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package com.sun.security.auth.module;

import java.io.*;
import java.text.MessageFormat;
import java.util.*;

import javax.security.auth.*;
import javax.security.auth.kerberos.KerberosTicket;
import javax.security.auth.kerberos.KerberosPrincipal;
import javax.security.auth.kerberos.KerberosKey;
import javax.security.auth.kerberos.KeyTab;
import javax.security.auth.callback.*;
import javax.security.auth.login.*;
import javax.security.auth.spi.*;

import sun.security.krb5.*;
import sun.security.jgss.krb5.Krb5Util;
import sun.security.krb5.Credentials;
import sun.security.util.HexDumpEncoder;
import static sun.security.util.ResourcesMgr.getAuthResourceString;


This LoginModule authenticates users using Kerberos protocols. 
 The configuration entry for Krb5LoginModule has several options that control the authentication process and additions to the Subject's private credential set. Irrespective of these options, the Subject's principal set and private credentials set are updated only when commit is called. When commit is called, the KerberosPrincipal is added to the Subject's principal set (unless the principal is specified as "*"). If isInitiator is true, the KerberosTicket is added to the Subject's private credentials. 
 If the configuration entry for KerberosLoginModule has the option storeKey set to true, then KerberosKey or KeyTab will also be added to the subject's private credentials. KerberosKey, the principal's key(s) will be derived from user's password, and KeyTab is the keytab used when useKeyTab is set to true. The KeyTab object is restricted to be used by the specified principal unless the principal value is "*". 
 This LoginModule recognizes the doNotPrompt option. If set to true the user will not be prompted for the password. 
 The user can specify the location of the ticket cache by using the option ticketCache in the configuration entry. 
The user can specify the keytab location by using the option keyTab in the configuration entry. 
 The principal name can be specified in the configuration entry by using the option principal. The principal name can either be a simple user name, a service name such as host/mission.eng.sun.com, or "*". The principal can also be set using the system property sun.security.krb5.principal. This property is checked during login. If this property is not set, then the principal name from the configuration is used. In the case where the principal property is not set and the principal entry also does not exist, the user is prompted for the name. When this property of entry is set, and useTicketCache is set to true, only TGT belonging to this principal is used. 
 The following is a list of configuration options supported for Krb5LoginModule: 


refreshKrb5Config:


 Set this to true, if you want the configuration to be refreshed before the login method is called.


useTicketCache:


Set this to true, if you want the TGT to be obtained from the ticket cache. Set this option to false if you do not want this module to use the ticket cache. (Default is False). This module will search for the ticket cache in the following locations: On Solaris and Linux it will look for the ticket cache in /tmp/krb5cc_uid where the uid is numeric user identifier. If the ticket cache is not available in the above location, or if we are on a Windows platform, it will look for the cache as {user.home}{file.separator}krb5cc_{user.name}. You can override the ticket cache location by using ticketCache. For Windows, if a ticket cannot be retrieved from the file ticket cache, it will use Local Security Authority (LSA) API to get the TGT. 
ticketCache:


Set this to the name of the ticket cache that contains user's TGT. If this is set, useTicketCache must also be set to true; Otherwise a configuration error will be returned.


renewTGT:


Set this to true, if you want to renew the TGT when it's more than half-way expired (the time until expiration is less than the time since start time). If this is set, useTicketCache must also be set to true; otherwise a configuration error will be returned.


doNotPrompt:


Set this to true if you do not want to be
prompted for the password
if credentials can not be obtained from the cache, the keytab,
or through shared state.(Default is false)
If set to true, credential must be obtained through cache, keytab,
or shared state. Otherwise, authentication will fail.


useKeyTab:


Set this to true if you want the module to get the principal's key from the the keytab.(default value is False) If keytab is not set then the module will locate the keytab from the Kerberos configuration file. If it is not specified in the Kerberos configuration file then it will look for the file {user.home}{file.separator}krb5.keytab.


keyTab:


Set this to the file name of the
keytab to get principal's secret key.


storeKey:


Set this to true to if you want the keytab or the principal's key to be stored in the Subject's private credentials. For isInitiator being false, if principal is "*", the KeyTab stored can be used by anyone, otherwise, it's restricted to be used by the specified principal only.


principal:


The name of the principal that should be used. The principal can be a simple username such as "testuser" or a service name such as "host/testhost.eng.sun.com". You can use the principal option to set the principal when there are credentials for multiple principals in the keyTab or when you want a specific ticket cache only. The principal can also be set using the system property sun.security.krb5.principal. In addition, if this system property is defined, then it will be used. If this property is not set, then the principal name from the configuration will be used. The principal name can be set to "*" when isInitiator is false. In this case, the acceptor is not bound to a single principal. It can act as any principal an initiator requests if keys for that principal can be found. When isInitiator is true, the principal name cannot be set to "*". 


isInitiator:


Set this to true, if initiator. Set this to false, if acceptor only.
(Default is true).
Note: Do not set this value to false for initiators.




 This LoginModule also recognizes the following additional Configuration options that enable you to share username and passwords across different authentication modules: 

   
useFirstPass:

                  
if, true, this LoginModule retrieves the
                  username and password from the module's shared state,
                  using "javax.security.auth.login.name" and
                  "javax.security.auth.login.password" as the respective
                  keys. The retrieved values are used for authentication.
                  If authentication fails, no attempt for a retry
                  is made, and the failure is reported back to the
                  calling application.

   
tryFirstPass:

                  
if, true, this LoginModule retrieves the
                  the username and password from the module's shared
                  state using "javax.security.auth.login.name" and
                  "javax.security.auth.login.password" as the respective
                  keys.  The retrieved values are used for
                  authentication.
                  If authentication fails, the module uses the
                  CallbackHandler to retrieve a new username
                  and password, and another attempt to authenticate
                  is made. If the authentication fails,
                  the failure is reported back to the calling application

   
storePass:

                  
if, true, this LoginModule stores the username and
                  password obtained from the CallbackHandler in the
                  modules shared state, using
                  "javax.security.auth.login.name" and
                  "javax.security.auth.login.password" as the respective
                  keys.  This is not performed if existing values already
                  exist for the username and password in the shared
                  state, or if authentication fails.

   
clearPass:

                  
if, true, this LoginModule clears the
                  username and password stored in the module's shared
                  state  after both phases of authentication
                  (login and commit) have completed.




If the principal system property or key is already provided, the value of
"javax.security.auth.login.name" in the shared state is ignored.

