org.apache.hadoop.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
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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 org.apache.hadoop.security;

import static org.apache.hadoop.fs.CommonConfigurationKeys.HADOOP_USER_GROUP_METRICS_PERCENTILES_INTERVALS;
import static org.apache.hadoop.fs.CommonConfigurationKeysPublic.HADOOP_KERBEROS_MIN_SECONDS_BEFORE_RELOGIN;
import static org.apache.hadoop.fs.CommonConfigurationKeysPublic.HADOOP_KERBEROS_MIN_SECONDS_BEFORE_RELOGIN_DEFAULT;
import static org.apache.hadoop.fs.CommonConfigurationKeysPublic.HADOOP_TOKEN_FILES;
import static org.apache.hadoop.security.UGIExceptionMessages.*;
import static org.apache.hadoop.util.PlatformName.IBM_JAVA;

import com.google.common.annotations.VisibleForTesting;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.reflect.UndeclaredThrowableException;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.Principal;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

import javax.security.auth.DestroyFailedException;
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.login.AppConfigurationEntry;
import javax.security.auth.login.AppConfigurationEntry.LoginModuleControlFlag;
import javax.security.auth.login.Configuration.Parameters;
import javax.security.auth.login.LoginContext;
import javax.security.auth.login.LoginException;
import javax.security.auth.spi.LoginModule;

import org.apache.hadoop.io.retry.RetryPolicies;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.retry.RetryPolicy;
import org.apache.hadoop.metrics2.annotation.Metric;
import org.apache.hadoop.metrics2.annotation.Metrics;
import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
import org.apache.hadoop.metrics2.lib.MetricsRegistry;
import org.apache.hadoop.metrics2.lib.MutableGaugeInt;
import org.apache.hadoop.metrics2.lib.MutableGaugeLong;
import org.apache.hadoop.metrics2.lib.MutableQuantiles;
import org.apache.hadoop.metrics2.lib.MutableRate;
import org.apache.hadoop.security.SaslRpcServer.AuthMethod;
import org.apache.hadoop.security.authentication.util.KerberosUtil;
import org.apache.hadoop.security.token.Token;
import org.apache.hadoop.security.token.TokenIdentifier;
import org.apache.hadoop.util.Shell;
import org.apache.hadoop.util.StringUtils;
import org.apache.hadoop.util.Time;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 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.
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public class UserGroupInformation {
    @VisibleForTesting
    static final Logger LOG = LoggerFactory.getLogger(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
    public 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;
        @Metric("Renewal failures since startup")
        private MutableGaugeLong renewalFailuresTotal;
        @Metric("Renewal failures since last successful login")
        private MutableGaugeInt renewalFailures;

        static UgiMetrics create() {
            return DefaultMetricsSystem.instance().register(new UgiMetrics());
        }

        static void reattach() {
            metrics = UgiMetrics.create();
        }

        void addGetGroups(long latency) {
            getGroups.add(latency);
            if (getGroupsQuantiles != null) {
                for (MutableQuantiles q : getGroupsQuantiles) {
                    q.add(latency);
                }
            }
        }

        MutableGaugeInt getRenewalFailures() {
            return renewalFailures;
        }
    }

    /**
     * A login module that looks at the Kerberos, Unix, or Windows principal and
     * adds the corresponding UserName.
     */
    @InterfaceAudience.Private
    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 = getCanonicalUser(KerberosPrincipal.class);
            if (user != null) {
                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 {
                    // LoginContext will be attached later unless it's an external
                    // subject.
                    AuthenticationMethod authMethod = (user instanceof KerberosPrincipal)
                            ? AuthenticationMethod.KERBEROS
                            : AuthenticationMethod.SIMPLE;
                    userEntry = new User(user.getName(), authMethod, null);
                } 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;
        }
    }

    /**
     * Reattach the class's metrics to a new metric system.
     */
    public static void reattachMetrics() {
        UgiMetrics.reattach();
    }

    /** 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;
    /** Min time (in seconds) before relogin for Kerberos */
    private static long kerberosMinSecondsBeforeRelogin;
    /** The configuration to use */

    private static Configuration conf;

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

    public static boolean isInitialized() {
        return conf != null;
    }

    /** 
     * 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 (!isInitialized()) {
            synchronized (UserGroupInformation.class) {
                if (!isInitialized()) { // 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);
            }
        }
        try {
            kerberosMinSecondsBeforeRelogin = 1000L * conf.getLong(HADOOP_KERBEROS_MIN_SECONDS_BEFORE_RELOGIN,
                    HADOOP_KERBEROS_MIN_SECONDS_BEFORE_RELOGIN_DEFAULT);
        } catch (NumberFormatException nfe) {
            throw new IllegalArgumentException(
                    "Invalid attribute value for " + HADOOP_KERBEROS_MIN_SECONDS_BEFORE_RELOGIN + " of "
                            + conf.get(HADOOP_KERBEROS_MIN_SECONDS_BEFORE_RELOGIN));
        }
        // 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
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public static void setConfiguration(Configuration conf) {
        initialize(conf, true);
    }

