Tutorial Code

The code for this tutorial consists of three files:

SampleAcn.java contains the sample application class (SampleAcn) and another class used to handle user input (MyCallbackHandler). The code in this file is the only code you need to understand for this tutorial. Your application will only indirectly use the other source files.
SampleLoginModule.java is the class specified by the tutorial's login configuration file, sample_jass.config, described in The Login Configuration File for the JAAS Authentication Tutorial 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 java.security.Principal interface. It is used by SampleLoginModule.

SampleAcn.java

Our authentication tutorial application code is contained in a single source file, SampleAcn.java. That file contains two classes:

The SampleAcn Class

The main method of the SampleAcn class performs the authentication and then reports whether or not authentication succeeded.

The code for authenticating the user is very simple, consisting of just two steps:

First the basic code is shown, followed by The Complete SampleAcn Class Code, complete with the import statement it requires and error handling.

Instantiating a LoginContext

In order to authenticate a user, you first need a javax.security.auth.login.LoginContext. Here is the basic way to instantiate a LoginContext:


import javax.security.auth.login.*;
. . .
LoginContext lc =
    new LoginContext(<config file entry name>,
           <CallbackHandler to be used for user interaction>);

and here is the specific way our tutorial code does the instantiation:


import javax.security.auth.login.*;
. . .
LoginContext lc =
    new LoginContext("Sample",
          new MyCallbackHandler());

The arguments are the following:

The name of an entry in the JAAS login configuration file
This is the name for the LoginContext to use to look up an entry for this application in the JAAS login configuration file, described in The Login Configuration. Such an entry specifies the class(es) that implement the desired underlying authentication technology(ies). The class(es) must implement the LoginModule interface, which is in the javax.security.auth.spi package.

In our sample code, we use the SampleLoginModule supplied with this tutorial. The SampleLoginModule performs authentication by ensuring that the user types a particular name and password.

The entry in the login configuration file we use for this tutorial, sample_jass.config (see The Login Configuration File for the JAAS Authentication Tutorial), has the name "Sample", so that is the name we specify as the first argument to the LoginContext constructor.
A CallbackHandler instance
When a LoginModule needs to communicate with the user, for example to ask for a user name and password, it does not do so directly. That is because there are various ways of communicating with a user, and it is desirable for LoginModules to remain independent of the different types of user interaction. Rather, the LoginModule invokes a javax.security.auth.callback.CallbackHandler to perform the user interaction and obtain the requested information, such as the user name and password.

An instance of the particular CallbackHandler to be used is specified as the second argument to the LoginContext constructor. The LoginContext forwards that instance to the underlying LoginModule (in our case SampleLoginModule). An application typically provides its own CallbackHandler implementation. A simple CallbackHandler, TextCallbackHandler, is provided in the com.sun.security.auth.callback package to output information to and read input from the command line. However, we instead demonstrate the more typical case of an application providing its own CallbackHandler implementation, described in The MyCallbackHandler Class.

Calling the LoginContext's login Method

Once we have a LoginContext lc, we can call its login method to carry out the authentication process:

lc.login();

The LoginContext instantiates a new empty javax.security.auth.Subject object (which represents the user or service being authenticated; see Subject). The LoginContext constructs the configured LoginModule (in our case SampleLoginModule) and initializes it with this new Subject and MyCallbackHandler.

The LoginContext's login method then calls methods in the SampleLoginModule to perform the login and authentication. The SampleLoginModule will utilize the MyCallbackHandler to obtain the user name and password. Then the SampleLoginModule will check that the name and password are the ones it expects.

If authentication is successful, the SampleLoginModule populates the Subject with a Principal representing the user. The Principal the SampleLoginModule places in the Subject is an instance of SamplePrincipal, which is a sample class implementing the java.security.Principal interface.

The calling application can subsequently retrieve the authenticated Subject by calling the LoginContext's getSubject method, although doing so is not necessary for this tutorial.