When multiple mechanisms to retrieve a ticket or key is provided, the
preference order is:

    

  1. ticket cache

  2. keytab

  3. shared state

  4. user prompt



Note that if any step fails, it will fallback to the next step. There's only one exception, if the shared state step fails and useFirstPass = true, no user prompt is made. 
Examples of some configuration values for Krb5LoginModule in
JAAS config file and the results are:




doNotPrompt = true
 This is an illegal combination since none of useTicketCache,
useKeyTab, useFirstPass and tryFirstPass is set and the user can not be prompted for the password. 

ticketCache = <filename>
 This is an illegal combination since useTicketCache is not set to true and the ticketCache is set. A configuration error will occur. 

renewTGT = true
 This is an illegal combination since useTicketCache is not set to true and renewTGT is set. A configuration error will occur. 

storeKey = true  useTicketCache = true  doNotPrompt = true
 This is an illegal combination since storeKey is set to true but the key can not be obtained either by prompting the user or from the keytab, or from the shared state. A configuration error will occur. 

keyTab = <filename>  doNotPrompt = true

This is an illegal combination since useKeyTab is not set to true and
the keyTab is set. A configuration error will occur.


debug = true
 Prompt the user for the principal name and the password. Use the authentication exchange to get TGT from the KDC and populate the Subject with the principal and TGT. Output debug messages. 

useTicketCache = true  doNotPrompt = true
 Check the default cache for TGT and populate the Subject with the principal and TGT. If the TGT is not available, do not prompt the user, instead fail the authentication. 

principal = <name>  useTicketCache = true  doNotPrompt = true

Get the TGT from the default cache for the principal and populate the
Subject's principal and private creds set. If ticket cache is
not available or does not contain the principal's TGT
authentication will fail.


useTicketCache = true
ticketCache = <file name>
useKeyTab = true
keyTab = <keytab filename>
principal = <principal name>
doNotPrompt = true

Search the cache for the principal's TGT. If it is not available
use the key in the keytab to perform authentication exchange with the
KDC and acquire the TGT.
The Subject will be populated with the principal and the TGT.
If the key is not available or valid then authentication will fail.


useTicketCache = true  ticketCache = <filename>

The TGT will be obtained from the cache specified.
The Kerberos principal name used will be the principal name in
the Ticket cache. If the TGT is not available in the
ticket cache the user will be prompted for the principal name
and the password. The TGT will be obtained using the authentication
exchange with the KDC.
The Subject will be populated with the TGT.


useKeyTab = true  keyTab=<keytab filename>  principal = <principal name>  storeKey = true

The key for the principal will be retrieved from the keytab.
If the key is not available in the keytab the user will be prompted
for the principal's password. The Subject will be populated
with the principal's key either from the keytab or derived from the
password entered.


useKeyTab = true  keyTab = <keytabname>  storeKey = true  doNotPrompt = false

The user will be prompted for the service principal name.
If the principal's
longterm key is available in the keytab , it will be added to the
Subject's private credentials. An authentication exchange will be
attempted with the principal name and the key from the Keytab.
If successful the TGT will be added to the
Subject's private credentials set. Otherwise the authentication will fail.


isInitiator = false  useKeyTab = true  keyTab = <keytabname>  storeKey = true  principal = *

The acceptor will be an unbound acceptor and it can act as any principal
as long that principal has keys in the keytab.


useTicketCache = true
ticketCache = <file name>
useKeyTab = true
keyTab = <file name>
storeKey = true
principal = <principal name>
 The client's TGT will be retrieved from the ticket cache and added to the Subject's private credentials. If the TGT is not available in the ticket cache, or the TGT's client name does not match the principal name, Java will use a secret key to obtain the TGT using the authentication exchange and added to the Subject's private credentials. This secret key will be first retrieved from the keytab. If the key is not available, the user will be prompted for the password. In either case, the key derived from the password will be added to the Subject's private credentials set. 

isInitiator = false

Configured to act as acceptor only, credentials are not acquired
via AS exchange. For acceptors only, set this value to false.
For initiators, do not set this value to false.


isInitiator = true

Configured to act as initiator, credentials are acquired
via AS exchange. For initiators, set this value to true, or leave this
option unset, in which case default value (true) will be used.