    @InterfaceAudience.Private
    @VisibleForTesting
    public static void reset() {
        authenticationMethod = null;
        conf = null;
        groups = null;
        kerberosMinSecondsBeforeRelogin = 0;
        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);
    }

    @InterfaceAudience.Private
    @InterfaceStability.Evolving
    private static boolean isAuthenticationMethodEnabled(AuthenticationMethod method) {
        ensureInitialized();
        return (authenticationMethod == method);
    }

    /**
     * Information about the logged in user.
     */
    private static final AtomicReference<UserGroupInformation> loginUserRef = new AtomicReference<>();

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

    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")
            || System.getProperty("os.arch").contains("s390x");
    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();
        }
    }

    private static HadoopLoginContext newLoginContext(String appName, Subject subject,
            HadoopConfiguration 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 HadoopLoginContext(appName, subject, loginConf);
        } finally {
            t.setContextClassLoader(oldCCL);
        }
    }

    // return the LoginContext only if it's managed by the ugi.  externally
    // managed login contexts will be ignored.
    private HadoopLoginContext getLogin() {
        LoginContext login = user.getLogin();
        return (login instanceof HadoopLoginContext) ? (HadoopLoginContext) login : null;
    }

    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.
     *
     * The creator of subject is responsible for renewing credentials.
     * @param subject the user's subject
     */
    UserGroupInformation(Subject subject) {
        this.subject = subject;
        // do not access ANY private credentials since they are mutable
        // during a relogin.  no principal locking necessary since
        // relogin/logout does not remove User principal.
        this.user = subject.getPrincipals(User.class).iterator().next();
        if (user == null || user.getName() == null) {
            throw new IllegalStateException("Subject does not contain a valid User");
        }
    }

    /**
     * checks if logged in using kerberos
     * @return true if the subject logged via keytab or has a Kerberos TGT
     */
    public boolean hasKerberosCredentials() {
        return user.getAuthenticationMethod() == AuthenticationMethod.KERBEROS;
    }

    /**
     * Return the current user, including any doAs in the current stack.
     * @return the current user
     * @throws IOException if login fails
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public 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
     * @param ticketCache     the path to the ticket cache file
     *
     * @throws IOException        if the kerberos login fails
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public static UserGroupInformation getUGIFromTicketCache(String ticketCache, String user) throws IOException {
        if (!isAuthenticationMethodEnabled(AuthenticationMethod.KERBEROS)) {
            return getBestUGI(null, user);
        }
        LoginParams params = new LoginParams();
        params.put(LoginParam.PRINCIPAL, user);
        params.put(LoginParam.CCACHE, ticketCache);
        return doSubjectLogin(null, params);
    }

    /**
     * Create a UserGroupInformation from a Subject with Kerberos principal.
     *
     * @param subject             The KerberosPrincipal to use in UGI.
     *                            The creator of subject is responsible for
     *                            renewing credentials.
     *
     * @throws IOException
     * @throws KerberosAuthException if the kerberos login fails
     */
    public static UserGroupInformation getUGIFromSubject(Subject subject) throws IOException {
        if (subject == null) {
            throw new KerberosAuthException(SUBJECT_MUST_NOT_BE_NULL);
        }

        if (subject.getPrincipals(KerberosPrincipal.class).isEmpty()) {
            throw new KerberosAuthException(SUBJECT_MUST_CONTAIN_PRINCIPAL);
        }

        // null params indicate external subject login.  no login context will
        // be attached.
        return doSubjectLogin(subject, null);
    }