The Complete SampleAcn Class Code

Now that you have seen the basic code required to authenticate the user, we can put it all together into the full class in SampleAcn.java, which includes relevant import statements and error handling:

SampleAcn.java

package sample;

import java.io.*;
import java.util.*;
import javax.security.auth.login.*;
import javax.security.auth.*;
import javax.security.auth.callback.*;

/**
 * This Sample application attempts to authenticate a user
 * and reports whether or not the authentication was successful.
 */
public class SampleAcn {

   /**
    * Attempt to authenticate the user.
    *
    * @param args input arguments for this application.  These are ignored.
    */
    public static void main(String[] args) {

        // Obtain a LoginContext, needed for authentication. Tell it
        // to use the LoginModule implementation specified by the
        // entry named "Sample" in the JAAS login configuration
        // file and to also use the specified CallbackHandler.
        LoginContext lc = null;
        try {
            lc = new LoginContext("Sample", new MyCallbackHandler());
        } catch (LoginException le) {
            System.err.println("Cannot create LoginContext. "
                + le.getMessage());
            System.exit(-1);
        } catch (SecurityException se) {
            System.err.println("Cannot create LoginContext. "
                + se.getMessage());
            System.exit(-1);
        }

        // the user has 3 attempts to authenticate successfully
        int i;
        for (i = 0; i < 3; i++) {
            try {

                // attempt authentication
                lc.login();

                // if we return with no exception, authentication succeeded
                break;

            } catch (LoginException le) {

                  System.err.println("Authentication failed:");
                  System.err.println("  " + le.getMessage());
                  try {
                      Thread.currentThread().sleep(3000);
                  } catch (Exception e) {
                      // ignore
                  }

            }
        }

        // did they fail three times?
        if (i == 3) {
            System.out.println("Sorry");
            System.exit(-1);
        }

        System.out.println("Authentication succeeded!");

    }
}


/**
 * The application implements the CallbackHandler.
 *
 * <p> This application is text-based.  Therefore it displays information
 * to the user using the OutputStreams System.out and System.err,
 * and gathers input from the user using the InputStream System.in.
 */
class MyCallbackHandler implements CallbackHandler {

    /**
     * Invoke an array of Callbacks.
     *
     * <p>
     *
     * @param callbacks an array of <code>Callback</code> objects which contain
     *                  the information requested by an underlying security
     *                  service to be retrieved or displayed.
     *
     * @exception java.io.IOException if an input or output error occurs. <p>
     *
     * @exception UnsupportedCallbackException if the implementation of this
     *                  method does not support one or more of the Callbacks
     *                  specified in the <code>callbacks</code> parameter.
     */
    public void handle(Callback[] callbacks)
    throws IOException, UnsupportedCallbackException {

        for (int i = 0; i < callbacks.length; i++) {
            if (callbacks[i] instanceof TextOutputCallback) {

                // display the message according to the specified type
                TextOutputCallback toc = (TextOutputCallback)callbacks[i];
                switch (toc.getMessageType()) {
                case TextOutputCallback.INFORMATION:
                    System.out.println(toc.getMessage());
                    break;
                case TextOutputCallback.ERROR:
                    System.out.println("ERROR: " + toc.getMessage());
                    break;
                case TextOutputCallback.WARNING:
                    System.out.println("WARNING: " + toc.getMessage());
                    break;
                default:
                    throw new IOException("Unsupported message type: " +
                                        toc.getMessageType());
                }

            } else if (callbacks[i] instanceof NameCallback) {

                // prompt the user for a username
                NameCallback nc = (NameCallback)callbacks[i];

                System.err.print(nc.getPrompt());
                System.err.flush();
                nc.setName((new BufferedReader
                        (new InputStreamReader(System.in))).readLine());

            } else if (callbacks[i] instanceof PasswordCallback) {

                // prompt the user for sensitive information
                PasswordCallback pc = (PasswordCallback)callbacks[i];
                System.err.print(pc.getPrompt());
                System.err.flush();
                pc.setPassword(System.console().readPassword());

            } else {
                throw new UnsupportedCallbackException
                        (callbacks[i], "Unrecognized Callback");
            }
        }
    }
}

The MyCallbackHandler Class

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. An application can either use one of the sample implementations provided in the com.sun.security.auth.callback package or, more typically, write a CallbackHandler implementation. The application passes the CallbackHandler as an argument to the LoginContext instantiation. The LoginContext forwards the CallbackHandler directly to the underlying LoginModules.

The tutorial sample code supplies its own CallbackHandler implementation, the MyCallbackHandler class in .

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 javax.security.auth.callback.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.

