com.buaa.cfs.security.UserGroupInformation.java Source code

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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE
 * file distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */
package com.buaa.cfs.security;

import com.buaa.cfs.common.oncrpc.security.Credentials;
import com.buaa.cfs.conf.Configuration;
import com.buaa.cfs.security.token.Token;
import com.buaa.cfs.security.token.TokenIdentifier;
import com.buaa.cfs.utils.KerberosUtil;
import com.buaa.cfs.utils.SecurityUtil;
import com.buaa.cfs.utils.Shell;
import com.buaa.cfs.utils.Time;
import com.buaa.cfs.constant.CommonConfigurationKeys;
import com.buaa.cfs.constant.CommonConfigurationKeysPublic;

import static com.buaa.cfs.constant.PlatformName.IBM_JAVA;

import com.google.common.annotations.VisibleForTesting;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.w3c.dom.Text;

import javax.security.auth.Subject;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.kerberos.KerberosPrincipal;
import javax.security.auth.kerberos.KerberosTicket;
import javax.security.auth.kerberos.KeyTab;
import javax.security.auth.login.AppConfigurationEntry;
import javax.security.auth.login.AppConfigurationEntry.LoginModuleControlFlag;
import javax.security.auth.login.LoginContext;
import javax.security.auth.login.LoginException;
import javax.security.auth.spi.LoginModule;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.File;
import java.io.IOException;
import java.lang.reflect.UndeclaredThrowableException;
import java.security.*;
import java.util.*;

/**
 * User and group information for Hadoop. This class wraps around a JAAS Subject and provides methods to determine the
 * user's username and groups. It supports both the Windows, Unix and Kerberos login modules.
 */
public class UserGroupInformation {
    private static final Log LOG = LogFactory.getLog(UserGroupInformation.class);
    /**
     * Percentage of the ticket window to use before we renew ticket.
     */
    private static final float TICKET_RENEW_WINDOW = 0.80f;
    private static boolean shouldRenewImmediatelyForTests = false;
    static final String HADOOP_USER_NAME = "HADOOP_USER_NAME";
    static final String HADOOP_PROXY_USER = "HADOOP_PROXY_USER";

    /**
     * For the purposes of unit tests, we want to test login from keytab and don't want to wait until the renew window
     * (controlled by TICKET_RENEW_WINDOW).
     *
     * @param immediate true if we should login without waiting for ticket window
     */
    //    @VisibleForTesting
    //    static void setShouldRenewImmediatelyForTests(boolean immediate) {
    //        shouldRenewImmediatelyForTests = immediate;
    //    }
    //
    //    /**
    //     * UgiMetrics maintains UGI activity statistics and publishes them through the metrics interfaces.
    //     */
    ////    @Metrics(about = "User and group related metrics", context = "ugi")
    //    static class UgiMetrics {
    ////        final MetricsRegistry registry = new MetricsRegistry("UgiMetrics");
    //
    //        //        @Metric("Rate of successful kerberos logins and latency (milliseconds)")
    //        MutableRate loginSuccess;
    //        //        @Metric("Rate of failed kerberos logins and latency (milliseconds)")
    //        MutableRate loginFailure;
    //        //        @Metric("GetGroups")
    //        MutableRate getGroups;
    //        MutableQuantiles[] getGroupsQuantiles;
    //
    //        static UgiMetrics create() {
    //            return DefaultMetricsSystem.instance().register(new UgiMetrics());
    //        }
    //
    //        void addGetGroups(long latency) {
    //            getGroups.add(latency);
    //            if (getGroupsQuantiles != null) {
    //                for (MutableQuantiles q : getGroupsQuantiles) {
    //                    q.add(latency);
    //                }
    //            }
    //        }
    //    }

    /**
     * A login module that looks at the Kerberos, Unix, or Windows principal and adds the corresponding UserName.
     */

    public static class HadoopLoginModule implements LoginModule {
        private Subject subject;

        @Override
        public boolean abort() throws LoginException {
            return true;
        }

        private <T extends Principal> T getCanonicalUser(Class<T> cls) {
            for (T user : subject.getPrincipals(cls)) {
                return user;
            }
            return null;
        }

        @Override
        public boolean commit() throws LoginException {
            if (LOG.isDebugEnabled()) {
                LOG.debug("hadoop login commit");
            }
            // if we already have a user, we are done.
            if (!subject.getPrincipals(User.class).isEmpty()) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("using existing subject:" + subject.getPrincipals());
                }
                return true;
            }
            Principal user = null;
            // if we are using kerberos, try it out
            if (isAuthenticationMethodEnabled(AuthenticationMethod.KERBEROS)) {
                user = getCanonicalUser(KerberosPrincipal.class);
                if (LOG.isDebugEnabled()) {
                    LOG.debug("using kerberos user:" + user);
                }
            }
            //If we don't have a kerberos user and security is disabled, check
            //if user is specified in the environment or properties
            if (!isSecurityEnabled() && (user == null)) {
                String envUser = System.getenv(HADOOP_USER_NAME);
                if (envUser == null) {
                    envUser = System.getProperty(HADOOP_USER_NAME);
                }
                user = envUser == null ? null : new User(envUser);
            }
            // use the OS user
            if (user == null) {
                user = getCanonicalUser(OS_PRINCIPAL_CLASS);
                if (LOG.isDebugEnabled()) {
                    LOG.debug("using local user:" + user);
                }
            }
            // if we found the user, add our principal
            if (user != null) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Using user: \"" + user + "\" with name " + user.getName());
                }

                User userEntry = null;
                try {
                    userEntry = new User(user.getName());
                } catch (Exception e) {
                    throw (LoginException) (new LoginException(e.toString()).initCause(e));
                }
                if (LOG.isDebugEnabled()) {
                    LOG.debug("User entry: \"" + userEntry.toString() + "\"");
                }

                subject.getPrincipals().add(userEntry);
                return true;
            }
            LOG.error("Can't find user in " + subject);
            throw new LoginException("Can't find user name");
        }

        @Override
        public void initialize(Subject subject, CallbackHandler callbackHandler, Map<String, ?> sharedState,
                Map<String, ?> options) {
            this.subject = subject;
        }

        @Override
        public boolean login() throws LoginException {
            if (LOG.isDebugEnabled()) {
                LOG.debug("hadoop login");
            }
            return true;
        }

        @Override
        public boolean logout() throws LoginException {
            if (LOG.isDebugEnabled()) {
                LOG.debug("hadoop logout");
            }
            return true;
        }
    }

    /** Metrics to track UGI activity */
    //    static UgiMetrics metrics = UgiMetrics.create();
    /** The auth method to use */
    private static AuthenticationMethod authenticationMethod;
    /** Server-side groups fetching service */
    private static Groups groups;
    /** The configuration to use */
    private static Configuration conf;