    /**
     * Get the currently logged in user.  If no explicit login has occurred,
     * the user will automatically be logged in with either kerberos credentials
     * if available, or as the local OS user, based on security settings.
     * @return the logged in user
     * @throws IOException if login fails
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public static UserGroupInformation getLoginUser() throws IOException {
        UserGroupInformation loginUser = loginUserRef.get();
        // a potential race condition exists only for the initial creation of
        // the login user.  there's no need to penalize all subsequent calls
        // with sychronization overhead so optimistically create a login user
        // and discard if we lose the race.
        if (loginUser == null) {
            UserGroupInformation newLoginUser = createLoginUser(null);
            do {
                // it's extremely unlikely that the login user will be non-null
                // (lost CAS race), but be nulled before the subsequent get, but loop
                // for correctness.
                if (loginUserRef.compareAndSet(null, newLoginUser)) {
                    loginUser = newLoginUser;
                    // only spawn renewal if this login user is the winner.
                    loginUser.spawnAutoRenewalThreadForUserCreds(false);
                } else {
                    loginUser = loginUserRef.get();
                }
            } while (loginUser == 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
     * @param subject the subject to use when logging in a user, or null to
     * create a new subject.
     *
     * If subject is not null, the creator of subject is responsible for renewing
     * credentials.
     *
     * @throws IOException if login fails
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public static void loginUserFromSubject(Subject subject) throws IOException {
        setLoginUser(createLoginUser(subject));
    }

    private static UserGroupInformation createLoginUser(Subject subject) throws IOException {
        UserGroupInformation realUser = doSubjectLogin(subject, null);
        UserGroupInformation loginUser = null;
        try {
            // 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 tokenFileLocation = System.getProperty(HADOOP_TOKEN_FILES);
            if (tokenFileLocation == null) {
                tokenFileLocation = conf.get(HADOOP_TOKEN_FILES);
            }
            if (tokenFileLocation != null) {
                for (String tokenFileName : StringUtils.getTrimmedStrings(tokenFileLocation)) {
                    if (tokenFileName.length() > 0) {
                        File tokenFile = new File(tokenFileName);
                        if (tokenFile.exists() && tokenFile.isFile()) {
                            Credentials cred = Credentials.readTokenStorageFile(tokenFile, conf);
                            loginUser.addCredentials(cred);
                        } else {
                            LOG.info("tokenFile(" + tokenFileName + ") does not exist");
                        }
                    }
                }
            }

            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).
                File source = new File(fileLocation);
                LOG.debug("Reading credentials from location set in {}: {}", HADOOP_TOKEN_FILE_LOCATION,
                        source.getCanonicalPath());
                if (!source.isFile()) {
                    throw new FileNotFoundException("Source file " + source.getCanonicalPath() + " from "
                            + HADOOP_TOKEN_FILE_LOCATION + " not found");
                }
                Credentials cred = Credentials.readTokenStorageFile(source, conf);
                LOG.debug("Loaded {} tokens", cred.numberOfTokens());
                loginUser.addCredentials(cred);
            }
        } catch (IOException ioe) {
            LOG.debug("failure to load login credentials", ioe);
            throw ioe;
        }
        if (LOG.isDebugEnabled()) {
            LOG.debug("UGI loginUser:" + loginUser);
        }
        return loginUser;
    }

    @InterfaceAudience.Private
    @InterfaceStability.Unstable
    @VisibleForTesting
    public static void setLoginUser(UserGroupInformation ugi) {
        // if this is to become stable, should probably logout the currently
        // logged in ugi if it's different
        loginUserRef.set(ugi);
    }

    private String getKeytab() {
        HadoopLoginContext login = getLogin();
        return (login != null) ? login.getConfiguration().getParameters().get(LoginParam.KEYTAB) : null;
    }

    /**
     * Is the ugi managed by the UGI or an external subject?
     * @return true if managed by UGI.
     */
    private boolean isHadoopLogin() {
        // checks if the private hadoop login context is managing the ugi.
        return getLogin() != null;
    }

    /**
     * Is this user logged in from a keytab file managed by the UGI?
     * @return true if the credentials are from a keytab file.
     */
    public boolean isFromKeytab() {
        // can't simply check if keytab is present since a relogin failure will
        // have removed the keytab from priv creds.  instead, check login params.
        return hasKerberosCredentials() && isHadoopLogin() && getKeytab() != null;
    }

    /**
     *  Is this user logged in from a ticket (but no keytab) managed by the UGI?
     * @return true if the credentials are from a ticket cache.
     */
    private boolean isFromTicket() {
        return hasKerberosCredentials() && isHadoopLogin() && getKeytab() == null;
    }

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

    @InterfaceAudience.Private
    @InterfaceStability.Unstable
    public boolean shouldRelogin() {
        return hasKerberosCredentials() && isHadoopLogin();
    }

    @InterfaceAudience.Private
    @InterfaceStability.Unstable
    @VisibleForTesting
    /**
     * Spawn a thread to do periodic renewals of kerberos credentials from
     * a ticket cache.  NEVER directly call this method.
     * @param force - used by tests to forcibly spawn thread
     */
    void spawnAutoRenewalThreadForUserCreds(boolean force) {
        if (!force && (!shouldRelogin() || isFromKeytab())) {
            return;
        }