The MyCallbackHandler handle method is structured as follows:

public void handle(Callback[] callbacks)
  throws IOException, UnsupportedCallbackException {

  for (int i = 0; i < callbacks.length; i++) {
    if (callbacks[i] instanceof TextOutputCallback) {

      // display a message according to a specified type
      . . .

    } else if (callbacks[i] instanceof NameCallback) {

      // prompt the user for a username
      . . .

    } else if (callbacks[i] instanceof PasswordCallback) {

      // prompt the user for a password
      . . .

    } else {
        throw new UnsupportedCallbackException
         (callbacks[i], "Unrecognized Callback");
    }
  }
}

A CallbackHandler handle method is passed an array of Callback instances, each of a particular type (NameCallback, PasswordCallback, etc.). It must handle each Callback, performing user interaction in a way that is appropriate for the executing application.

MyCallbackHandler handles three types of Callbacks: NameCallback to prompt the user for a user name, PasswordCallback to prompt for a password, and TextOutputCallback to report any error, warning, or other messages the SampleLoginModule wishes to send to the user.

The handle method handles a TextOutputCallback by extracting the message to be reported and then printing it to System.out, optionally preceded by additional wording that depends on the message type. The message to be reported is determined by calling the TextOutputCallback's getMessage method and the type by calling its getMessageType method. Here is the code for handling a TextOutputCallback:

if (callbacks[i] instanceof TextOutputCallback) {

  // display the message according to the specified type
  TextOutputCallback toc = (TextOutputCallback)callbacks[i];
  switch (toc.getMessageType()) {
     case TextOutputCallback.INFORMATION:
        System.out.println(toc.getMessage());
        break;
     case TextOutputCallback.ERROR:
        System.out.println("ERROR: " + toc.getMessage());
        break;
     case TextOutputCallback.WARNING:
        System.out.println("WARNING: " + toc.getMessage());
        break;
     default:
        throw new IOException("Unsupported message type: " +
            toc.getMessageType());
   }

The handle method handles a NameCallback by prompting the user for a user name. It does this by printing the prompt to System.err. It then sets the name for use by the SampleLoginModule by calling the NameCallback's setName method, passing it the name typed by the user:

} else if (callbacks[i] instanceof NameCallback) {

    // prompt the user for a username
    NameCallback nc = (NameCallback)callbacks[i];

    System.err.print(nc.getPrompt());
    System.err.flush();
    nc.setName((new BufferedReader
        (new InputStreamReader(System.in))).readLine());

Similarly, the handle method handles a PasswordCallback by printing a prompt to System.err to prompt the user for a password. It then sets the password for use by the SampleLoginModule by calling the PasswordCallback's setPassword method, passing it the password typed by the user:

} else if (callbacks[i] instanceof PasswordCallback) {

    // prompt the user for sensitive information
    PasswordCallback pc = (PasswordCallback)callbacks[i];

    System.err.print(pc.getPrompt());
    System.err.flush();
    pc.setPassword(System.console().readPassword());

SampleLoginModule.java and SamplePrincipal.java

SampleLoginModule.java implements the LoginModule interface. SampleLoginModule is the class specified by the tutorial's login configuration file (see The Login Configuration File for the JAAS Authentication Tutorial) 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. This SampleLoginModule is specified by the tutorial's login configuration file as the LoginModule to use because (1) It performs a basic type of authentication suitable for any environment and thus is appropriate for a tutorial for all users, and (2) It provides an example LoginModule implementation for experienced programmers who require the ability to write a LoginModule implementing an authentication technology.

SamplePrincipal.java is a sample class implementing the java.security.Principal interface. If authentication is successful, the SampleLoginModule populates a Subject with a SamplePrincipal representing the user.

Important: If you are an application writer, you do not need to know how to write a LoginModule or a Principal implementation. You do not need to examine the SampleLoginModule or SamplePrincipal code. 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. You need to determine which LoginModule(s) you want to use and read the LoginModule's documentation to learn about what options you can specify values for (in the configuration) to control the LoginModule's behavior.

Any vendor can provide a LoginModule implementation that you can use. Some implementations are supplied with the JDK from Oracle, as listed in Appendix B: JAAS Login Configuration File.

Information for programmers who want to write a LoginModule can be found in Java Authentication and Authorization Service (JAAS): LoginModule Developer's Guide.