    /** Leave 10 minutes between relogin attempts. */
    private static final long MIN_TIME_BEFORE_RELOGIN = 10 * 60 * 1000L;

    /** Environment variable pointing to the token cache file */
    public static final String HADOOP_TOKEN_FILE_LOCATION = "HADOOP_TOKEN_FILE_LOCATION";

    /**
     * A method to initialize the fields that depend on a configuration. Must be called before useKerberos or groups is
     * used.
     */
    private static void ensureInitialized() {
        if (conf == null) {
            synchronized (UserGroupInformation.class) {
                if (conf == null) { // someone might have beat us
                    initialize(new Configuration(), false);
                }
            }
        }
    }

    /**
     * Initialize UGI and related classes.
     *
     * @param conf the configuration to use
     */
    private static synchronized void initialize(Configuration conf, boolean overrideNameRules) {
        authenticationMethod = SecurityUtil.getAuthenticationMethod(conf);
        if (overrideNameRules || !HadoopKerberosName.hasRulesBeenSet()) {
            try {
                HadoopKerberosName.setConfiguration(conf);
            } catch (IOException ioe) {
                throw new RuntimeException("Problem with Kerberos auth_to_local name configuration", ioe);
            }
        }
        // If we haven't set up testing groups, use the configuration to find it
        if (!(groups instanceof TestingGroups)) {
            groups = Groups.getUserToGroupsMappingService(conf);
        }
        UserGroupInformation.conf = conf;

        //        if (metrics.getGroupsQuantiles == null) {
        //            int[] intervals = conf.getInts(HADOOP_USER_GROUP_METRICS_PERCENTILES_INTERVALS);
        //            if (intervals != null && intervals.length > 0) {
        //                final int length = intervals.length;
        //                MutableQuantiles[] getGroupsQuantiles = new MutableQuantiles[length];
        //                for (int i = 0; i < length; i++) {
        //                    getGroupsQuantiles[i] = metrics.registry.newQuantiles(
        //                            "getGroups" + intervals[i] + "s",
        //                            "Get groups", "ops", "latency", intervals[i]);
        //                }
        //                metrics.getGroupsQuantiles = getGroupsQuantiles;
        //            }
        //        }
    }

    /**
     * Set the static configuration for UGI. In particular, set the security authentication mechanism and the group look
     * up service.
     *
     * @param conf the configuration to use
     */
    public static void setConfiguration(Configuration conf) {
        initialize(conf, true);
    }

    @VisibleForTesting
    static void reset() {
        authenticationMethod = null;
        conf = null;
        groups = null;
        setLoginUser(null);
        HadoopKerberosName.setRules(null);
    }

    /**
     * Determine if UserGroupInformation is using Kerberos to determine user identities or is relying on simple
     * authentication
     *
     * @return true if UGI is working in a secure environment
     */
    public static boolean isSecurityEnabled() {
        return !isAuthenticationMethodEnabled(AuthenticationMethod.SIMPLE);
    }

    private static boolean isAuthenticationMethodEnabled(AuthenticationMethod method) {
        ensureInitialized();
        return (authenticationMethod == method);
    }

    /**
     * Information about the logged in user.
     */
    private static UserGroupInformation loginUser = null;
    private static String keytabPrincipal = null;
    private static String keytabFile = null;

    private final Subject subject;
    // All non-static fields must be read-only caches that come from the subject.
    private final User user;
    private final boolean isKeytab;
    private final boolean isKrbTkt;

    private static String OS_LOGIN_MODULE_NAME;
    private static Class<? extends Principal> OS_PRINCIPAL_CLASS;

    private static final boolean windows = System.getProperty("os.name").startsWith("Windows");
    private static final boolean is64Bit = System.getProperty("os.arch").contains("64");
    private static final boolean aix = System.getProperty("os.name").equals("AIX");

    /* Return the OS login module class name */
    private static String getOSLoginModuleName() {
        if (IBM_JAVA) {
            if (windows) {
                return is64Bit ? "com.ibm.security.auth.module.Win64LoginModule"
                        : "com.ibm.security.auth.module.NTLoginModule";
            } else if (aix) {
                return is64Bit ? "com.ibm.security.auth.module.AIX64LoginModule"
                        : "com.ibm.security.auth.module.AIXLoginModule";
            } else {
                return "com.ibm.security.auth.module.LinuxLoginModule";
            }
        } else {
            return windows ? "com.sun.security.auth.module.NTLoginModule"
                    : "com.sun.security.auth.module.UnixLoginModule";
        }
    }

    /* Return the OS principal class */
    @SuppressWarnings("unchecked")
    private static Class<? extends Principal> getOsPrincipalClass() {
        ClassLoader cl = ClassLoader.getSystemClassLoader();
        try {
            String principalClass = null;
            if (IBM_JAVA) {
                if (is64Bit) {
                    principalClass = "com.ibm.security.auth.UsernamePrincipal";
                } else {
                    if (windows) {
                        principalClass = "com.ibm.security.auth.NTUserPrincipal";
                    } else if (aix) {
                        principalClass = "com.ibm.security.auth.AIXPrincipal";
                    } else {
                        principalClass = "com.ibm.security.auth.LinuxPrincipal";
                    }
                }
            } else {
                principalClass = windows ? "com.sun.security.auth.NTUserPrincipal"
                        : "com.sun.security.auth.UnixPrincipal";
            }
            return (Class<? extends Principal>) cl.loadClass(principalClass);
        } catch (ClassNotFoundException e) {
            LOG.error("Unable to find JAAS classes:" + e.getMessage());
        }
        return null;
    }

    static {
        OS_LOGIN_MODULE_NAME = getOSLoginModuleName();
        OS_PRINCIPAL_CLASS = getOsPrincipalClass();
    }

    private static class RealUser implements Principal {
        private final UserGroupInformation realUser;

        RealUser(UserGroupInformation realUser) {
            this.realUser = realUser;
        }

        @Override
        public String getName() {
            return realUser.getUserName();
        }

        public UserGroupInformation getRealUser() {
            return realUser;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            } else if (o == null || getClass() != o.getClass()) {
                return false;
            } else {
                return realUser.equals(((RealUser) o).realUser);
            }
        }

        @Override
        public int hashCode() {
            return realUser.hashCode();
        }

        @Override
        public String toString() {
            return realUser.toString();
        }
    }