        //spawn thread only if we have kerb credentials
        KerberosTicket tgt = getTGT();
        if (tgt == null) {
            return;
        }
        String cmd = conf.get("hadoop.kerberos.kinit.command", "kinit");
        long nextRefresh = getRefreshTime(tgt);
        Thread t = new Thread(new AutoRenewalForUserCredsRunnable(tgt, cmd, nextRefresh));
        t.setDaemon(true);
        t.setName("TGT Renewer for " + getUserName());
        t.start();
    }

    @VisibleForTesting
    class AutoRenewalForUserCredsRunnable implements Runnable {
        private KerberosTicket tgt;
        private RetryPolicy rp;
        private String kinitCmd;
        private long nextRefresh;
        private boolean runRenewalLoop = true;

        AutoRenewalForUserCredsRunnable(KerberosTicket tgt, String kinitCmd, long nextRefresh) {
            this.tgt = tgt;
            this.kinitCmd = kinitCmd;
            this.nextRefresh = nextRefresh;
            this.rp = null;
        }

        public void setRunRenewalLoop(boolean runRenewalLoop) {
            this.runRenewalLoop = runRenewalLoop;
        }

        @Override
        public void run() {
            do {
                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);
                    }
                    String output = Shell.execCommand(kinitCmd, "-R");
                    if (LOG.isDebugEnabled()) {
                        LOG.debug("Renewed ticket. kinit output: {}", output);
                    }
                    reloginFromTicketCache();
                    tgt = getTGT();
                    if (tgt == null) {
                        LOG.warn("No TGT after renewal. Aborting renew thread for " + getUserName());
                        return;
                    }
                    nextRefresh = Math.max(getRefreshTime(tgt), now + kerberosMinSecondsBeforeRelogin);
                    metrics.renewalFailures.set(0);
                    rp = null;
                } catch (InterruptedException ie) {
                    LOG.warn("Terminating renewal thread");
                    return;
                } catch (IOException ie) {
                    metrics.renewalFailuresTotal.incr();
                    final long now = Time.now();

                    if (tgt.isDestroyed()) {
                        LOG.error("TGT is destroyed. Aborting renew thread for {}.", getUserName());
                        return;
                    }

                    long tgtEndTime;
                    // As described in HADOOP-15593 we need to handle the case when
                    // tgt.getEndTime() throws NPE because of JDK issue JDK-8147772
                    // NPE is only possible if this issue is not fixed in the JDK
                    // currently used
                    try {
                        tgtEndTime = tgt.getEndTime().getTime();
                    } catch (NullPointerException npe) {
                        LOG.error("NPE thrown while getting KerberosTicket endTime. "
                                + "Aborting renew thread for {}.", getUserName());
                        return;
                    }

                    LOG.warn(
                            "Exception encountered while running the renewal "
                                    + "command for {}. (TGT end time:{}, renewalFailures: {},"
                                    + "renewalFailuresTotal: {})",
                            getUserName(), tgtEndTime, metrics.renewalFailures.value(),
                            metrics.renewalFailuresTotal.value(), ie);
                    if (rp == null) {
                        // Use a dummy maxRetries to create the policy. The policy will
                        // only be used to get next retry time with exponential back-off.
                        // The final retry time will be later limited within the
                        // tgt endTime in getNextTgtRenewalTime.
                        rp = RetryPolicies.exponentialBackoffRetry(Long.SIZE - 2, kerberosMinSecondsBeforeRelogin,
                                TimeUnit.MILLISECONDS);
                    }
                    try {
                        nextRefresh = getNextTgtRenewalTime(tgtEndTime, now, rp);
                    } catch (Exception e) {
                        LOG.error("Exception when calculating next tgt renewal time", e);
                        return;
                    }
                    metrics.renewalFailures.incr();
                    // retry until close enough to tgt endTime.
                    if (now > nextRefresh) {
                        LOG.error("TGT is expired. Aborting renew thread for {}.", getUserName());
                        return;
                    }
                }
            } while (runRenewalLoop);
        }
    }

    /**
     * Get time for next login retry. This will allow the thread to retry with
     * exponential back-off, until tgt endtime.
     * Last retry is {@link #kerberosMinSecondsBeforeRelogin} before endtime.
     *
     * @param tgtEndTime EndTime of the tgt.
     * @param now Current time.
     * @param rp The retry policy.
     * @return Time for next login retry.
     */
    @VisibleForTesting
    static long getNextTgtRenewalTime(final long tgtEndTime, final long now, final RetryPolicy rp)
            throws Exception {
        final long lastRetryTime = tgtEndTime - kerberosMinSecondsBeforeRelogin;
        final RetryPolicy.RetryAction ra = rp.shouldRetry(null, metrics.renewalFailures.value(), 0, false);
        return Math.min(lastRetryTime, now + ra.delayMillis);
    }