SampleLoginModule.java

package sample.module;

import java.util.*;
import java.io.IOException;
import javax.security.auth.*;
import javax.security.auth.callback.*;
import javax.security.auth.login.*;
import javax.security.auth.spi.*;
import sample.principal.SamplePrincipal;

/**
 * <p> This sample LoginModule authenticates users with a password.
 *
 * <p> This LoginModule only recognizes one user:       testUser
 * <p> testUser's password is:  testPassword
 *
 * <p> If testUser successfully authenticates itself,
 * a <code>SamplePrincipal</code> with the testUser's user name
 * is added to the Subject.
 *
 * <p> This LoginModule recognizes the debug option.
 * If set to true in the login Configuration,
 * debug messages will be output to the output stream, System.out.
 *
 */
public class SampleLoginModule implements LoginModule {

    // initial state
    private Subject subject;
    private CallbackHandler callbackHandler;
    private Map sharedState;
    private Map options;

    // configurable option
    private boolean debug = false;

    // the authentication status
    private boolean succeeded = false;
    private boolean commitSucceeded = false;

    // username and password
    private String username;
    private char[] password;

    // testUser's SamplePrincipal
    private SamplePrincipal userPrincipal;

    /**
     * Initialize this <code>LoginModule</code>.
     *
     * @param subject the <code>Subject</code> to be authenticated. <p>
     *
     * @param callbackHandler a <code>CallbackHandler</code> for communicating
     *                  with the end user (prompting for user names and
     *                  passwords, for example). <p>
     *
     * @param sharedState shared <code>LoginModule</code> state. <p>
     *
     * @param options options specified in the login
     *                  <code>Configuration</code> for this particular
     *                  <code>LoginModule</code>.
     */
    public void initialize(Subject subject,
                   CallbackHandler callbackHandler,
                         Map<java.lang.String, ?> sharedState,
                         Map<java.lang.String, ?> options) {

        this.subject = subject;
        this.callbackHandler = callbackHandler;
        this.sharedState = sharedState;
        this.options = options;

        // initialize any configured options
        debug = "true".equalsIgnoreCase((String)options.get("debug"));
    }

    /**
     * Authenticate the user by prompting for a user name and password.
     *
     * @return true in all cases since this <code>LoginModule</code>
     *          should not be ignored.
     *
     * @exception FailedLoginException if the authentication fails. <p>
     *
     * @exception LoginException if this <code>LoginModule</code>
     *          is unable to perform the authentication.
     */
    public boolean login() throws LoginException {

        // prompt for a user name and password
        if (callbackHandler == null)
            throw new LoginException("Error: no CallbackHandler available " +
                        "to garner authentication information from the user");

        Callback[] callbacks = new Callback[2];
        callbacks[0] = new NameCallback("user name: ");
        callbacks[1] = new PasswordCallback("password: ", false);

        try {
            callbackHandler.handle(callbacks);
            username = ((NameCallback)callbacks[0]).getName();
            char[] tmpPassword = ((PasswordCallback)callbacks[1]).getPassword();
            if (tmpPassword == null) {
                // treat a NULL password as an empty password
                tmpPassword = new char[0];
            }
            password = new char[tmpPassword.length];
            System.arraycopy(tmpPassword, 0,
                        password, 0, tmpPassword.length);
            ((PasswordCallback)callbacks[1]).clearPassword();

        } catch (java.io.IOException ioe) {
            throw new LoginException(ioe.toString());
        } catch (UnsupportedCallbackException uce) {
            throw new LoginException("Error: " + uce.getCallback().toString() +
                " not available to garner authentication information " +
                "from the user");
        }

        // print debugging information
        if (debug) {
            System.out.println("\t\t[SampleLoginModule] " +
                                "user entered user name: " +
                                username);
            System.out.print("\t\t[SampleLoginModule] " +
                                "user entered password: ");
            for (int i = 0; i < password.length; i++)
                System.out.print(password[i]);
            System.out.println();
        }