Author:Ram Marti
/**
 * This {@code LoginModule} authenticates users using
 * Kerberos protocols.
 *
 * <p> The configuration entry for {@code Krb5LoginModule} has
 * several options that control the authentication process and
 * additions to the {@code Subject}'s private credential
 * set. Irrespective of these options, the {@code Subject}'s
 * principal set and private credentials set are updated only when
 * {@code commit} is called.
 * When {@code commit} is called, the {@code KerberosPrincipal}
 * is added to the {@code Subject}'s principal set (unless the
 * {@code principal} is specified as "*"). If {@code isInitiator}
 * is true, the {@code KerberosTicket} is
 * added to the {@code Subject}'s private credentials.
 *
 * <p> If the configuration entry for {@code KerberosLoginModule}
 * has the option {@code storeKey} set to true, then
 * {@code KerberosKey} or {@code KeyTab} will also be added to the
 * subject's private credentials. {@code KerberosKey}, the principal's
 * key(s) will be derived from user's password, and {@code KeyTab} is
 * the keytab used when {@code useKeyTab} is set to true. The
 * {@code KeyTab} object is restricted to be used by the specified
 * principal unless the principal value is "*".
 *
 * <p> This {@code LoginModule} recognizes the {@code doNotPrompt}
 * option. If set to true the user will not be prompted for the password.
 *
 * <p> The user can  specify the location of the ticket cache by using
 * the option {@code ticketCache} in the configuration entry.
 *
 * <p>The user can specify the keytab location by using
 * the option {@code keyTab}
 * in the configuration entry.
 *
 * <p> The principal name can be specified in the configuration entry
 * by using the option {@code principal}. The principal name
 * can either be a simple user name, a service name such as
 * {@code host/mission.eng.sun.com}, or "*". The principal can also
 * be set using the system property {@code sun.security.krb5.principal}.
 * This property is checked during login. If this property is not set, then
 * the principal name from the configuration is used. In the
 * case where the principal property is not set and the principal
 * entry also does not exist, the user is prompted for the name.
 * When this property of entry is set, and {@code useTicketCache}
 * is set to true, only TGT belonging to this principal is used.
 *
 * <p> The following is a list of configuration options supported
 * for {@code Krb5LoginModule}:
 * <blockquote><dl>
 * <dt>{@code refreshKrb5Config}:</dt>
 * <dd> Set this to true, if you want the configuration
 * to be refreshed before the {@code login} method is called.</dd>
 * <dt>{@code useTicketCache}:</dt>
 * <dd>Set this to true, if you want the
 * TGT to be obtained from the ticket cache. Set this option
 * to false if you do not want this module to use the ticket cache.
 * (Default is False).
 * This module will search for the ticket
 * cache in the following locations: On Solaris and Linux
 * it will look for the ticket cache in /tmp/krb5cc_{@code uid}
 * where the uid is numeric user identifier. If the ticket cache is
 * not available in the above location, or if we are on a
 * Windows platform, it will look for the cache as
 * {user.home}{file.separator}krb5cc_{user.name}.
 * You can override the ticket cache location by using
 * {@code ticketCache}.
 * For Windows, if a ticket cannot be retrieved from the file ticket cache,
 * it will use Local Security Authority (LSA) API to get the TGT.
 * <dt>{@code ticketCache}:</dt>
 * <dd>Set this to the name of the ticket
 * cache that  contains user's TGT.
 * If this is set,  {@code useTicketCache}
 * must also be set to true; Otherwise a configuration error will
 * be returned.</dd>
 * <dt>{@code renewTGT}:</dt>
 * <dd>Set this to true, if you want to renew the TGT when it's more than
 * half-way expired (the time until expiration is less than the time
 * since start time). If this is set, {@code useTicketCache} must also be
 * set to true; otherwise a configuration error will be returned.</dd>
 * <dt>{@code doNotPrompt}:</dt>
 * <dd>Set this to true if you do not want to be
 * prompted for the password
 * if credentials can not be obtained from the cache, the keytab,
 * or through shared state.(Default is false)
 * If set to true, credential must be obtained through cache, keytab,
 * or shared state. Otherwise, authentication will fail.</dd>
 * <dt>{@code useKeyTab}:</dt>
 * <dd>Set this to true if you
 * want the module to get the principal's key from the
 * the keytab.(default value is False)
 * If {@code keytab} is not set then
 * the module will locate the keytab from the
 * Kerberos configuration file.
 * If it is not specified in the Kerberos configuration file
 * then it will look for the file
 * {@code {user.home}{file.separator}}krb5.keytab.</dd>
 * <dt>{@code keyTab}:</dt>
 * <dd>Set this to the file name of the
 * keytab to get principal's secret key.</dd>
 * <dt>{@code storeKey}:</dt>
 * <dd>Set this to true to if you want the keytab or the
 * principal's key to be stored in the Subject's private credentials.
 * For {@code isInitiator} being false, if {@code principal}
 * is "*", the {@link KeyTab} stored can be used by anyone, otherwise,
 * it's restricted to be used by the specified principal only.</dd>
 * <dt>{@code principal}:</dt>
 * <dd>The name of the principal that should
 * be used. The principal can be a simple username such as
 * "{@code testuser}" or a service name such as
 * "{@code host/testhost.eng.sun.com}". You can use the
 * {@code principal}  option to set the principal when there are
 * credentials for multiple principals in the
 * {@code keyTab} or when you want a specific ticket cache only.
 * The principal can also be set using the system property
 * {@code sun.security.krb5.principal}. In addition, if this
 * system property is defined, then it will be used. If this property
 * is not set, then the principal name from the configuration will be
 * used.
 * The principal name can be set to "*" when {@code isInitiator} is false.
 * In this case, the acceptor is not bound to a single principal. It can
 * act as any principal an initiator requests if keys for that principal
 * can be found. When {@code isInitiator} is true, the principal name
 * cannot be set to "*".
 * </dd>
 * <dt>{@code isInitiator}:</dt>
 * <dd>Set this to true, if initiator. Set this to false, if acceptor only.
 * (Default is true).
 * Note: Do not set this value to false for initiators.</dd>
 * </dl></blockquote>
 *
 * <p> This {@code LoginModule} also recognizes the following additional
 * {@code Configuration}
 * options that enable you to share username and passwords across different
 * authentication modules:
 * <blockquote><dl>
 *
 *    <dt>{@code useFirstPass}:</dt>
 *                   <dd>if, true, this LoginModule retrieves the
 *                   username and password from the module's shared state,
 *                   using "javax.security.auth.login.name" and
 *                   "javax.security.auth.login.password" as the respective
 *                   keys. The retrieved values are used for authentication.
 *                   If authentication fails, no attempt for a retry
 *                   is made, and the failure is reported back to the
 *                   calling application.</dd>
 *
 *    <dt>{@code tryFirstPass}:</dt>
 *                   <dd>if, true, this LoginModule retrieves the
 *                   the username and password from the module's shared
 *                   state using "javax.security.auth.login.name" and
 *                   "javax.security.auth.login.password" as the respective
 *                   keys.  The retrieved values are used for
 *                   authentication.
 *                   If authentication fails, the module uses the
 *                   CallbackHandler to retrieve a new username
 *                   and password, and another attempt to authenticate
 *                   is made. If the authentication fails,
 *                   the failure is reported back to the calling application</dd>
 *
 *    <dt>{@code storePass}:</dt>
 *                   <dd>if, true, this LoginModule stores the username and
 *                   password obtained from the CallbackHandler in the
 *                   modules shared state, using
 *                   "javax.security.auth.login.name" and
 *                   "javax.security.auth.login.password" as the respective
 *                   keys.  This is not performed if existing values already
 *                   exist for the username and password in the shared
 *                   state, or if authentication fails.</dd>
 *
 *    <dt>{@code clearPass}:</dt>
 *                   <dd>if, true, this LoginModule clears the
 *                   username and password stored in the module's shared
 *                   state  after both phases of authentication
 *                   (login and commit) have completed.</dd>
 * </dl></blockquote>
 * <p>If the principal system property or key is already provided, the value of
 * "javax.security.auth.login.name" in the shared state is ignored.
 * <p>When multiple mechanisms to retrieve a ticket or key is provided, the
 * preference order is:
 * <ol>
 * <li>ticket cache
 * <li>keytab
 * <li>shared state
 * <li>user prompt
 * </ol>
 *
 * <p>Note that if any step fails, it will fallback to the next step.
 * There's only one exception, if the shared state step fails and
 * {@code useFirstPass = true}, no user prompt is made.
 * <p>Examples of some configuration values for Krb5LoginModule in
 * JAAS config file and the results are:
 * <blockquote>
 * <pre>{@code
 * doNotPrompt = true}</pre>
 * This is an illegal combination since none of {@code useTicketCache,
 * useKeyTab, useFirstPass} and {@code tryFirstPass}
 * is set and the user can not be prompted for the password.
 *
 * <pre>{@code
 * ticketCache = <filename>}</pre>
 * This is an illegal combination since {@code useTicketCache}
 * is not set to true and the ticketCache is set. A configuration error
 * will occur.
 *
 * <pre>{@code
 * renewTGT = true}</pre>
 * This is an illegal combination since {@code useTicketCache} is
 * not set to true and renewTGT is set. A configuration error will occur.
 *
 * <pre>{@code
 * storeKey = true  useTicketCache = true  doNotPrompt = true}</pre>
 * This is an illegal combination since  {@code storeKey} is set to
 * true but the key can not be obtained either by prompting the user or from
 * the keytab, or from the shared state. A configuration error will occur.
 *
 * <pre>{@code
 * keyTab = <filename>  doNotPrompt = true}</pre>
 * This is an illegal combination since useKeyTab is not set to true and
 * the keyTab is set. A configuration error will occur.
 *
 * <pre>{@code
 * debug = true}</pre>
 * Prompt the user for the principal name and the password.
 * Use the authentication exchange to get TGT from the KDC and
 * populate the {@code Subject} with the principal and TGT.
 * Output debug messages.
 *
 * <pre>{@code
 * useTicketCache = true  doNotPrompt = true}</pre>
 * Check the default cache for TGT and populate the {@code Subject}
 * with the principal and TGT. If the TGT is not available,
 * do not prompt the user, instead fail the authentication.
 *
 * <pre>{@code
 * principal = <name>  useTicketCache = true  doNotPrompt = true}</pre>
 * Get the TGT from the default cache for the principal and populate the
 * Subject's principal and private creds set. If ticket cache is
 * not available or does not contain the principal's TGT
 * authentication will fail.
 *
 * <pre>{@code
 * useTicketCache = true
 * ticketCache = <file name>
 * useKeyTab = true
 * keyTab = <keytab filename>
 * principal = <principal name>
 * doNotPrompt = true}</pre>
 * Search the cache for the principal's TGT. If it is not available
 * use the key in the keytab to perform authentication exchange with the
 * KDC and acquire the TGT.
 * The Subject will be populated with the principal and the TGT.
 * If the key is not available or valid then authentication will fail.
 *
 * <pre>{@code
 * useTicketCache = true  ticketCache = <filename>}</pre>
 * The TGT will be obtained from the cache specified.
 * The Kerberos principal name used will be the principal name in
 * the Ticket cache. If the TGT is not available in the
 * ticket cache the user will be prompted for the principal name
 * and the password. The TGT will be obtained using the authentication
 * exchange with the KDC.
 * The Subject will be populated with the TGT.
 *
 * <pre>{@code
 * useKeyTab = true  keyTab=<keytab filename>  principal = <principal name>  storeKey = true}</pre>
 * The key for the principal will be retrieved from the keytab.
 * If the key is not available in the keytab the user will be prompted
 * for the principal's password. The Subject will be populated
 * with the principal's key either from the keytab or derived from the
 * password entered.
 *
 * <pre>{@code
 * useKeyTab = true  keyTab = <keytabname>  storeKey = true  doNotPrompt = false}</pre>
 * The user will be prompted for the service principal name.
 * If the principal's
 * longterm key is available in the keytab , it will be added to the
 * Subject's private credentials. An authentication exchange will be
 * attempted with the principal name and the key from the Keytab.
 * If successful the TGT will be added to the
 * Subject's private credentials set. Otherwise the authentication will fail.
 *
 * <pre>{@code
 * isInitiator = false  useKeyTab = true  keyTab = <keytabname>  storeKey = true  principal = *}</pre>
 * The acceptor will be an unbound acceptor and it can act as any principal
 * as long that principal has keys in the keytab.
 *
 * <pre>{@code
 * useTicketCache = true
 * ticketCache = <file name>
 * useKeyTab = true
 * keyTab = <file name>
 * storeKey = true
 * principal = <principal name>}</pre>
 * The client's TGT will be retrieved from the ticket cache and added to the
 * {@code Subject}'s private credentials. If the TGT is not available
 * in the ticket cache, or the TGT's client name does not match the principal
 * name, Java will use a secret key to obtain the TGT using the authentication
 * exchange and added to the Subject's private credentials.
 * This secret key will be first retrieved from the keytab. If the key
 * is not available, the user will be prompted for the password. In either
 * case, the key derived from the password will be added to the
 * Subject's private credentials set.
 *
 * <pre>{@code
 * isInitiator = false}</pre>
 * Configured to act as acceptor only, credentials are not acquired
 * via AS exchange. For acceptors only, set this value to false.
 * For initiators, do not set this value to false.
 *
 * <pre>{@code
 * isInitiator = true}</pre>
 * Configured to act as initiator, credentials are acquired
 * via AS exchange. For initiators, set this value to true, or leave this
 * option unset, in which case default value (true) will be used.
 *
 * </blockquote>
 *
 * @author Ram Marti
 */