    /**
     * 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
     * @throws KerberosAuthException if it's a kerberos login exception.
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public static void loginUserFromKeytab(String user, String path) throws IOException {
        if (!isSecurityEnabled())
            return;

        setLoginUser(loginUserFromKeytabAndReturnUGI(user, path));
        LOG.info("Login successful for user " + user + " using keytab file " + path);
    }

    /**
     * Log the current user out who previously logged in using keytab.
     * This method assumes that the user logged in by calling
     * {@link #loginUserFromKeytab(String, String)}.
     *
     * @throws IOException
     * @throws KerberosAuthException if a failure occurred in logout,
     * or if the user did not log in by invoking loginUserFromKeyTab() before.
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public void logoutUserFromKeytab() throws IOException {
        if (!hasKerberosCredentials()) {
            return;
        }
        HadoopLoginContext login = getLogin();
        String keytabFile = getKeytab();
        if (login == null || keytabFile == null) {
            throw new KerberosAuthException(MUST_FIRST_LOGIN_FROM_KEYTAB);
        }

        try {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Initiating logout for " + getUserName());
            }
            // hadoop login context internally locks credentials.
            login.logout();
        } catch (LoginException le) {
            KerberosAuthException kae = new KerberosAuthException(LOGOUT_FAILURE, le);
            kae.setUser(user.toString());
            kae.setKeytabFile(keytabFile);
            throw kae;
        }

        LOG.info("Logout successful for user " + getUserName() + " using keytab file " + keytabFile);
    }

    /**
     * Re-login a user from keytab if TGT is expired or is close to expiry.
     * 
     * @throws IOException
     * @throws KerberosAuthException if it's a kerberos login exception.
     */
    public void checkTGTAndReloginFromKeytab() throws IOException {
        reloginFromKeytab(true);
    }

    // if the first kerberos ticket is not TGT, then remove and destroy it since
    // the kerberos library of jdk always use the first kerberos ticket as TGT.
    // See HADOOP-13433 for more details.
    @VisibleForTesting
    void fixKerberosTicketOrder() {
        Set<Object> creds = getSubject().getPrivateCredentials();
        synchronized (creds) {
            for (Iterator<Object> iter = creds.iterator(); iter.hasNext();) {
                Object cred = iter.next();
                if (cred instanceof KerberosTicket) {
                    KerberosTicket ticket = (KerberosTicket) cred;
                    if (ticket.isDestroyed() || ticket.getServer() == null) {
                        LOG.warn("Ticket is already destroyed, remove it.");
                        iter.remove();
                    } else if (!ticket.getServer().getName().startsWith("krbtgt")) {
                        LOG.warn(
                                "The first kerberos ticket is not TGT"
                                        + "(the server principal is {}), remove and destroy it.",
                                ticket.getServer());
                        iter.remove();
                        try {
                            ticket.destroy();
                        } catch (DestroyFailedException e) {
                            LOG.warn("destroy ticket failed", e);
                        }
                    } else {
                        return;
                    }
                }
            }
        }
        LOG.warn("Warning, no kerberos ticket found while attempting to renew ticket");
    }

    /**
     * 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
     * @throws KerberosAuthException on a failure
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public void reloginFromKeytab() throws IOException {
        reloginFromKeytab(false);
    }

    private void reloginFromKeytab(boolean checkTGT) throws IOException {
        if (!shouldRelogin() || !isFromKeytab()) {
            return;
        }
        HadoopLoginContext login = getLogin();
        if (login == null) {
            throw new KerberosAuthException(MUST_FIRST_LOGIN_FROM_KEYTAB);
        }
        if (checkTGT) {
            KerberosTicket tgt = getTGT();
            if (tgt != null && !shouldRenewImmediatelyForTests && Time.now() < getRefreshTime(tgt)) {
                return;
            }
        }
        relogin(login);
    }