    /**
     * A JAAS configuration that defines the login modules that we want to use for login.
     */
    private static class HadoopConfiguration extends javax.security.auth.login.Configuration {
        private static final String SIMPLE_CONFIG_NAME = "hadoop-simple";
        private static final String USER_KERBEROS_CONFIG_NAME = "hadoop-user-kerberos";
        private static final String KEYTAB_KERBEROS_CONFIG_NAME = "hadoop-keytab-kerberos";

        private static final Map<String, String> BASIC_JAAS_OPTIONS = new HashMap<String, String>();

        static {
            String jaasEnvVar = System.getenv("HADOOP_JAAS_DEBUG");
            if (jaasEnvVar != null && "true".equalsIgnoreCase(jaasEnvVar)) {
                BASIC_JAAS_OPTIONS.put("debug", "true");
            }
        }

        private static final AppConfigurationEntry OS_SPECIFIC_LOGIN = new AppConfigurationEntry(
                OS_LOGIN_MODULE_NAME, LoginModuleControlFlag.REQUIRED, BASIC_JAAS_OPTIONS);
        private static final AppConfigurationEntry HADOOP_LOGIN = new AppConfigurationEntry(
                HadoopLoginModule.class.getName(), LoginModuleControlFlag.REQUIRED, BASIC_JAAS_OPTIONS);
        private static final Map<String, String> USER_KERBEROS_OPTIONS = new HashMap<String, String>();

        static {
            if (IBM_JAVA) {
                USER_KERBEROS_OPTIONS.put("useDefaultCcache", "true");
            } else {
                USER_KERBEROS_OPTIONS.put("doNotPrompt", "true");
                USER_KERBEROS_OPTIONS.put("useTicketCache", "true");
            }
            String ticketCache = System.getenv("KRB5CCNAME");
            if (ticketCache != null) {
                if (IBM_JAVA) {
                    // The first value searched when "useDefaultCcache" is used.
                    System.setProperty("KRB5CCNAME", ticketCache);
                } else {
                    USER_KERBEROS_OPTIONS.put("ticketCache", ticketCache);
                }
            }
            USER_KERBEROS_OPTIONS.put("renewTGT", "true");
            USER_KERBEROS_OPTIONS.putAll(BASIC_JAAS_OPTIONS);
        }

        private static final AppConfigurationEntry USER_KERBEROS_LOGIN = new AppConfigurationEntry(
                KerberosUtil.getKrb5LoginModuleName(), LoginModuleControlFlag.OPTIONAL, USER_KERBEROS_OPTIONS);
        private static final Map<String, String> KEYTAB_KERBEROS_OPTIONS = new HashMap<String, String>();

        static {
            if (IBM_JAVA) {
                KEYTAB_KERBEROS_OPTIONS.put("credsType", "both");
            } else {
                KEYTAB_KERBEROS_OPTIONS.put("doNotPrompt", "true");
                KEYTAB_KERBEROS_OPTIONS.put("useKeyTab", "true");
                KEYTAB_KERBEROS_OPTIONS.put("storeKey", "true");
            }
            KEYTAB_KERBEROS_OPTIONS.put("refreshKrb5Config", "true");
            KEYTAB_KERBEROS_OPTIONS.putAll(BASIC_JAAS_OPTIONS);
        }

        private static final AppConfigurationEntry KEYTAB_KERBEROS_LOGIN = new AppConfigurationEntry(
                KerberosUtil.getKrb5LoginModuleName(), LoginModuleControlFlag.REQUIRED, KEYTAB_KERBEROS_OPTIONS);

        private static final AppConfigurationEntry[] SIMPLE_CONF = new AppConfigurationEntry[] { OS_SPECIFIC_LOGIN,
                HADOOP_LOGIN };

        private static final AppConfigurationEntry[] USER_KERBEROS_CONF = new AppConfigurationEntry[] {
                OS_SPECIFIC_LOGIN, USER_KERBEROS_LOGIN, HADOOP_LOGIN };

        private static final AppConfigurationEntry[] KEYTAB_KERBEROS_CONF = new AppConfigurationEntry[] {
                KEYTAB_KERBEROS_LOGIN, HADOOP_LOGIN };

        @Override
        public AppConfigurationEntry[] getAppConfigurationEntry(String appName) {
            if (SIMPLE_CONFIG_NAME.equals(appName)) {
                return SIMPLE_CONF;
            } else if (USER_KERBEROS_CONFIG_NAME.equals(appName)) {
                return USER_KERBEROS_CONF;
            } else if (KEYTAB_KERBEROS_CONFIG_NAME.equals(appName)) {
                if (IBM_JAVA) {
                    KEYTAB_KERBEROS_OPTIONS.put("useKeytab", prependFileAuthority(keytabFile));
                } else {
                    KEYTAB_KERBEROS_OPTIONS.put("keyTab", keytabFile);
                }
                KEYTAB_KERBEROS_OPTIONS.put("principal", keytabPrincipal);
                return KEYTAB_KERBEROS_CONF;
            }
            return null;
        }
    }

    private static String prependFileAuthority(String keytabPath) {
        return keytabPath.startsWith("file://") ? keytabPath : "file://" + keytabPath;
    }

    /**
     * Represents a javax.security configuration that is created at runtime.
     */
    private static class DynamicConfiguration extends javax.security.auth.login.Configuration {
        private AppConfigurationEntry[] ace;

        DynamicConfiguration(AppConfigurationEntry[] ace) {
            this.ace = ace;
        }

        @Override
        public AppConfigurationEntry[] getAppConfigurationEntry(String appName) {
            return ace;
        }
    }

    private static LoginContext newLoginContext(String appName, Subject subject,
            javax.security.auth.login.Configuration loginConf) throws LoginException {
        // Temporarily switch the thread's ContextClassLoader to match this
        // class's classloader, so that we can properly load HadoopLoginModule
        // from the JAAS libraries.
        Thread t = Thread.currentThread();
        ClassLoader oldCCL = t.getContextClassLoader();
        t.setContextClassLoader(HadoopLoginModule.class.getClassLoader());
        try {
            return new LoginContext(appName, subject, null, loginConf);
        } finally {
            t.setContextClassLoader(oldCCL);
        }
    }

    private LoginContext getLogin() {
        return user.getLogin();
    }

    private void setLogin(LoginContext login) {
        user.setLogin(login);
    }

    /**
     * Create a UserGroupInformation for the given subject. This does not change the subject or acquire new
     * credentials.
     *
     * @param subject the user's subject
     */
    UserGroupInformation(Subject subject) {
        this.subject = subject;
        this.user = subject.getPrincipals(User.class).iterator().next();
        this.isKeytab = !subject.getPrivateCredentials(KeyTab.class).isEmpty();
        this.isKrbTkt = !subject.getPrivateCredentials(KerberosTicket.class).isEmpty();
    }

    /**
     * checks if logged in using kerberos
     *
     * @return true if the subject logged via keytab or has a Kerberos TGT
     */
    public boolean hasKerberosCredentials() {
        return isKeytab || isKrbTkt;
    }

    /**
     * Return the current user, including any doAs in the current stack.
     *
     * @return the current user
     *
     * @throws IOException if login fails
     */

    public synchronized static UserGroupInformation getCurrentUser() throws IOException {
        AccessControlContext context = AccessController.getContext();
        Subject subject = Subject.getSubject(context);
        if (subject == null || subject.getPrincipals(User.class).isEmpty()) {
            return getLoginUser();
        } else {
            return new UserGroupInformation(subject);
        }
    }