public class Krb5LoginModule implements LoginModule {

    // initial state
    private Subject subject;
    private CallbackHandler callbackHandler;
    private Map<String, Object> sharedState;
    private Map<String, ?> options;

    // configurable option
    private boolean debug = false;
    private boolean storeKey = false;
    private boolean doNotPrompt = false;
    private boolean useTicketCache = false;
    private boolean useKeyTab = false;
    private String ticketCacheName = null;
    private String keyTabName = null;
    private String princName = null;

    private boolean useFirstPass = false;
    private boolean tryFirstPass = false;
    private boolean storePass = false;
    private boolean clearPass = false;
    private boolean refreshKrb5Config = false;
    private boolean renewTGT = false;

    // specify if initiator.
    // perform authentication exchange if initiator
    private boolean isInitiator = true;

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

    // Encryption keys calculated from password. Assigned when storekey == true
    // and useKeyTab == false (or true but not found)
    private EncryptionKey[] encKeys = null;

    KeyTab ktab = null;

    private Credentials cred = null;

    private PrincipalName principal = null;
    private KerberosPrincipal kerbClientPrinc = null;
    private KerberosTicket kerbTicket = null;
    private KerberosKey[] kerbKeys = null;
    private StringBuffer krb5PrincName = null;
    private boolean unboundServer = false;
    private char[] password = null;

    private static final String NAME = "javax.security.auth.login.name";
    private static final String PWD = "javax.security.auth.login.password";