    /**
     * 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
     * @throws KerberosAuthException on a failure
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public void reloginFromTicketCache() throws IOException {
        if (!shouldRelogin() || !isFromTicket()) {
            return;
        }
        HadoopLoginContext login = getLogin();
        if (login == null) {
            throw new KerberosAuthException(MUST_FIRST_LOGIN);
        }
        relogin(login);
    }

    private void relogin(HadoopLoginContext login) throws IOException {
        // ensure the relogin is atomic to avoid leaving credentials in an
        // inconsistent state.  prevents other ugi instances, SASL, and SPNEGO
        // from accessing or altering credentials during the relogin.
        synchronized (login.getSubjectLock()) {
            // another racing thread may have beat us to the relogin.
            if (login == getLogin()) {
                unprotectedRelogin(login);
            }
        }
    }

    private void unprotectedRelogin(HadoopLoginContext login) throws IOException {
        assert Thread.holdsLock(login.getSubjectLock());
        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(login.getAppName(), login.getSubject(), login.getConfiguration());
            if (LOG.isDebugEnabled()) {
                LOG.debug("Initiating re-login for " + getUserName());
            }
            login.login();
            // this should be unnecessary.  originally added due to improper locking
            // of the subject during relogin.
            fixKerberosTicketOrder();
            setLogin(login);
        } catch (LoginException le) {
            KerberosAuthException kae = new KerberosAuthException(LOGIN_FAILURE, le);
            kae.setUser(getUserName());
            throw kae;
        }
    }

    /**
     * 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 static UserGroupInformation loginUserFromKeytabAndReturnUGI(String user, String path)
            throws IOException {
        if (!isSecurityEnabled())
            return UserGroupInformation.getCurrentUser();

        LoginParams params = new LoginParams();
        params.put(LoginParam.PRINCIPAL, user);
        params.put(LoginParam.KEYTAB, path);
        return doSubjectLogin(null, params);
    }

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

    /**
     * Did the login happen via keytab
     * @return true or false
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public static boolean isLoginKeytabBased() throws IOException {
        return getLoginUser().isFromKeytab();
    }

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

    /**
     * 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.
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public static UserGroupInformation createRemoteUser(String user) {
        return createRemoteUser(user, AuthMethod.SIMPLE);
    }

    /**
     * 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.
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    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
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    public 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.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
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    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, AuthenticationMethod.PROXY, null));
        principals.add(new RealUser(realUser));
        return new UserGroupInformation(subject);
    }

    /**
     * get RealUser (vs. EffectiveUser)
     * @return realUser running over proxy user
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    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 org.apache.hadoop.conf.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
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    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() {
        return user.getShortName();
    }

    public String getPrimaryGroupName() throws IOException {
        List<String> groups = getGroups();
        if (groups.isEmpty()) {
            throw new IOException("There is no primary group for UGI " + this);
        }
        return groups.get(0);
    }

    /**
     * Get the user's full principal name.
     * @return the user's full principal name.
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    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;
    }

    /**
     * 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()));
        }
    }

    /**
     * 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().isPrivate()) {
                    iter.remove();
                }
            }
            return creds;
        }
    }

    /**
     * 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;
    }

    /**
     * Get the group names for this user. {@link #getGroups()} is less
     * expensive alternative when checking for a contained element.
     * @return the list of users with the primary group first. If the command
     *    fails, it returns an empty list.
     */
    public String[] getGroupNames() {
        List<String> groups = getGroups();
        return groups.toArray(new String[groups.size()]);
    }

    /**
     * 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 List<String> getGroups() {
        ensureInitialized();
        try {
            return groups.getGroups(getShortUserName());
        } catch (IOException ie) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Failed to get groups for user " + getShortUserName() + " by " + ie);
                LOG.trace("TRACE", ie);
            }
            return Collections.emptyList();
        }
    }

    /**
     * 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
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    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
     */
    @InterfaceAudience.Public
    @InterfaceStability.Evolving
    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 == null) {
                throw new RuntimeException(
                        "PrivilegedActionException with no " + "underlying cause. UGI [" + this + "]" + ": " + pae,
                        pae);
            } else 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);
        }
    }

    /**
     * Log current UGI and token information into specified log.
     * @param ugi - UGI
     * @throws IOException
     */
    @InterfaceAudience.LimitedPrivate({ "HDFS", "KMS" })
    @InterfaceStability.Unstable
    public static void logUserInfo(Logger log, String caption, UserGroupInformation ugi) throws IOException {
        if (log.isDebugEnabled()) {
            log.debug(caption + " UGI: " + ugi);
            for (Token<?> token : ugi.getTokens()) {
                log.debug("+token:" + token);
            }
        }
    }

    /**
     * Log all (current, real, login) UGI and token info into specified log.
     * @param ugi - UGI
     * @throws IOException
     */
    @InterfaceAudience.LimitedPrivate({ "HDFS", "KMS" })
    @InterfaceStability.Unstable
    public static void logAllUserInfo(Logger log, UserGroupInformation ugi) throws IOException {
        if (log.isDebugEnabled()) {
            logUserInfo(log, "Current", ugi.getCurrentUser());
            if (ugi.getRealUser() != null) {
                logUserInfo(log, "Real", ugi.getRealUser());
            }
            logUserInfo(log, "Login", ugi.getLoginUser());
        }
    }