    /**
     * Find the most appropriate UserGroupInformation to use
     *
     * @param ticketCachePath The Kerberos ticket cache path, or NULL if none is specfied
     * @param user            The user name, or NULL if none is specified.
     *
     * @return The most appropriate UserGroupInformation
     */
    public static UserGroupInformation getBestUGI(String ticketCachePath, String user) throws IOException {
        if (ticketCachePath != null) {
            return getUGIFromTicketCache(ticketCachePath, user);
        } else if (user == null) {
            return getCurrentUser();
        } else {
            return createRemoteUser(user);
        }
    }

    /**
     * Create a UserGroupInformation from a Kerberos ticket cache.
     *
     * @param user The principal name to load from the ticket cache
     *
     * @throws IOException if the kerberos login fails
     */

    public static UserGroupInformation getUGIFromTicketCache(String ticketCache, String user) throws IOException {
        if (!isAuthenticationMethodEnabled(AuthenticationMethod.KERBEROS)) {
            return getBestUGI(null, user);
        }
        try {
            Map<String, String> krbOptions = new HashMap<String, String>();
            if (IBM_JAVA) {
                krbOptions.put("useDefaultCcache", "true");
                // The first value searched when "useDefaultCcache" is used.
                System.setProperty("KRB5CCNAME", ticketCache);
            } else {
                krbOptions.put("doNotPrompt", "true");
                krbOptions.put("useTicketCache", "true");
                krbOptions.put("useKeyTab", "false");
                krbOptions.put("ticketCache", ticketCache);
            }
            krbOptions.put("renewTGT", "false");
            krbOptions.putAll(HadoopConfiguration.BASIC_JAAS_OPTIONS);
            AppConfigurationEntry ace = new AppConfigurationEntry(KerberosUtil.getKrb5LoginModuleName(),
                    LoginModuleControlFlag.REQUIRED, krbOptions);
            DynamicConfiguration dynConf = new DynamicConfiguration(new AppConfigurationEntry[] { ace });
            LoginContext login = newLoginContext(HadoopConfiguration.USER_KERBEROS_CONFIG_NAME, null, dynConf);
            login.login();

            Subject loginSubject = login.getSubject();
            Set<Principal> loginPrincipals = loginSubject.getPrincipals();
            if (loginPrincipals.isEmpty()) {
                throw new RuntimeException("No login principals found!");
            }
            if (loginPrincipals.size() != 1) {
                LOG.warn("found more than one principal in the ticket cache file " + ticketCache);
            }
            User ugiUser = new User(loginPrincipals.iterator().next().getName(), AuthenticationMethod.KERBEROS,
                    login);
            loginSubject.getPrincipals().add(ugiUser);
            UserGroupInformation ugi = new UserGroupInformation(loginSubject);
            ugi.setLogin(login);
            ugi.setAuthenticationMethod(AuthenticationMethod.KERBEROS);
            return ugi;
        } catch (LoginException le) {
            throw new IOException("failure to login using ticket cache file " + ticketCache, le);
        }
    }

    /**
     * Create a UserGroupInformation from a Subject with Kerberos principal.
     *
     * @throws IOException if the kerberos login fails
     */
    public static UserGroupInformation getUGIFromSubject(Subject subject) throws IOException {
        if (subject == null) {
            throw new IOException("Subject must not be null");
        }

        if (subject.getPrincipals(KerberosPrincipal.class).isEmpty()) {
            throw new IOException("Provided Subject must contain a KerberosPrincipal");
        }

        KerberosPrincipal principal = subject.getPrincipals(KerberosPrincipal.class).iterator().next();

        User ugiUser = new User(principal.getName(), AuthenticationMethod.KERBEROS, null);
        subject.getPrincipals().add(ugiUser);
        UserGroupInformation ugi = new UserGroupInformation(subject);
        ugi.setLogin(null);
        ugi.setAuthenticationMethod(AuthenticationMethod.KERBEROS);
        return ugi;
    }

    /**
     * Get the currently logged in user.
     *
     * @return the logged in user
     *
     * @throws IOException if login fails
     */

    public synchronized static UserGroupInformation getLoginUser() throws IOException {
        if (loginUser == null) {
            loginUserFromSubject(null);
        }
        return loginUser;
    }

    /**
     * remove the login method that is followed by a space from the username e.g. "jack (auth:SIMPLE)" -> "jack"
     *
     * @param userName
     *
     * @return userName without login method
     */
    public static String trimLoginMethod(String userName) {
        int spaceIndex = userName.indexOf(' ');
        if (spaceIndex >= 0) {
            userName = userName.substring(0, spaceIndex);
        }
        return userName;
    }

    /**
     * Log in a user using the given subject
     *
     * @throws IOException if login fails
     * @parma subject the subject to use when logging in a user, or null to create a new subject.
     */

    public synchronized static void loginUserFromSubject(Subject subject) throws IOException {
        ensureInitialized();
        try {
            if (subject == null) {
                subject = new Subject();
            }
            LoginContext login = newLoginContext(authenticationMethod.getLoginAppName(), subject,
                    new HadoopConfiguration());
            login.login();
            UserGroupInformation realUser = new UserGroupInformation(subject);
            realUser.setLogin(login);
            realUser.setAuthenticationMethod(authenticationMethod);
            realUser = new UserGroupInformation(login.getSubject());
            // If the HADOOP_PROXY_USER environment variable or property
            // is specified, create a proxy user as the logged in user.
            String proxyUser = System.getenv(HADOOP_PROXY_USER);
            if (proxyUser == null) {
                proxyUser = System.getProperty(HADOOP_PROXY_USER);
            }
            loginUser = proxyUser == null ? realUser : createProxyUser(proxyUser, realUser);

            String fileLocation = System.getenv(HADOOP_TOKEN_FILE_LOCATION);
            if (fileLocation != null) {
                // Load the token storage file and put all of the tokens into the
                // user. Don't use the FileSystem API for reading since it has a lock
                // cycle (HADOOP-9212).
                //                Credentials cred = Credentials.readTokenStorageFile(
                //                        new File(fileLocation), conf);
                //                loginUser.addCredentials(cred);
            }
            loginUser.spawnAutoRenewalThreadForUserCreds();
        } catch (LoginException le) {
            LOG.debug("failure to login", le);
            throw new IOException("failure to login", le);
        }
        if (LOG.isDebugEnabled()) {
            LOG.debug("UGI loginUser:" + loginUser);
        }
    }

    @VisibleForTesting
    public synchronized static void setLoginUser(UserGroupInformation ugi) {
        // if this is to become stable, should probably logout the currently
        // logged in ugi if it's different
        loginUser = ugi;
    }