    
Initialize this LoginModule. 
Params:
  • subject – the Subject to be authenticated.
  • callbackHandler – a CallbackHandler for communication with the end user (prompting for usernames and passwords, for example).
  • sharedState – shared LoginModule state.
  • options – options specified in the login Configuration for this particular LoginModule.
/**
     * Initialize this {@code LoginModule}.
     *
     * @param subject the {@code Subject} to be authenticated.
     *
     * @param callbackHandler a {@code CallbackHandler} for
     *                  communication with the end user (prompting for
     *                  usernames and passwords, for example).
     *
     * @param sharedState shared {@code LoginModule} state.
     *
     * @param options options specified in the login
     *                  {@code Configuration} for this particular
     *                  {@code LoginModule}.
     */
    // Unchecked warning from (Map<String, Object>)sharedState is safe
    // since javax.security.auth.login.LoginContext passes a raw HashMap.
    // Unchecked warnings from options.get(String) are safe since we are
    // passing known keys.
    @SuppressWarnings("unchecked")
    public void initialize(Subject subject,
                           CallbackHandler callbackHandler,
                           Map<String, ?> sharedState,
                           Map<String, ?> options) {

        this.subject = subject;
        this.callbackHandler = callbackHandler;
        this.sharedState = (Map<String, Object>)sharedState;
        this.options = options;

        // initialize any configured options

        debug = "true".equalsIgnoreCase((String)options.get("debug"));
        storeKey = "true".equalsIgnoreCase((String)options.get("storeKey"));
        doNotPrompt = "true".equalsIgnoreCase((String)options.get
                                              ("doNotPrompt"));
        useTicketCache = "true".equalsIgnoreCase((String)options.get
                                                 ("useTicketCache"));
        useKeyTab = "true".equalsIgnoreCase((String)options.get("useKeyTab"));
        ticketCacheName = (String)options.get("ticketCache");
        keyTabName = (String)options.get("keyTab");
        if (keyTabName != null) {
            keyTabName = sun.security.krb5.internal.ktab.KeyTab.normalize(
                         keyTabName);
        }
        princName = (String)options.get("principal");
        refreshKrb5Config =
            "true".equalsIgnoreCase((String)options.get("refreshKrb5Config"));
        renewTGT =
            "true".equalsIgnoreCase((String)options.get("renewTGT"));

        // check isInitiator value
        String isInitiatorValue = ((String)options.get("isInitiator"));
        if (isInitiatorValue == null) {
            // use default, if value not set
        } else {
            isInitiator = "true".equalsIgnoreCase(isInitiatorValue);
        }

        tryFirstPass =
            "true".equalsIgnoreCase
            ((String)options.get("tryFirstPass"));
        useFirstPass =
            "true".equalsIgnoreCase
            ((String)options.get("useFirstPass"));
        storePass =
            "true".equalsIgnoreCase((String)options.get("storePass"));
        clearPass =
            "true".equalsIgnoreCase((String)options.get("clearPass"));
        if (debug) {
            System.out.print("Debug is  " + debug
                             + " storeKey " + storeKey
                             + " useTicketCache " + useTicketCache
                             + " useKeyTab " + useKeyTab
                             + " doNotPrompt " + doNotPrompt
                             + " ticketCache is " + ticketCacheName
                             + " isInitiator " + isInitiator
                             + " KeyTab is " + keyTabName
                             + " refreshKrb5Config is " + refreshKrb5Config
                             + " principal is " + princName
                             + " tryFirstPass is " + tryFirstPass
                             + " useFirstPass is " + useFirstPass
                             + " storePass is " + storePass
                             + " clearPass is " + clearPass + "\n");
        }
    }


    
Authenticate the user

Throws:
Returns:true in all cases since this LoginModule should not be ignored.
/**
     * Authenticate the user
     *
     * @return true in all cases since this {@code LoginModule}
     *          should not be ignored.
     *
     * @exception FailedLoginException if the authentication fails.
     *
     * @exception LoginException if this {@code LoginModule}
     *          is unable to perform the authentication.
     */
    public boolean login() throws LoginException {

        if (refreshKrb5Config) {
            try {
                if (debug) {
                    System.out.println("Refreshing Kerberos configuration");
                }
                sun.security.krb5.Config.refresh();
            } catch (KrbException ke) {
                LoginException le = new LoginException(ke.getMessage());
                le.initCause(ke);
                throw le;
            }
        }
        String principalProperty = System.getProperty
            ("sun.security.krb5.principal");
        if (principalProperty != null) {
            krb5PrincName = new StringBuffer(principalProperty);
        } else {
            if (princName != null) {
                krb5PrincName = new StringBuffer(princName);
            }
        }

        validateConfiguration();

        if (krb5PrincName != null && krb5PrincName.toString().equals("*")) {
            unboundServer = true;
        }

        if (tryFirstPass) {
            try {
                attemptAuthentication(true);
                if (debug)
                    System.out.println("\t\t[Krb5LoginModule] " +
                                       "authentication succeeded");
                succeeded = true;
                cleanState();
                return true;
            } catch (LoginException le) {
                // authentication failed -- try again below by prompting
                cleanState();
                if (debug) {
                    System.out.println("\t\t[Krb5LoginModule] " +
                                       "tryFirstPass failed with:" +
                                       le.getMessage());
                }
            }
        } else if (useFirstPass) {
            try {
                attemptAuthentication(true);
                succeeded = true;
                cleanState();
                return true;
            } catch (LoginException e) {
                // authentication failed -- clean out state
                if (debug) {
                    System.out.println("\t\t[Krb5LoginModule] " +
                                       "authentication failed \n" +
                                       e.getMessage());
                }
                succeeded = false;
                cleanState();
                throw e;
            }
        }

        // attempt the authentication by getting the username and pwd
        // by prompting or configuration i.e. not from shared state

        try {
            attemptAuthentication(false);
            succeeded = true;
            cleanState();
            return true;
        } catch (LoginException e) {
            // authentication failed -- clean out state
            if (debug) {
                System.out.println("\t\t[Krb5LoginModule] " +
                                   "authentication failed \n" +
                                   e.getMessage());
            }
            succeeded = false;
            cleanState();
            throw e;
        }
    }
    
process the configuration options
Get the TGT either out of
cache or from the KDC using the password entered
Check the  permission before getting the TGT

/**
     * process the configuration options
     * Get the TGT either out of
     * cache or from the KDC using the password entered
     * Check the  permission before getting the TGT
     */

    private void attemptAuthentication(boolean getPasswdFromSharedState)
        throws LoginException {