    /**
     * Log all (current, real, login) UGI and token info into UGI debug log.
     * @param ugi - UGI
     * @throws IOException
     */
    public static void logAllUserInfo(UserGroupInformation ugi) throws IOException {
        logAllUserInfo(LOG, ugi);
    }

    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();
    }

    /**
     * Login a subject with the given parameters.  If the subject is null,
     * the login context used to create the subject will be attached.
     * @param subject to login, null for new subject.
     * @param params for login, null for externally managed ugi.
     * @return UserGroupInformation for subject
     * @throws IOException
     */
    private static UserGroupInformation doSubjectLogin(Subject subject, LoginParams params) throws IOException {
        ensureInitialized();
        // initial default login.
        if (subject == null && params == null) {
            params = LoginParams.getDefaults();
        }
        HadoopConfiguration loginConf = new HadoopConfiguration(params);
        try {
            HadoopLoginContext login = newLoginContext(authenticationMethod.getLoginAppName(), subject, loginConf);
            login.login();
            UserGroupInformation ugi = new UserGroupInformation(login.getSubject());
            // attach login context for relogin unless this was a pre-existing
            // subject.
            if (subject == null) {
                params.put(LoginParam.PRINCIPAL, ugi.getUserName());
                ugi.setLogin(login);
            }
            return ugi;
        } catch (LoginException le) {
            KerberosAuthException kae = new KerberosAuthException(FAILURE_TO_LOGIN, le);
            if (params != null) {
                kae.setPrincipal(params.get(LoginParam.PRINCIPAL));
                kae.setKeytabFile(params.get(LoginParam.KEYTAB));
                kae.setTicketCacheFile(params.get(LoginParam.CCACHE));
            }
            throw kae;
        }
    }

    // parameters associated with kerberos logins.  may be extended to support
    // additional authentication methods.
    enum LoginParam {
        PRINCIPAL, KEYTAB, CCACHE,
    }

    // explicitly private to prevent external tampering.
    private static class LoginParams extends EnumMap<LoginParam, String> implements Parameters {
        LoginParams() {
            super(LoginParam.class);
        }

        // do not add null values, nor allow existing values to be overriden.
        @Override
        public String put(LoginParam param, String val) {
            boolean add = val != null && !containsKey(param);
            return add ? super.put(param, val) : null;
        }

        static LoginParams getDefaults() {
            LoginParams params = new LoginParams();
            params.put(LoginParam.PRINCIPAL, System.getenv("KRB5PRINCIPAL"));
            params.put(LoginParam.KEYTAB, System.getenv("KRB5KEYTAB"));
            params.put(LoginParam.CCACHE, System.getenv("KRB5CCNAME"));
            return params;
        }
    }

    // wrapper to allow access to fields necessary to recreate the same login
    // context for relogin.  explicitly private to prevent external tampering.
    private static class HadoopLoginContext extends LoginContext {
        private final String appName;
        private final HadoopConfiguration conf;
        private AtomicBoolean isLoggedIn = new AtomicBoolean();

        HadoopLoginContext(String appName, Subject subject, HadoopConfiguration conf) throws LoginException {
            super(appName, subject, null, conf);
            this.appName = appName;
            this.conf = conf;
        }

        String getAppName() {
            return appName;
        }

        HadoopConfiguration getConfiguration() {
            return conf;
        }

        // the locking model for logins cannot rely on ugi instance synchronization
        // since a subject will be referenced by multiple ugi instances.
        Object getSubjectLock() {
            Subject subject = getSubject();
            // if subject is null, the login context will create the subject
            // so just lock on this context.
            return (subject == null) ? this : subject.getPrivateCredentials();
        }

        @Override
        public void login() throws LoginException {
            synchronized (getSubjectLock()) {
                MutableRate metric = metrics.loginFailure;
                long start = Time.monotonicNow();
                try {
                    super.login();
                    isLoggedIn.set(true);
                    metric = metrics.loginSuccess;
                } finally {
                    metric.add(Time.monotonicNow() - start);
                }
            }
        }

        @Override
        public void logout() throws LoginException {
            synchronized (getSubjectLock()) {
                if (isLoggedIn.compareAndSet(true, false)) {
                    super.logout();
                }
            }
        }
    }