        // verify the username/password
        boolean usernameCorrect = false;
        boolean passwordCorrect = false;
        if (username.equals("testUser"))
            usernameCorrect = true;
        if (usernameCorrect &&
            password.length == 12 &&
            password[0] == 't' &&
            password[1] == 'e' &&
            password[2] == 's' &&
            password[3] == 't' &&
            password[4] == 'P' &&
            password[5] == 'a' &&
            password[6] == 's' &&
            password[7] == 's' &&
            password[8] == 'w' &&
            password[9] == 'o' &&
            password[10] == 'r' &&
            password[11] == 'd') {

            // authentication succeeded!!!
            passwordCorrect = true;
            if (debug)
                System.out.println("\t\t[SampleLoginModule] " +
                                "authentication succeeded");
            succeeded = true;
            return true;
        } else {

            // authentication failed -- clean out state
            if (debug)
                System.out.println("\t\t[SampleLoginModule] " +
                                "authentication failed");
            succeeded = false;
            username = null;
            for (int i = 0; i < password.length; i++)
                password[i] = ' ';
            password = null;
            if (!usernameCorrect) {
                throw new FailedLoginException("User Name Incorrect");
            } else {
                throw new FailedLoginException("Password Incorrect");
            }
        }
    }

    /**
     * This method is called if the LoginContext's
     * overall authentication succeeded
     * (the relevant REQUIRED, REQUISITE, SUFFICIENT and OPTIONAL LoginModules
     * succeeded).
     *
     * If this LoginModule's own authentication attempt
     * succeeded (checked by retrieving the private state saved by the
     * <code>login</code> method), then this method associates a
     * <code>SamplePrincipal</code>
     * with the <code>Subject</code> located in the
     * <code>LoginModule</code>.  If this LoginModule's own
     * authentication attempted failed, then this method removes
     * any state that was originally saved.
     *
     * @exception LoginException if the commit fails.
     *
     * @return true if this LoginModule's own login and commit
     *          attempts succeeded, or false otherwise.
     */
    public boolean commit() throws LoginException {
        if (succeeded == false) {
            return false;
        } else {
            // add a Principal (authenticated identity)
            // to the Subject

            // assume the user we authenticated is the SamplePrincipal
            userPrincipal = new SamplePrincipal(username);
            if (!subject.getPrincipals().contains(userPrincipal))
                subject.getPrincipals().add(userPrincipal);

            if (debug) {
                System.out.println("\t\t[SampleLoginModule] " +
                                "added SamplePrincipal to Subject");
            }

            // in any case, clean out state
            username = null;
            for (int i = 0; i < password.length; i++)
                password[i] = ' ';
            password = null;

            commitSucceeded = true;
            return true;
        }
    }

    /**
     * This method is called if the LoginContext's
     * overall authentication failed.
     * (the relevant REQUIRED, REQUISITE, SUFFICIENT and OPTIONAL LoginModules
     * did not succeed).
     *
     * If this LoginModule's own authentication attempt
     * succeeded (checked by retrieving the private state saved by the
     * <code>login</code> and <code>commit</code> methods),
     * then this method cleans up any state that was originally saved.
     *
     * @exception LoginException if the abort fails.
     *
     * @return false if this LoginModule's own login and/or commit attempts
     *          failed, and true otherwise.
     */
    public boolean abort() throws LoginException {
        if (succeeded == false) {
            return false;
        } else if (succeeded == true && commitSucceeded == false) {
            // login succeeded but overall authentication failed
            succeeded = false;
            username = null;
            if (password != null) {
                for (int i = 0; i < password.length; i++)
                    password[i] = ' ';
                password = null;
            }
            userPrincipal = null;
        } else {
            // overall authentication succeeded and commit succeeded,
            // but someone else's commit failed
            logout();
        }
        return true;
    }

    /**
     * Logout the user.
     *
     * This method removes the <code>SamplePrincipal</code>
     * that was added by the <code>commit</code> method.
     *
     * @exception LoginException if the logout fails.
     *
     * @return true in all cases since this <code>LoginModule</code>
     *          should not be ignored.
     */
    public boolean logout() throws LoginException {

        subject.getPrincipals().remove(userPrincipal);
        succeeded = false;
        succeeded = commitSucceeded;
        username = null;
        if (password != null) {
            for (int i = 0; i < password.length; i++)
                password[i] = ' ';
            password = null;
        }
        userPrincipal = null;
        return true;
    }
}

SamplePrincipal.java

package sample.principal;

import java.security.Principal;