    /**
     * Is this user logged in from a keytab file?
     *
     * @return true if the credentials are from a keytab file.
     */
    public boolean isFromKeytab() {
        return isKeytab;
    }

    /**
     * Get the Kerberos TGT
     *
     * @return the user's TGT or null if none was found
     */
    private synchronized KerberosTicket getTGT() {
        Set<KerberosTicket> tickets = subject.getPrivateCredentials(KerberosTicket.class);
        for (KerberosTicket ticket : tickets) {
            if (SecurityUtil.isOriginalTGT(ticket)) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Found tgt " + ticket);
                }
                return ticket;
            }
        }
        return null;
    }

    private long getRefreshTime(KerberosTicket tgt) {
        long start = tgt.getStartTime().getTime();
        long end = tgt.getEndTime().getTime();
        return start + (long) ((end - start) * TICKET_RENEW_WINDOW);
    }

    /** Spawn a thread to do periodic renewals of kerberos credentials */
    private void spawnAutoRenewalThreadForUserCreds() {
        if (isSecurityEnabled()) {
            //spawn thread only if we have kerb credentials
            if (user.getAuthenticationMethod() == AuthenticationMethod.KERBEROS && !isKeytab) {
                Thread t = new Thread(new Runnable() {

                    @Override
                    public void run() {
                        String cmd = conf.get("hadoop.kerberos.kinit.command", "kinit");
                        KerberosTicket tgt = getTGT();
                        if (tgt == null) {
                            return;
                        }
                        long nextRefresh = getRefreshTime(tgt);
                        while (true) {
                            try {
                                long now = Time.now();
                                if (LOG.isDebugEnabled()) {
                                    LOG.debug("Current time is " + now);
                                    LOG.debug("Next refresh is " + nextRefresh);
                                }
                                if (now < nextRefresh) {
                                    Thread.sleep(nextRefresh - now);
                                }
                                Shell.execCommand(cmd, "-R");
                                if (LOG.isDebugEnabled()) {
                                    LOG.debug("renewed ticket");
                                }
                                reloginFromTicketCache();
                                tgt = getTGT();
                                if (tgt == null) {
                                    LOG.warn("No TGT after renewal. Aborting renew thread for " + getUserName());
                                    return;
                                }
                                nextRefresh = Math.max(getRefreshTime(tgt), now + MIN_TIME_BEFORE_RELOGIN);
                            } catch (InterruptedException ie) {
                                LOG.warn("Terminating renewal thread");
                                return;
                            } catch (IOException ie) {
                                LOG.warn("Exception encountered while running the"
                                        + " renewal command. Aborting renew thread. " + ie);
                                return;
                            }
                        }
                    }
                });
                t.setDaemon(true);
                t.setName("TGT Renewer for " + getUserName());
                t.start();
            }
        }
    }

    /**
     * Log a user in from a keytab file. Loads a user identity from a keytab file and logs them in. They become the
     * currently logged-in user.
     *
     * @param user the principal name to load from the keytab
     * @param path the path to the keytab file
     *
     * @throws IOException if the keytab file can't be read
     */

    public synchronized static void loginUserFromKeytab(String user, String path) throws IOException {
        if (!isSecurityEnabled())
            return;

        keytabFile = path;
        keytabPrincipal = user;
        Subject subject = new Subject();
        LoginContext login;
        long start = 0;
        try {
            login = newLoginContext(HadoopConfiguration.KEYTAB_KERBEROS_CONFIG_NAME, subject,
                    new HadoopConfiguration());
            start = Time.now();
            login.login();
            //            metrics.loginSuccess.add(Time.now() - start);
            loginUser = new UserGroupInformation(subject);
            loginUser.setLogin(login);
            loginUser.setAuthenticationMethod(AuthenticationMethod.KERBEROS);
        } catch (LoginException le) {
            if (start > 0) {
                //                metrics.loginFailure.add(Time.now() - start);
            }
            throw new IOException("Login failure for " + user + " from keytab " + path + ": " + le, le);
        }
        LOG.info("Login successful for user " + keytabPrincipal + " using keytab file " + keytabFile);
    }

    /**
     * Re-login a user from keytab if TGT is expired or is close to expiry.
     *
     * @throws IOException
     */
    public synchronized void checkTGTAndReloginFromKeytab() throws IOException {
        if (!isSecurityEnabled() || user.getAuthenticationMethod() != AuthenticationMethod.KERBEROS || !isKeytab)
            return;
        KerberosTicket tgt = getTGT();
        if (tgt != null && !shouldRenewImmediatelyForTests && Time.now() < getRefreshTime(tgt)) {
            return;
        }
        reloginFromKeytab();
    }

    /**
     * Re-Login a user in from a keytab file. Loads a user identity from a keytab file and logs them in. They become the
     * currently logged-in user. This method assumes that {@link #loginUserFromKeytab(String, String)} had happened
     * already. The Subject field of this UserGroupInformation object is updated to have the new credentials.
     *
     * @throws IOException on a failure
     */

    public synchronized void reloginFromKeytab() throws IOException {
        if (!isSecurityEnabled() || user.getAuthenticationMethod() != AuthenticationMethod.KERBEROS || !isKeytab)
            return;

        long now = Time.now();
        if (!shouldRenewImmediatelyForTests && !hasSufficientTimeElapsed(now)) {
            return;
        }

        KerberosTicket tgt = getTGT();
        //Return if TGT is valid and is not going to expire soon.
        if (tgt != null && !shouldRenewImmediatelyForTests && now < getRefreshTime(tgt)) {
            return;
        }

        LoginContext login = getLogin();
        if (login == null || keytabFile == null) {
            throw new IOException("loginUserFromKeyTab must be done first");
        }

        long start = 0;
        // register most recent relogin attempt
        user.setLastLogin(now);
        try {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Initiating logout for " + getUserName());
            }
            synchronized (UserGroupInformation.class) {
                // clear up the kerberos state. But the tokens are not cleared! As per
                // the Java kerberos login module code, only the kerberos credentials
                // are cleared
                login.logout();
                // login and also update the subject field of this instance to
                // have the new credentials (pass it to the LoginContext constructor)
                login = newLoginContext(HadoopConfiguration.KEYTAB_KERBEROS_CONFIG_NAME, getSubject(),
                        new HadoopConfiguration());
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Initiating re-login for " + keytabPrincipal);
                }
                start = Time.now();
                login.login();
                //                metrics.loginSuccess.add(Time.now() - start);
                setLogin(login);
            }
        } catch (LoginException le) {
            if (start > 0) {
                //                metrics.loginFailure.add(Time.now() - start);
            }
            throw new IOException("Login failure for " + keytabPrincipal + " from keytab " + keytabFile, le);
        }
    }