    /**
     * A JAAS configuration that defines the login modules that we want
     * to use for login.
     */
    @InterfaceAudience.Private
    @InterfaceStability.Unstable
    private static class HadoopConfiguration extends javax.security.auth.login.Configuration {
        static final String KRB5_LOGIN_MODULE = KerberosUtil.getKrb5LoginModuleName();
        static final String SIMPLE_CONFIG_NAME = "hadoop-simple";
        static final String KERBEROS_CONFIG_NAME = "hadoop-kerberos";

        private static final Map<String, String> BASIC_JAAS_OPTIONS = new HashMap<String, String>();
        static {
            if ("true".equalsIgnoreCase(System.getenv("HADOOP_JAAS_DEBUG"))) {
                BASIC_JAAS_OPTIONS.put("debug", "true");
            }
        }

        static final AppConfigurationEntry OS_SPECIFIC_LOGIN = new AppConfigurationEntry(OS_LOGIN_MODULE_NAME,
                LoginModuleControlFlag.REQUIRED, BASIC_JAAS_OPTIONS);

        static final AppConfigurationEntry HADOOP_LOGIN = new AppConfigurationEntry(
                HadoopLoginModule.class.getName(), LoginModuleControlFlag.REQUIRED, BASIC_JAAS_OPTIONS);

        private final LoginParams params;

        HadoopConfiguration(LoginParams params) {
            this.params = params;
        }

        @Override
        public LoginParams getParameters() {
            return params;
        }

        @Override
        public AppConfigurationEntry[] getAppConfigurationEntry(String appName) {
            ArrayList<AppConfigurationEntry> entries = new ArrayList<>();
            // login of external subject passes no params.  technically only
            // existing credentials should be used but other components expect
            // the login to succeed with local user fallback if no principal.
            if (params == null || appName.equals(SIMPLE_CONFIG_NAME)) {
                entries.add(OS_SPECIFIC_LOGIN);
            } else if (appName.equals(KERBEROS_CONFIG_NAME)) {
                // existing semantics are the initial default login allows local user
                // fallback. this is not allowed when a principal explicitly
                // specified or during a relogin.
                if (!params.containsKey(LoginParam.PRINCIPAL)) {
                    entries.add(OS_SPECIFIC_LOGIN);
                }
                entries.add(getKerberosEntry());
            }
            entries.add(HADOOP_LOGIN);
            return entries.toArray(new AppConfigurationEntry[0]);
        }

        private AppConfigurationEntry getKerberosEntry() {
            final Map<String, String> options = new HashMap<>(BASIC_JAAS_OPTIONS);
            LoginModuleControlFlag controlFlag = LoginModuleControlFlag.OPTIONAL;
            // kerberos login is mandatory if principal is specified.  principal
            // will not be set for initial default login, but will always be set
            // for relogins.
            final String principal = params.get(LoginParam.PRINCIPAL);
            if (principal != null) {
                options.put("principal", principal);
                controlFlag = LoginModuleControlFlag.REQUIRED;
            }

            // use keytab if given else fallback to ticket cache.
            if (IBM_JAVA) {
                if (params.containsKey(LoginParam.KEYTAB)) {
                    final String keytab = params.get(LoginParam.KEYTAB);
                    if (keytab != null) {
                        options.put("useKeytab", prependFileAuthority(keytab));
                    } else {
                        options.put("useDefaultKeytab", "true");
                    }
                    options.put("credsType", "both");
                } else {
                    String ticketCache = params.get(LoginParam.CCACHE);
                    if (ticketCache != null) {
                        options.put("useCcache", prependFileAuthority(ticketCache));
                    } else {
                        options.put("useDefaultCcache", "true");
                    }
                    options.put("renewTGT", "true");
                }
            } else {
                if (params.containsKey(LoginParam.KEYTAB)) {
                    options.put("useKeyTab", "true");
                    final String keytab = params.get(LoginParam.KEYTAB);
                    if (keytab != null) {
                        options.put("keyTab", keytab);
                    }
                    options.put("storeKey", "true");
                } else {
                    options.put("useTicketCache", "true");
                    String ticketCache = params.get(LoginParam.CCACHE);
                    if (ticketCache != null) {
                        options.put("ticketCache", ticketCache);
                    }
                    options.put("renewTGT", "true");
                }
                options.put("doNotPrompt", "true");
            }
            options.put("refreshKrb5Config", "true");

            return new AppConfigurationEntry(KRB5_LOGIN_MODULE, controlFlag, options);
        }

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

    /**
     * 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.isFromKeytab());
        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);
            UserGroupInformation loginUgi = getLoginUser();
            System.out.println("Auth method " + loginUgi.getAuthenticationMethod());
            System.out.println("Keytab " + loginUgi.isFromKeytab());
        }
    }
}