        /*
         * Check the creds cache to see whether
         * we have TGT for this client principal
         */
        if (krb5PrincName != null) {
            try {
                principal = new PrincipalName
                    (krb5PrincName.toString(),
                     PrincipalName.KRB_NT_PRINCIPAL);
            } catch (KrbException e) {
                LoginException le = new LoginException(e.getMessage());
                le.initCause(e);
                throw le;
            }
        }

        try {
            if (useTicketCache) {
                // ticketCacheName == null implies the default cache
                if (debug)
                    System.out.println("Acquire TGT from Cache");
                cred  = Credentials.acquireTGTFromCache
                    (principal, ticketCacheName);

                if (cred != null) {
                    if (renewTGT && isOld(cred)) {
                        // renew if ticket is old.
                        Credentials newCred = renewCredentials(cred);
                        if (newCred != null) {
                            newCred.setProxy(cred.getProxy());
                            cred = newCred;
                        }
                    }
                    if (!isCurrent(cred)) {
                        // credentials have expired
                        cred = null;
                        if (debug)
                            System.out.println("Credentials are" +
                                    " no longer valid");
                    }
                }

                if (cred != null) {
                   // get the principal name from the ticket cache
                   if (principal == null) {
                        principal = cred.getClient();
                   }
                }
                if (debug) {
                    System.out.println("Principal is " + principal);
                    if (cred == null) {
                        System.out.println
                            ("null credentials from Ticket Cache");
                    }
                }
            }

            // cred = null indicates that we didn't get the creds
            // from the cache or useTicketCache was false

            if (cred == null) {
                // We need the principal name whether we use keytab
                // or AS Exchange
                if (principal == null) {
                    promptForName(getPasswdFromSharedState);
                    principal = new PrincipalName
                        (krb5PrincName.toString(),
                         PrincipalName.KRB_NT_PRINCIPAL);
                }

                /*
                 * Before dynamic KeyTab support (6894072), here we check if
                 * the keytab contains keys for the principal. If no, keytab
                 * will not be used and password is prompted for.
                 *
                 * After 6894072, we normally don't check it, and expect the
                 * keys can be populated until a real connection is made. The
                 * check is still done when isInitiator == true, where the keys
                 * will be used right now.
                 *
                 * Probably tricky relations:
                 *
                 * useKeyTab is config flag, but when it's true but the ktab
                 * does not contains keys for principal, we would use password
                 * and keep the flag unchanged (for reuse?). In this method,
                 * we use (ktab != null) to check whether keytab is used.
                 * After this method (and when storeKey == true), we use
                 * (encKeys == null) to check.
                 */
                if (useKeyTab) {
                    if (!unboundServer) {
                        KerberosPrincipal kp =
                                new KerberosPrincipal(principal.getName());
                        ktab = (keyTabName == null)
                                ? KeyTab.getInstance(kp)
                                : KeyTab.getInstance(kp, new File(keyTabName));
                    } else {
                        ktab = (keyTabName == null)
                                ? KeyTab.getUnboundInstance()
                                : KeyTab.getUnboundInstance(new File(keyTabName));
                    }
                    if (isInitiator) {
                        if (Krb5Util.keysFromJavaxKeyTab(ktab, principal).length
                                == 0) {
                            ktab = null;
                            if (debug) {
                                System.out.println
                                    ("Key for the principal " +
                                     principal  +
                                     " not available in " +
                                     ((keyTabName == null) ?
                                      "default key tab" : keyTabName));
                            }
                        }
                    }
                }

                KrbAsReqBuilder builder;

                if (ktab == null) {
                    promptForPass(getPasswdFromSharedState);
                    builder = new KrbAsReqBuilder(principal, password);
                    if (isInitiator) {
                        // XXX Even if isInitiator=false, it might be
                        // better to do an AS-REQ so that keys can be
                        // updated with PA info
                        cred = builder.action().getCreds();
                    }
                    if (storeKey) {
                        encKeys = builder.getKeys(isInitiator);
                        // When encKeys is empty, the login actually fails.
                        // For compatibility, exception is thrown in commit().
                    }
                } else {
                    builder = new KrbAsReqBuilder(principal, ktab);
                    if (isInitiator) {
                        cred = builder.action().getCreds();
                    }
                }
                builder.destroy();

                if (debug) {
                    System.out.println("principal is " + principal);
                    HexDumpEncoder hd = new HexDumpEncoder();
                    if (ktab != null) {
                        System.out.println("Will use keytab");
                    } else if (storeKey) {
                        for (int i = 0; i < encKeys.length; i++) {
                            System.out.println("EncryptionKey: keyType=" +
                                encKeys[i].getEType() +
                                " keyBytes (hex dump)=" +
                                hd.encodeBuffer(encKeys[i].getBytes()));
                        }
                    }
                }

                // we should hava a non-null cred
                if (isInitiator && (cred == null)) {
                    throw new LoginException
                        ("TGT Can not be obtained from the KDC ");
                }

            }
        } catch (KrbException e) {
            LoginException le = new LoginException(e.getMessage());
            le.initCause(e);
            throw le;
        } catch (IOException ioe) {
            LoginException ie = new LoginException(ioe.getMessage());
            ie.initCause(ioe);
            throw ie;
        }
    }

    private void promptForName(boolean getPasswdFromSharedState)
        throws LoginException {
        krb5PrincName = new StringBuffer("");
        if (getPasswdFromSharedState) {
            // use the name saved by the first module in the stack
            username = (String)sharedState.get(NAME);
            if (debug) {
                System.out.println
                    ("username from shared state is " + username + "\n");
            }
            if (username == null) {
                System.out.println
                    ("username from shared state is null\n");
                throw new LoginException
                    ("Username can not be obtained from sharedstate ");
            }
            if (debug) {
                System.out.println
                    ("username from shared state is " + username + "\n");
            }
            if (username != null && username.length() > 0) {
                krb5PrincName.insert(0, username);
                return;
            }
        }

        if (doNotPrompt) {
            throw new LoginException
                ("Unable to obtain Principal Name for authentication ");
        } else {
            if (callbackHandler == null)
                throw new LoginException("No CallbackHandler "
                                         + "available "
                                         + "to garner authentication "
                                         + "information from the user");
            try {
                String defUsername = System.getProperty("user.name");