/**
 * This class implements the <code>Principal</code> interface
 * and represents a Sample user.
 *
 * Principals such as this <code>SamplePrincipal</code>
 * may be associated with a particular <code>Subject</code>
 * to augment that <code>Subject</code> with an additional
 * identity.  Refer to the <code>Subject</code> class for more information
 * on how to achieve this.  Authorization decisions can then be based upon
 * the Principals associated with a <code>Subject</code>.
 *
 * @see java.security.Principal
 * @see javax.security.auth.Subject
 */
public class SamplePrincipal implements Principal, java.io.Serializable {

    /**
     * @serial
     */
    private String name;

    /**
     * Create a SamplePrincipal with a Sample username.
     *
     * @param name the Sample username for this user.
     *
     * @exception NullPointerException if the <code>name</code>
     *                  is <code>null</code>.
     */
    public SamplePrincipal(String name) {
        if (name == null)
            throw new NullPointerException("illegal null input");

        this.name = name;
    }

    /**
     * Return the Sample username for this <code>SamplePrincipal</code>.
     *
     * @return the Sample username for this <code>SamplePrincipal</code>
     */
    public String getName() {
        return name;
    }

    /**
     * Return a string representation of this <code>SamplePrincipal</code>.
     *
     * @return a string representation of this <code>SamplePrincipal</code>.
     */
    public String toString() {
        return("SamplePrincipal:  " + name);
    }

    /**
     * Compares the specified Object with this <code>SamplePrincipal</code>
     * for equality.  Returns true if the given object is also a
     * <code>SamplePrincipal</code> and the two SamplePrincipals
     * have the same username.
     *
     * @param o Object to be compared for equality with this
     *          <code>SamplePrincipal</code>.
     *
     * @return true if the specified Object is equal equal to this
     *          <code>SamplePrincipal</code>.
     */
    public boolean equals(Object o) {
        if (o == null)
            return false;

        if (this == o)
            return true;

        if (!(o instanceof SamplePrincipal))
            return false;
        SamplePrincipal that = (SamplePrincipal)o;

        if (this.getName().equals(that.getName()))
            return true;
        return false;
    }

    /**
     * Return a hash code for this <code>SamplePrincipal</code>.
     *
     * @return a hash code for this <code>SamplePrincipal</code>.
     */
    public int hashCode() {
        return name.hashCode();
    }
}

The Login Configuration

JAAS authentication is performed in a pluggable fashion, so applications can remain independent from underlying authentication technologies. A system administrator determines the authentication technologies, or LoginModules, to be used for each application and configures them in a login Configuration. The source of the configuration information (for example, a file or a database) is up to the current javax.security.auth.login.Configuration implementation. The default Configuration implementation from Oracle reads configuration information from configuration files, as described in the ConfigFile class.

See Appendix B: JAAS Login Configuration File for information as to what a login configuration file is, what it contains, and how to specify which login configuration file should be used.

The Login Configuration File for the JAAS Authentication Tutorial

As noted, the login configuration file we use for this tutorial, sample_jass.config, contains just one entry, which is

Sample {
  sample.module.SampleLoginModule required debug=true;
};

This entry is named "Sample" and that is the name that our tutorial application, SampleAcn, uses to refer to this entry. The entry specifies that the LoginModule to be used to do the user authentication is the SampleLoginModule in the sample.module package and that this SampleLoginModule is required to "succeed" in order for authentication to be considered successful. The SampleLoginModule succeeds only if the name and password supplied by the user are the one it expects ("testUser" and "testPassword", respectively).

The SampleLoginModule also defines a "debug" option that can be set to true as shown. If this option is set to true, SampleLoginModule outputs extra information about the progress of authentication. A LoginModule can define as many options as it wants. The LoginModule documentation should specify the possible option names and values you can set in your configuration file.