    /**
     * Re-Login a user in from the ticket cache.  This method assumes that login had happened already. The Subject field
     * of this UserGroupInformation object is updated to have the new credentials.
     *
     * @throws IOException on a failure
     */

    public synchronized void reloginFromTicketCache() throws IOException {
        if (!isSecurityEnabled() || user.getAuthenticationMethod() != AuthenticationMethod.KERBEROS || !isKrbTkt)
            return;
        LoginContext login = getLogin();
        if (login == null) {
            throw new IOException("login must be done first");
        }
        long now = Time.now();
        if (!hasSufficientTimeElapsed(now)) {
            return;
        }
        // register most recent relogin attempt
        user.setLastLogin(now);
        try {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Initiating logout for " + getUserName());
            }
            //clear up the kerberos state. But the tokens are not cleared! As per
            //the Java kerberos login module code, only the kerberos credentials
            //are cleared
            login.logout();
            //login and also update the subject field of this instance to
            //have the new credentials (pass it to the LoginContext constructor)
            login = newLoginContext(HadoopConfiguration.USER_KERBEROS_CONFIG_NAME, getSubject(),
                    new HadoopConfiguration());
            if (LOG.isDebugEnabled()) {
                LOG.debug("Initiating re-login for " + getUserName());
            }
            login.login();
            setLogin(login);
        } catch (LoginException le) {
            throw new IOException("Login failure for " + getUserName(), le);
        }
    }

    /**
     * Log a user in from a keytab file. Loads a user identity from a keytab file and login them in. This new user does
     * not affect the currently logged-in user.
     *
     * @param user the principal name to load from the keytab
     * @param path the path to the keytab file
     *
     * @throws IOException if the keytab file can't be read
     */
    public synchronized static UserGroupInformation loginUserFromKeytabAndReturnUGI(String user, String path)
            throws IOException {
        if (!isSecurityEnabled())
            return UserGroupInformation.getCurrentUser();
        String oldKeytabFile = null;
        String oldKeytabPrincipal = null;

        long start = 0;
        try {
            oldKeytabFile = keytabFile;
            oldKeytabPrincipal = keytabPrincipal;
            keytabFile = path;
            keytabPrincipal = user;
            Subject subject = new Subject();

            LoginContext login = newLoginContext(HadoopConfiguration.KEYTAB_KERBEROS_CONFIG_NAME, subject,
                    new HadoopConfiguration());

            start = Time.now();
            login.login();
            //            metrics.loginSuccess.add(Time.now() - start);
            UserGroupInformation newLoginUser = new UserGroupInformation(subject);
            newLoginUser.setLogin(login);
            newLoginUser.setAuthenticationMethod(AuthenticationMethod.KERBEROS);

            return newLoginUser;
        } catch (LoginException le) {
            if (start > 0) {
                //                metrics.loginFailure.add(Time.now() - start);
            }
            throw new IOException("Login failure for " + user + " from keytab " + path, le);
        } finally {
            if (oldKeytabFile != null)
                keytabFile = oldKeytabFile;
            if (oldKeytabPrincipal != null)
                keytabPrincipal = oldKeytabPrincipal;
        }
    }

    private boolean hasSufficientTimeElapsed(long now) {
        if (now - user.getLastLogin() < MIN_TIME_BEFORE_RELOGIN) {
            LOG.warn("Not attempting to re-login since the last re-login was " + "attempted less than "
                    + (MIN_TIME_BEFORE_RELOGIN / 1000) + " seconds" + " before.");
            return false;
        }
        return true;
    }

    /**
     * Did the login happen via keytab
     *
     * @return true or false
     */

    public synchronized static boolean isLoginKeytabBased() throws IOException {
        return getLoginUser().isKeytab;
    }

    /**
     * Did the login happen via ticket cache
     *
     * @return true or false
     */
    public static boolean isLoginTicketBased() throws IOException {
        return getLoginUser().isKrbTkt;
    }

    /**
     * Create a user from a login name. It is intended to be used for remote users in RPC, since it won't have any
     * credentials.
     *
     * @param user the full user principal name, must not be empty or null
     *
     * @return the UserGroupInformation for the remote user.
     */

    public static UserGroupInformation createRemoteUser(String user) {
        //        return createRemoteUser(user, AuthMethod.SIMPLE);
        return null;
    }

    /**
     * Create a user from a login name. It is intended to be used for remote users in RPC, since it won't have any
     * credentials.
     *
     * @param user the full user principal name, must not be empty or null
     *
     * @return the UserGroupInformation for the remote user.
     */

    //    public static UserGroupInformation createRemoteUser(String user, AuthMethod authMethod) {
    //        if (user == null || user.isEmpty()) {
    //            throw new IllegalArgumentException("Null user");
    //        }
    //        Subject subject = new Subject();
    //        subject.getPrincipals().add(new User(user));
    //        UserGroupInformation result = new UserGroupInformation(subject);
    //        result.setAuthenticationMethod(authMethod);
    //        return result;
    //    }

    /**
     * existing types of authentications' methods
     */

    public static enum AuthMethod {
        SIMPLE((byte) 80, ""), KERBEROS((byte) 81, "GSSAPI"), @Deprecated
        DIGEST((byte) 82, "DIGEST-MD5"), TOKEN((byte) 82, "DIGEST-MD5"), PLAIN((byte) 83, "PLAIN");

        /** The code for this method. */
        public final byte code;
        public final String mechanismName;

        private AuthMethod(byte code, String mechanismName) {
            this.code = code;
            this.mechanismName = mechanismName;
        }

        private static final int FIRST_CODE = values()[0].code;

        /** Return the object represented by the code. */
        private static AuthMethod valueOf(byte code) {
            final int i = (code & 0xff) - FIRST_CODE;
            return i < 0 || i >= values().length ? null : values()[i];
        }

        /** Return the SASL mechanism name */
        public String getMechanismName() {
            return mechanismName;
        }

        /** Read from in */
        public static AuthMethod read(DataInput in) throws IOException {
            return valueOf(in.readByte());
        }

        /** Write to out */
        public void write(DataOutput out) throws IOException {
            out.write(code);
        }
    }