                Callback[] callbacks = new Callback[1];
                MessageFormat form = new MessageFormat(
                                       getAuthResourceString(
                                       "Kerberos.username.defUsername."));
                Object[] source =  {defUsername};
                callbacks[0] = new NameCallback(form.format(source));
                callbackHandler.handle(callbacks);
                username = ((NameCallback)callbacks[0]).getName();
                if (username == null || username.length() == 0)
                    username = defUsername;
                krb5PrincName.insert(0, username);

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

    private void promptForPass(boolean getPasswdFromSharedState)
        throws LoginException {

        if (getPasswdFromSharedState) {
            // use the password saved by the first module in the stack
            password = (char[])sharedState.get(PWD);
            if (password == null) {
                if (debug) {
                    System.out.println
                        ("Password from shared state is null");
                }
                throw new LoginException
                    ("Password can not be obtained from sharedstate ");
            }
            if (debug) {
                System.out.println
                    ("password is " + new String(password));
            }
            return;
        }
        if (doNotPrompt) {
            throw new LoginException
                ("Unable to obtain password from user\n");
        } else {
            if (callbackHandler == null)
                throw new LoginException("No CallbackHandler "
                                         + "available "
                                         + "to garner authentication "
                                         + "information from the user");
            try {
                Callback[] callbacks = new Callback[1];
                String userName = krb5PrincName.toString();
                MessageFormat form = new MessageFormat(
                                         getAuthResourceString(
                                         "Kerberos.password.for.username."));
                Object[] source = {userName};
                callbacks[0] = new PasswordCallback(
                                                    form.format(source),
                                                    false);
                callbackHandler.handle(callbacks);
                char[] tmpPassword = ((PasswordCallback)
                                      callbacks[0]).getPassword();
                if (tmpPassword == null) {
                    throw new LoginException("No password provided");
                }
                password = new char[tmpPassword.length];
                System.arraycopy(tmpPassword, 0,
                                 password, 0, tmpPassword.length);
                ((PasswordCallback)callbacks[0]).clearPassword();


                // clear tmpPassword
                for (int i = 0; i < tmpPassword.length; i++)
                    tmpPassword[i] = ' ';
                tmpPassword = null;
                if (debug) {
                    System.out.println("\t\t[Krb5LoginModule] " +
                                       "user entered username: " +
                                       krb5PrincName);
                    System.out.println();
                }
            } catch (java.io.IOException ioe) {
                throw new LoginException(ioe.getMessage());
            } catch (UnsupportedCallbackException uce) {
                throw new LoginException(uce.getMessage()
                                         +" not available to garner "
                                         +" authentication information "
                                         + "from the user");
            }
        }
    }

    private void validateConfiguration() throws LoginException {
        if (doNotPrompt && !useTicketCache && !useKeyTab
                && !tryFirstPass && !useFirstPass)
            throw new LoginException
                ("Configuration Error"
                 + " - either doNotPrompt should be "
                 + " false or at least one of useTicketCache, "
                 + " useKeyTab, tryFirstPass and useFirstPass"
                 + " should be true");
        if (ticketCacheName != null && !useTicketCache)
            throw new LoginException
                ("Configuration Error "
                 + " - useTicketCache should be set "
                 + "to true to use the ticket cache"
                 + ticketCacheName);
        if (keyTabName != null & !useKeyTab)
            throw new LoginException
                ("Configuration Error - useKeyTab should be set to true "
                 + "to use the keytab" + keyTabName);
        if (storeKey && doNotPrompt && !useKeyTab
                && !tryFirstPass && !useFirstPass)
            throw new LoginException
                ("Configuration Error - either doNotPrompt should be set to "
                 + " false or at least one of tryFirstPass, useFirstPass "
                 + "or useKeyTab must be set to true for storeKey option");
        if (renewTGT && !useTicketCache)
            throw new LoginException
                ("Configuration Error"
                 + " - either useTicketCache should be "
                 + " true or renewTGT should be false");
        if (krb5PrincName != null && krb5PrincName.toString().equals("*")) {
            if (isInitiator) {
                throw new LoginException
                    ("Configuration Error"
                    + " - principal cannot be * when isInitiator is true");
            }
        }
    }

    private static boolean isCurrent(Credentials creds)
    {
        Date endTime = creds.getEndTime();
        if (endTime != null) {
            return (System.currentTimeMillis() <= endTime.getTime());
        }
        return true;
    }

    private static boolean isOld(Credentials creds)
    {
        Date endTime = creds.getEndTime();
        if (endTime != null) {
            Date authTime = creds.getAuthTime();
            long now = System.currentTimeMillis();
            if (authTime != null) {
                // pass the mid between auth and end
                return now - authTime.getTime() > endTime.getTime() - now;
            } else {
                // will expire in less than 2 hours
                return now <= endTime.getTime() - 1000*3600*2L;
            }
        }
        return false;
    }

    private Credentials renewCredentials(Credentials creds)
    {
        Credentials lcreds;
        try {
            if (!creds.isRenewable())
                throw new RefreshFailedException("This ticket" +
                                " is not renewable");
            if (creds.getRenewTill() == null) {
                // Renewable ticket without renew-till. Illegal and ignored.
                return creds;
            }
            if (System.currentTimeMillis() > cred.getRenewTill().getTime())
                throw new RefreshFailedException("This ticket is past "
                                             + "its last renewal time.");
            lcreds = creds.renew();
            if (debug)
                System.out.println("Renewed Kerberos Ticket");
        } catch (Exception e) {
            lcreds = null;
            if (debug)
                System.out.println("Ticket could not be renewed : "
                                + e.getMessage());
        }
        return lcreds;
    }

    
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 login method), then this method associates a Krb5Principal with the Subject located in the LoginModule. It adds Kerberos Credentials to the the Subject's private credentials set. If this LoginModule's own authentication attempted failed, then this method removes any state that was originally saved. 
Throws:
Returns:true if this LoginModule's own login and commit
         attempts succeeded, or false otherwise.
/**
     * This method is called if the LoginContext's
     * overall authentication succeeded
     * (the relevant REQUIRED, REQUISITE, SUFFICIENT and OPTIONAL
     * LoginModules succeeded).
     *
     * <p> If this LoginModule's own authentication attempt
     * succeeded (checked by retrieving the private state saved by the
     * {@code login} method), then this method associates a
     * {@code Krb5Principal}
     * with the {@code Subject} located in the
     * {@code LoginModule}. It adds Kerberos Credentials to the
     *  the Subject's private credentials set. 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 {