Running the Code

To execute our JAAS authentication tutorial code, all you have to do is

Place the following file into a directory:
- sample_jass.config login configuration file (see The Login Configuration File for the JAAS Authentication Tutorial)
Create a subdirectory named sample of that top-level directory, and place the following into it (note the SampleAcn and MyCallbackHandler classes, both in SampleAcn.java, are in a package named sample):
- SampleAcn.java application source file
Create a subdirectory of the sample directory and name it module. Place the following into it (note the SampleLoginModule class is in a package named sample.module):
- SampleLoginModule.java source file
Create another subdirectory of the sample directory and name it principal. Place the following into it (note the SamplePrincipal class is in a package named sample.principal):
- SamplePrincipal.java source file
While in the top-level directory, compile SampleAcn.java, SampleLoginModule.java, and SamplePrincipal.java:

javac sample/SampleAcn.java sample/module/SampleLoginModule.java sample/principal/SamplePrincipal.java

(Type all that on one line.)
Execute the SampleAcn application, specifying
- by -Djava.security.auth.login.config==sample_jaas.config that the login configuration file to be used is sample_jaas.config.

The following is the full command:

java -Djava.security.auth.login.config==sample_jaas.config sample.SampleAcn

Note:

If you use a single equals sign (=) with the java.security.auth.login.config system property (instead of a double equals sign (==)), then the configurations specified by both this system property and the java.security file are used.

You will be prompted for your user name and password, and the SampleLoginModule specified in the login configuration file will check to ensure these are correct. The SampleLoginModule expects testUser for the user name and testPassword for the password.

You will see some messages output by SampleLoginModule as a result of the debug option being set to true in the login configuration file. Then, if your login is successful, you will see the following message output by SampleAcn:

Authentication succeeded!

If the login is not successful (for example, if you misspell the password), you will see

Authentication failed:

followed by a reason for the failure. For example, if you mistype the password, you may see a message like the following:

Authentication failed:
  Password Incorrect

SampleAcn gives you three chances to successfully log in.

Running the Code with a Security Manager

When a Java program is run with a security manager installed, the program is not allowed to access resources or otherwise perform security-sensitive operations unless it is explicitly granted permission to do so by the security policy in effect. (See Permissions in the JDK.) The permission must be granted by an entry in a policy file (see Default Policy Implementation and Policy File Syntax.)

WARNING:

The Security Manager and APIs related to it have been deprecated and are subject to removal in a future release. There is no replacement for the Security Manager. See JEP 411 for discussion and alternatives.

Most browsers install a security manager, so applets typically run under the scrutiny of a security manager. Applications, on the other hand, do not, since a security manager is not automatically installed when an application is running. Thus an application, like our SampleAcn application, by default has full access to resources.

To run an application with a security manager, simply invoke the interpreter with a -Djava.security.manager argument included on the command line.

If you try invoking SampleAcn with a security manager but without specifying any policy file, you will get the following (unless you have a default policy setup elsewhere that grants the required permissions or grants AllPermission):

% java -Djava.security.manager \
 -Djava.security.auth.login.config==sample_jaas.config sample.SampleAcn
Exception in thread "main" java.security.AccessControlException:
  access denied (
  javax.security.auth.AuthPermission createLoginContext.Sample)

As you can see, you get an AccessControlException, because we haven't created and used a policy file granting our code the permission that is required in order to be allowed to create a LoginContext.

Here are the complete steps required in order to be able to run our SampleAcn application with a security manager installed. You can skip the first five steps if you have already done them, as described in Running the Code.

Place the following file into a directory:
- sample_jass.config login configuration file (see The Login Configuration File for the JAAS Authentication Tutorial)
Create a subdirectory named sample of that top-level directory, and place the following into it (note the SampleAcn and MyCallbackHandler classes, both in SampleAcn.java, are in a package named sample):
- SampleAcn.java application source file
Create a subdirectory of the sample directory and name it module. Place the following into it (note the SampleLoginModule class is in a package named sample.module):
- SampleLoginModule.java source file
Create another subdirectory of the sample directory and name it principal. Place the following into it (note the SamplePrincipal class is in a package named sample.principal):
- SamplePrincipal.java source file
While in the top-level directory, compile SampleAcn.java, SampleLoginModule.java, and SamplePrincipal.java:

javac sample/SampleAcn.java sample/module/SampleLoginModule.java sample/principal/SamplePrincipal.java

(Type all that on one line.)
Create a JAR file containing SampleAcn.class and MyCallbackHandler.class:

jar -cvf SampleAcn.jar sample/SampleAcn.class sample/MyCallbackHandler.class

(Type all that on one line.) This command creates a JAR file, SampleAcn.jar, and places the SampleAcn.class and MyCallbackHandler.class files inside it.
Create a JAR file containing SampleLoginModule.class and SamplePrincipal.class:

jar -cvf SampleLM.jar sample/module/SampleLoginModule.class sample/principal/SamplePrincipal.class
Create a policy file granting the required permissions.