    ;

    public static enum AuthenticationMethod {
        // currently we support only one auth per method, but eventually a
        // subtype is needed to differentiate, ex. if digest is token or ldap
        SIMPLE(AuthMethod.SIMPLE, HadoopConfiguration.SIMPLE_CONFIG_NAME), KERBEROS(AuthMethod.KERBEROS,
                HadoopConfiguration.USER_KERBEROS_CONFIG_NAME), TOKEN(
                        AuthMethod.TOKEN), CERTIFICATE(null), KERBEROS_SSL(null), PROXY(null);

        private final AuthMethod authMethod;
        private final String loginAppName;

        private AuthenticationMethod(AuthMethod authMethod) {
            this(authMethod, null);
        }

        private AuthenticationMethod(AuthMethod authMethod, String loginAppName) {
            this.authMethod = authMethod;
            this.loginAppName = loginAppName;
        }

        public AuthMethod getAuthMethod() {
            return authMethod;
        }

        String getLoginAppName() {
            if (loginAppName == null) {
                throw new UnsupportedOperationException(this + " login authentication is not supported");
            }
            return loginAppName;
        }

        public static AuthenticationMethod valueOf(AuthMethod authMethod) {
            for (AuthenticationMethod value : values()) {
                if (value.getAuthMethod() == authMethod) {
                    return value;
                }
            }
            throw new IllegalArgumentException("no authentication method for " + authMethod);
        }
    }

    ;

    /**
     * Create a proxy user using username of the effective user and the ugi of the real user.
     *
     * @param user
     * @param realUser
     *
     * @return proxyUser ugi
     */

    public static UserGroupInformation createProxyUser(String user, UserGroupInformation realUser) {
        if (user == null || user.isEmpty()) {
            throw new IllegalArgumentException("Null user");
        }
        if (realUser == null) {
            throw new IllegalArgumentException("Null real user");
        }
        Subject subject = new Subject();
        Set<Principal> principals = subject.getPrincipals();
        principals.add(new User(user));
        principals.add(new RealUser(realUser));
        UserGroupInformation result = new UserGroupInformation(subject);
        result.setAuthenticationMethod(AuthenticationMethod.PROXY);
        return result;
    }

    /**
     * get RealUser (vs. EffectiveUser)
     *
     * @return realUser running over proxy user
     */

    public UserGroupInformation getRealUser() {
        for (RealUser p : subject.getPrincipals(RealUser.class)) {
            return p.getRealUser();
        }
        return null;
    }

    /**
     * This class is used for storing the groups for testing. It stores a local map that has the translation of
     * usernames to groups.
     */
    private static class TestingGroups extends Groups {
        private final Map<String, List<String>> userToGroupsMapping = new HashMap<String, List<String>>();
        private Groups underlyingImplementation;

        private TestingGroups(Groups underlyingImplementation) {
            super(new Configuration());
            this.underlyingImplementation = underlyingImplementation;
        }

        @Override
        public List<String> getGroups(String user) throws IOException {
            List<String> result = userToGroupsMapping.get(user);

            if (result == null) {
                result = underlyingImplementation.getGroups(user);
            }

            return result;
        }

        private void setUserGroups(String user, String[] groups) {
            userToGroupsMapping.put(user, Arrays.asList(groups));
        }
    }

    /**
     * Create a UGI for testing HDFS and MapReduce
     *
     * @param user       the full user principal name
     * @param userGroups the names of the groups that the user belongs to
     *
     * @return a fake user for running unit tests
     */

    public static UserGroupInformation createUserForTesting(String user, String[] userGroups) {
        ensureInitialized();
        UserGroupInformation ugi = createRemoteUser(user);
        // make sure that the testing object is setup
        if (!(groups instanceof TestingGroups)) {
            groups = new TestingGroups(groups);
        }
        // add the user groups
        ((TestingGroups) groups).setUserGroups(ugi.getShortUserName(), userGroups);
        return ugi;
    }

    /**
     * Create a proxy user UGI for testing HDFS and MapReduce
     *
     * @param user       the full user principal name for effective user
     * @param realUser   UGI of the real user
     * @param userGroups the names of the groups that the user belongs to
     *
     * @return a fake user for running unit tests
     */
    public static UserGroupInformation createProxyUserForTesting(String user, UserGroupInformation realUser,
            String[] userGroups) {
        ensureInitialized();
        UserGroupInformation ugi = createProxyUser(user, realUser);
        // make sure that the testing object is setup
        if (!(groups instanceof TestingGroups)) {
            groups = new TestingGroups(groups);
        }
        // add the user groups
        ((TestingGroups) groups).setUserGroups(ugi.getShortUserName(), userGroups);
        return ugi;
    }

    /**
     * Get the user's login name.
     *
     * @return the user's name up to the first '/' or '@'.
     */
    public String getShortUserName() {
        for (User p : subject.getPrincipals(User.class)) {
            return p.getShortName();
        }
        return null;
    }

    public String getPrimaryGroupName() throws IOException {
        String[] groups = getGroupNames();
        if (groups.length == 0) {
            throw new IOException("There is no primary group for UGI " + this);
        }
        return groups[0];
    }

    /**
     * Get the user's full principal name.
     *
     * @return the user's full principal name.
     */

    public String getUserName() {
        return user.getName();
    }

    /**
     * Add a TokenIdentifier to this UGI. The TokenIdentifier has typically been authenticated by the RPC layer as
     * belonging to the user represented by this UGI.
     *
     * @param tokenId tokenIdentifier to be added
     *
     * @return true on successful add of new tokenIdentifier
     */
    public synchronized boolean addTokenIdentifier(TokenIdentifier tokenId) {
        return subject.getPublicCredentials().add(tokenId);
    }

    /**
     * Get the set of TokenIdentifiers belonging to this UGI
     *
     * @return the set of TokenIdentifiers belonging to this UGI
     */
    public synchronized Set<TokenIdentifier> getTokenIdentifiers() {
        return subject.getPublicCredentials(TokenIdentifier.class);
    }

    /**
     * Add a token to this UGI
     *
     * @param token Token to be added
     *
     * @return true on successful add of new token
     */
    public boolean addToken(Token<? extends TokenIdentifier> token) {
        //        return (token != null) ? addToken(token.getService(), token) : false;
        return false;
    }

    /**
     * Add a named token to this UGI
     *
     * @param alias Name of the token
     * @param token Token to be added
     *
     * @return true on successful add of new token
     */
    public boolean addToken(Text alias, Token<? extends TokenIdentifier> token) {
        synchronized (subject) {
            //            getCredentialsInternal().addToken(alias, token);
            return true;
        }
    }

    /**
     * Obtain the collection of tokens associated with this user.
     *
     * @return an unmodifiable collection of tokens associated with user
     */
    public Collection<Token<? extends TokenIdentifier>> getTokens() {
        synchronized (subject) {
            //            return Collections.unmodifiableCollection(
            //                    new ArrayList<Token<?>>(getCredentialsInternal().getAllTokens()));
        }
        return null;
    }

    /**
     * Obtain the tokens in credentials form associated with this user.
     *
     * @return Credentials of tokens associated with this user
     */
    public Credentials getCredentials() {
        synchronized (subject) {
            //            Credentials creds = new Credentials(getCredentialsInternal());
            //            Iterator<Token<?>> iter = creds.getAllTokens().iterator();
            //            while (iter.hasNext()) {
            //                if (iter.next() instanceof Token.PrivateToken) {
            //                    iter.remove();
            //                }
            //            }
            //            return creds;
        }
        return null;
    }