        /*
         * Let us add the Krb5 Creds to the Subject's
         * private credentials. The credentials are of type
         * KerberosKey or KerberosTicket
         */
        if (succeeded == false) {
            return false;
        } else {

            if (isInitiator && (cred == null)) {
                succeeded = false;
                throw new LoginException("Null Client Credential");
            }

            if (subject.isReadOnly()) {
                cleanKerberosCred();
                throw new LoginException("Subject is Readonly");
            }

            /*
             * Add the Principal (authenticated identity)
             * to the Subject's principal set and
             * add the credentials (TGT or Service key) to the
             * Subject's private credentials
             */

            Set<Object> privCredSet =  subject.getPrivateCredentials();
            Set<java.security.Principal> princSet  = subject.getPrincipals();
            kerbClientPrinc = new KerberosPrincipal(principal.getName());

            // create Kerberos Ticket
            if (isInitiator) {
                kerbTicket = Krb5Util.credsToTicket(cred);
                if (cred.getProxy() != null) {
                    KerberosSecrets.getJavaxSecurityAuthKerberosAccess()
                            .kerberosTicketSetProxy(kerbTicket,Krb5Util.credsToTicket(cred.getProxy()));
                }
            }

            if (storeKey && encKeys != null) {
                if (encKeys.length == 0) {
                    succeeded = false;
                    throw new LoginException("Null Server Key ");
                }

                kerbKeys = new KerberosKey[encKeys.length];
                for (int i = 0; i < encKeys.length; i ++) {
                    Integer temp = encKeys[i].getKeyVersionNumber();
                    kerbKeys[i] = new KerberosKey(kerbClientPrinc,
                                          encKeys[i].getBytes(),
                                          encKeys[i].getEType(),
                                          (temp == null?
                                          0: temp.intValue()));
                }

            }
            // Let us add the kerbClientPrinc,kerbTicket and KeyTab/KerbKey (if
            // storeKey is true)

            // We won't add "*" as a KerberosPrincipal
            if (!unboundServer &&
                    !princSet.contains(kerbClientPrinc)) {
                princSet.add(kerbClientPrinc);
            }

            // add the TGT
            if (kerbTicket != null) {
                if (!privCredSet.contains(kerbTicket))
                    privCredSet.add(kerbTicket);
            }

            if (storeKey) {
                if (encKeys == null) {
                    if (ktab != null) {
                        if (!privCredSet.contains(ktab)) {
                            privCredSet.add(ktab);
                        }
                    } else {
                        succeeded = false;
                        throw new LoginException("No key to store");
                    }
                } else {
                    for (int i = 0; i < kerbKeys.length; i ++) {
                        if (!privCredSet.contains(kerbKeys[i])) {
                            privCredSet.add(kerbKeys[i]);
                        }
                        encKeys[i].destroy();
                        encKeys[i] = null;
                        if (debug) {
                            System.out.println("Added server's key"
                                            + kerbKeys[i]);
                            System.out.println("\t\t[Krb5LoginModule] " +
                                           "added Krb5Principal  " +
                                           kerbClientPrinc.toString()
                                           + " to Subject");
                        }
                    }
                }
            }
        }
        commitSucceeded = true;
        if (debug)
            System.out.println("Commit Succeeded \n");
        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 login and commit methods), then this method cleans up any state that was originally saved. 
Throws:
Returns:false if this LoginModule's own login and/or commit attempts
         failed, and true otherwise.
/**
     * This method is called if the LoginContext's
     * overall authentication failed.
     * (the relevant REQUIRED, REQUISITE, SUFFICIENT and OPTIONAL
     * LoginModules did not succeed).
     *
     * <p> If this LoginModule's own authentication attempt
     * succeeded (checked by retrieving the private state saved by the
     * {@code login} and {@code commit} 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;
            cleanKerberosCred();
        } else {
            // overall authentication succeeded and commit succeeded,
            // but someone else's commit failed
            logout();
        }
        return true;
    }

    
Logout the user.

 This method removes the Krb5Principal that was added by the commit method. 
Throws:
Returns:true in all cases since this LoginModule should not be ignored.
/**
     * Logout the user.
     *
     * <p> This method removes the {@code Krb5Principal}
     * that was added by the {@code commit} method.
     *
     * @exception LoginException if the logout fails.
     *
     * @return true in all cases since this {@code LoginModule}
     *          should not be ignored.
     */
    public boolean logout() throws LoginException {

        if (debug) {
            System.out.println("\t\t[Krb5LoginModule]: " +
                "Entering logout");
        }

        if (subject.isReadOnly()) {
            cleanKerberosCred();
            throw new LoginException("Subject is Readonly");
        }

        subject.getPrincipals().remove(kerbClientPrinc);
           // Let us remove all Kerberos credentials stored in the Subject
        Iterator<Object> it = subject.getPrivateCredentials().iterator();
        while (it.hasNext()) {
            Object o = it.next();
            if (o instanceof KerberosTicket ||
                    o instanceof KerberosKey ||
                    o instanceof KeyTab) {
                it.remove();
            }
        }
        // clean the kerberos ticket and keys
        cleanKerberosCred();

        succeeded = false;
        commitSucceeded = false;
        if (debug) {
            System.out.println("\t\t[Krb5LoginModule]: " +
                               "logged out Subject");
        }
        return true;
    }

    
Clean Kerberos credentials

/**
     * Clean Kerberos credentials
     */
    private void cleanKerberosCred() throws LoginException {
        // Clean the ticket and server key
        try {
            if (kerbTicket != null)
                kerbTicket.destroy();
            if (kerbKeys != null) {
                for (int i = 0; i < kerbKeys.length; i++) {
                    kerbKeys[i].destroy();
                }
            }
        } catch (DestroyFailedException e) {
            throw new LoginException
                ("Destroy Failed on Kerberos Private Credentials");
        }
        kerbTicket = null;
        kerbKeys = null;
        kerbClientPrinc = null;
    }

    
Clean out the state

/**
     * Clean out the state
     */
    private void cleanState() {

        // save input as shared state only if
        // authentication succeeded
        if (succeeded) {
            if (storePass &&
                !sharedState.containsKey(NAME) &&
                !sharedState.containsKey(PWD)) {
                sharedState.put(NAME, username);
                sharedState.put(PWD, password);
            }
        } else {
            // remove temp results for the next try
            encKeys = null;
            ktab = null;
            principal = null;
        }
        username = null;
        password = null;
        if (krb5PrincName != null && krb5PrincName.length() != 0)
            krb5PrincName.delete(0, krb5PrincName.length());
        krb5PrincName = null;
        if (clearPass) {
            sharedState.remove(NAME);
            sharedState.remove(PWD);
        }
    }
}