Java tutorial
/** * 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.flume.sink.kite; import com.google.common.base.Preconditions; import com.google.common.base.Throwables; import java.io.File; import java.io.IOException; import java.security.PrivilegedExceptionAction; import org.apache.hadoop.security.SecurityUtil; import org.apache.hadoop.security.UserGroupInformation; import org.kitesdk.data.DatasetException; import org.kitesdk.data.DatasetIOException; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class KerberosUtil { private static final Logger LOG = LoggerFactory.getLogger(org.apache.flume.sink.kite.KerberosUtil.class); public static class SecurityException extends RuntimeException { private SecurityException(String message) { super(message); } private SecurityException(String message, Throwable cause) { super(message, cause); } private SecurityException(Throwable cause) { super(cause); } } public static UserGroupInformation proxyAs(String username, UserGroupInformation login) { Preconditions.checkArgument(username != null && !username.isEmpty(), "Invalid username: " + String.valueOf(username)); Preconditions.checkArgument(login != null, "Cannot proxy without an authenticated user"); // hadoop impersonation works with or without kerberos security return UserGroupInformation.createProxyUser(username, login); } /** * Static synchronized method for static Kerberos login. <br/> * Static synchronized due to a thundering herd problem when multiple Sinks * attempt to log in using the same principal at the same time with the * intention of impersonating different users (or even the same user). * If this is not controlled, MIT Kerberos v5 believes it is seeing a replay * attach and it returns: * <blockquote>Request is a replay (34) - PROCESS_TGS</blockquote> * In addition, since the underlying Hadoop APIs we are using for * impersonation are static, we define this method as static as well. * * @param principal * Fully-qualified principal to use for authentication. * @param keytab * Location of keytab file containing credentials for principal. * @return Logged-in user * @throws org.apache.flume.sink.kite.KerberosUtil.SecurityException * if login fails. * @throws IllegalArgumentException * if the principal or the keytab is not usable */ public static synchronized UserGroupInformation login(String principal, String keytab) { // resolve the requested principal, if it is present String finalPrincipal = null; if (principal != null && !principal.isEmpty()) { try { // resolves _HOST pattern using standard Hadoop search/replace // via DNS lookup when 2nd argument is empty finalPrincipal = SecurityUtil.getServerPrincipal(principal, ""); } catch (IOException e) { throw new SecurityException("Failed to resolve Kerberos principal", e); } } // check if there is a user already logged in UserGroupInformation currentUser = null; try { currentUser = UserGroupInformation.getLoginUser(); } catch (IOException e) { // not a big deal but this shouldn't typically happen because it will // generally fall back to the UNIX user LOG.debug("Unable to get login user before Kerberos auth attempt", e); } // if the current user is valid (matches the given principal) then use it if (currentUser != null) { if (finalPrincipal == null || finalPrincipal.equals(currentUser.getUserName())) { LOG.debug("Using existing login for {}: {}", finalPrincipal, currentUser); return currentUser; } else { // be cruel and unusual when user tries to login as multiple principals // this isn't really valid with a reconfigure but this should be rare // enough to warrant a restart of the agent JVM // TODO: find a way to interrogate the entire current config state, // since we don't have to be unnecessarily protective if they switch all // HDFS sinks to use a different principal all at once. throw new SecurityException("Cannot use multiple Kerberos principals: " + finalPrincipal + " would replace " + currentUser.getUserName()); } } // prepare for a new login Preconditions.checkArgument(principal != null && !principal.isEmpty(), "Invalid Kerberos principal: " + String.valueOf(principal)); Preconditions.checkNotNull(finalPrincipal, "Resolved principal must not be null"); Preconditions.checkArgument(keytab != null && !keytab.isEmpty(), "Invalid Kerberos keytab: " + String.valueOf(keytab)); File keytabFile = new File(keytab); Preconditions.checkArgument(keytabFile.isFile() && keytabFile.canRead(), "Keytab is not a readable file: " + String.valueOf(keytab)); try { // attempt static kerberos login LOG.debug("Logging in as {} with {}", finalPrincipal, keytab); UserGroupInformation.loginUserFromKeytab(principal, keytab); return UserGroupInformation.getLoginUser(); } catch (IOException e) { throw new SecurityException("Kerberos login failed", e); } } /** * Allow methods to act with the privileges of a login. * * If the login is null, the current privileges will be used. * * @param <T> The return type of the action * @param login UserGroupInformation credentials to use for action * @param action A PrivilegedExceptionAction to perform as another user * @return the T value returned by action.run() */ public static <T> T runPrivileged(UserGroupInformation login, PrivilegedExceptionAction<T> action) { try { if (login == null) { return action.run(); } else { return login.doAs(action); } } catch (IOException ex) { throw new DatasetIOException("Privileged action failed", ex); } catch (InterruptedException ex) { Thread.interrupted(); throw new DatasetException(ex); } catch (Exception ex) { throw Throwables.propagate(ex); } } }