    /**
     * Add the given Credentials to this user.
     *
     * @param credentials of tokens and secrets
     */
    public void addCredentials(Credentials credentials) {
        synchronized (subject) {
            //            getCredentialsInternal().addAll(credentials);
        }
    }

    private synchronized Credentials getCredentialsInternal() {
        final Credentials credentials;
        final Set<Credentials> credentialsSet = subject.getPrivateCredentials(Credentials.class);
        if (!credentialsSet.isEmpty()) {
            credentials = credentialsSet.iterator().next();
        } else {
            //            credentials = new Credentials();
            //            subject.getPrivateCredentials().add(credentials);
        }
        //        return credentials;
        return null;
    }

    /**
     * Get the group names for this user.
     *
     * @return the list of users with the primary group first. If the command fails, it returns an empty list.
     */
    public synchronized String[] getGroupNames() {
        ensureInitialized();
        try {
            Set<String> result = new LinkedHashSet<String>(groups.getGroups(getShortUserName()));
            return result.toArray(new String[result.size()]);
        } catch (IOException ie) {
            LOG.warn("No groups available for user " + getShortUserName());
            return new String[0];
        }
    }

    /**
     * Return the username.
     */
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(getUserName());
        sb.append(" (auth:" + getAuthenticationMethod() + ")");
        if (getRealUser() != null) {
            sb.append(" via ").append(getRealUser().toString());
        }
        return sb.toString();
    }

    /**
     * Sets the authentication method in the subject
     *
     * @param authMethod
     */
    public synchronized void setAuthenticationMethod(AuthenticationMethod authMethod) {
        user.setAuthenticationMethod(authMethod);
    }

    /**
     * Sets the authentication method in the subject
     *
     * @param authMethod
     */
    //    public void setAuthenticationMethod(AuthMethod authMethod) {
    //        user.setAuthenticationMethod(AuthenticationMethod.valueOf(authMethod));
    //    }

    /**
     * Get the authentication method from the subject
     *
     * @return AuthenticationMethod in the subject, null if not present.
     */
    public synchronized AuthenticationMethod getAuthenticationMethod() {
        return user.getAuthenticationMethod();
    }

    /**
     * Get the authentication method from the real user's subject.  If there is no real user, return the given user's
     * authentication method.
     *
     * @return AuthenticationMethod in the subject, null if not present.
     */
    public synchronized AuthenticationMethod getRealAuthenticationMethod() {
        UserGroupInformation ugi = getRealUser();
        if (ugi == null) {
            ugi = this;
        }
        return ugi.getAuthenticationMethod();
    }

    /**
     * Returns the authentication method of a ugi. If the authentication method is PROXY, returns the authentication
     * method of the real user.
     *
     * @param ugi
     *
     * @return AuthenticationMethod
     */
    public static AuthenticationMethod getRealAuthenticationMethod(UserGroupInformation ugi) {
        AuthenticationMethod authMethod = ugi.getAuthenticationMethod();
        if (authMethod == AuthenticationMethod.PROXY) {
            authMethod = ugi.getRealUser().getAuthenticationMethod();
        }
        return authMethod;
    }

    /**
     * Compare the subjects to see if they are equal to each other.
     */
    @Override
    public boolean equals(Object o) {
        if (o == this) {
            return true;
        } else if (o == null || getClass() != o.getClass()) {
            return false;
        } else {
            return subject == ((UserGroupInformation) o).subject;
        }
    }

    /**
     * Return the hash of the subject.
     */
    @Override
    public int hashCode() {
        return System.identityHashCode(subject);
    }

    /**
     * Get the underlying subject from this ugi.
     *
     * @return the subject that represents this user.
     */
    protected Subject getSubject() {
        return subject;
    }

    /**
     * Run the given action as the user.
     *
     * @param <T>    the return type of the run method
     * @param action the method to execute
     *
     * @return the value from the run method
     */

    public <T> T doAs(PrivilegedAction<T> action) {
        logPrivilegedAction(subject, action);
        return Subject.doAs(subject, action);
    }

    /**
     * Run the given action as the user, potentially throwing an exception.
     *
     * @param <T>    the return type of the run method
     * @param action the method to execute
     *
     * @return the value from the run method
     *
     * @throws IOException                  if the action throws an IOException
     * @throws Error                        if the action throws an Error
     * @throws RuntimeException             if the action throws a RuntimeException
     * @throws InterruptedException         if the action throws an InterruptedException
     * @throws UndeclaredThrowableException if the action throws something else
     */

    public <T> T doAs(PrivilegedExceptionAction<T> action) throws IOException, InterruptedException {
        try {
            logPrivilegedAction(subject, action);
            return Subject.doAs(subject, action);
        } catch (PrivilegedActionException pae) {
            Throwable cause = pae.getCause();
            if (LOG.isDebugEnabled()) {
                LOG.debug("PrivilegedActionException as:" + this + " cause:" + cause);
            }
            if (cause instanceof IOException) {
                throw (IOException) cause;
            } else if (cause instanceof Error) {
                throw (Error) cause;
            } else if (cause instanceof RuntimeException) {
                throw (RuntimeException) cause;
            } else if (cause instanceof InterruptedException) {
                throw (InterruptedException) cause;
            } else {
                throw new UndeclaredThrowableException(cause);
            }
        }
    }

    private void logPrivilegedAction(Subject subject, Object action) {
        if (LOG.isDebugEnabled()) {
            // would be nice if action included a descriptive toString()
            String where = new Throwable().getStackTrace()[2].toString();
            LOG.debug("PrivilegedAction as:" + this + " from:" + where);
        }
    }

    private void print() throws IOException {
        System.out.println("User: " + getUserName());
        System.out.print("Group Ids: ");
        System.out.println();
        String[] groups = getGroupNames();
        System.out.print("Groups: ");
        for (int i = 0; i < groups.length; i++) {
            System.out.print(groups[i] + " ");
        }
        System.out.println();
    }

    /**
     * A test method to print out the current user's UGI.
     *
     * @param args if there are two arguments, read the user from the keytab and print it out.
     *
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        System.out.println("Getting UGI for current user");
        UserGroupInformation ugi = getCurrentUser();
        ugi.print();
        System.out.println("UGI: " + ugi);
        System.out.println("Auth method " + ugi.user.getAuthenticationMethod());
        System.out.println("Keytab " + ugi.isKeytab);
        System.out.println("============================================================");

        if (args.length == 2) {
            System.out.println("Getting UGI from keytab....");
            loginUserFromKeytab(args[0], args[1]);
            getCurrentUser().print();
            System.out.println("Keytab: " + ugi);
            System.out.println("Auth method " + loginUser.user.getAuthenticationMethod());
            System.out.println("Keytab " + loginUser.isKeytab);
        }
    }

}