The permission that is needed by code attempting to instantiate a LoginContext is a javax.security.auth.AuthPermission with target createLoginContext.<entry name>. Here, <entry name> refers to the name of the login configuration file entry that the application references in its instantiation of LoginContext. The name used by our SampleAcn application's LoginContext instantiation is Sample, as you can see in the code:
```
LoginContext lc =
    new LoginContext("Sample",
          new MyCallbackHandler());
```
Thus, the permission that needs to be granted to SampleAcn.jar is
```
permission javax.security.auth.AuthPermission
  "createLoginContext.Sample";
```
The SampleLM.jar file also needs to be granted a permission. The documentation for a LoginModule should tell you what permissions it needs to be granted. In the case of SampleLoginModule, it needs a javax.security.auth.AuthPermission with target modifyPrincipals in order to populate a Subject with a Principal:
```
permission javax.security.auth.AuthPermission
  "modifyPrincipals";
```
Copy the policy file sampleacn.policy to the same directory as that in which you stored SampleAcn.java, etc. The policy file contains the following grant statement to grant SampleAcn.jar (in the current directory) its required permission:
```
grant codebase "file:./SampleAcn.jar" {
   permission javax.security.auth.AuthPermission "createLoginContext.Sample";
};
```
The policy file also contains the following grant statement to grant SampleLM.jar (also in the current directory) its required permission:
```
grant codebase "file:./SampleLM.jar" {
   permission javax.security.auth.AuthPermission "modifyPrincipals";
};
```
Note: Policy files and the structure of entries within them are described in Default Policy Implementation and Policy File Syntax. Permissions are described in Permissions in the JDK.

Execute the SampleAcn application, specifying
1. by an appropriate -classpath clause that classes should be searched for in the SampleAcn.jar and SampleLM.jar JAR files,
2. by -Djava.security.manager that a security manager should be installed,
3. by -Djava.security.policy==sampleacn.policy that the policy file to be used is sampleacn.policy, and
4. by -Djava.security.auth.login.config==sample_jaas.config that the login configuration file to be used is sample_jaas.config.
Note:

Use the double equals sign (==) with the java.security.policy property with care as it overrides the built-in JDK policy file, which grants a set of default permissions that are designed to provide a secure, out-of-the-box configuration for the JDK. Overriding this policy may result in unexpected behavior (JDK code may not be granted the right permissions) and should only be done by experienced users.

If you use a single equals sign (=) with the java.security.auth.login.config system property (instead of a double equals sign (==)), then the configurations specified by both this system property and the java.security file are used.

The following are the full commands to use for Windows, Linux, and macOS. The only difference is that on Windows systems you use semicolons to separate class path items, while you use colons for that purpose on Linux and macOS.

Here is the full command for Windows:
```
java -classpath SampleAcn.jar;SampleLM.jar
 -Djava.security.manager
 -Djava.security.policy==sampleacn.policy
 -Djava.security.auth.login.config==sample_jaas.config
 sample.SampleAcn
```
Here is the full command for Linux and macOS:
```
java -classpath SampleAcn.jar:SampleLM.jar
 -Djava.security.manager
 -Djava.security.policy==sampleacn.policy
 -Djava.security.auth.login.config==sample_jaas.config
 sample.SampleAcn
```
Type all that on one line. Multiple lines are used here for legibility. If the command is too long for your system, you may need to place it in a .bat file (for Windows) or a .sh file (for Linux and macOS) and then run that file to execute the command.

Since the specified policy file contains an entry granting the code the required permissions, execution should proceed without any exceptions indicating a required permission was not granted. You will be prompted for a user name and password (use testUser and testPassword), and the SampleLoginModule specified in the login configuration file will check the name and password. If your login is successful, you will see the message Authentication succeeded! and if not, you will see Authentication failed: followed by a reason for the failure.

sampleacn.policy

/* grant the sample LoginModule permissions */
grant codebase "file:./SampleLM.jar" {
    permission javax.security.auth.AuthPermission "modifyPrincipals";
};

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