001/* CallbackHandler.java -- base interface for callback handlers. 002 Copyright (C) 2003, Free Software Foundation, Inc. 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038 039package javax.security.auth.callback; 040 041import java.io.IOException; 042 043/** 044 * <p>An application implements a <code>CallbackHandler</code> and passes it to 045 * underlying security services so that they may interact with the application 046 * to retrieve specific authentication data, such as usernames and passwords, or 047 * to display certain information, such as error and warning messages.</p> 048 * 049 * <p><code>CallbackHandler</code>s are implemented in an application-dependent 050 * fashion. For example, implementations for an application with a graphical 051 * user interface (GUI) may pop up windows to prompt for requested information 052 * or to display error messages. An implementation may also choose to obtain 053 * requested information from an alternate source without asking the end user.</p> 054 * 055 * <p>Underlying security services make requests for different types of 056 * information by passing individual Callbacks to the <code>CallbackHandler</code>. 057 * The <code>CallbackHandler</code> implementation decides how to retrieve and 058 * display information depending on the {@link Callback}s passed to it. For 059 * example, if the underlying service needs a username and password to 060 * authenticate a user, it uses a {@link NameCallback} and 061 * {@link PasswordCallback}. The <code>CallbackHandler</code> can then choose 062 * to prompt for a username and password serially, or to prompt for both in a 063 * single window.</p> 064 * 065 * <p>A default <code>CallbackHandler</code> class implementation may be 066 * specified in the <code>auth.login.defaultCallbackHandler</code> security 067 * property. The security property can be set in the Java security properties 068 * file located in the file named 069 * <code><JAVA_HOME>/lib/security/java.security</code>, where 070 * <code><JAVA_HOME></code> refers to the directory where the SDK was 071 * installed.</p> 072 * 073 * <p>If the security property is set to the fully qualified name of a 074 * <code>CallbackHandler</code> implementation class, then a 075 * <code>LoginContext</code>will load the specified <code>CallbackHandler</code> 076 * and pass it to the underlying <code>LoginModules</code>. The 077 * <code>LoginContext</code> only loads the default handler if one was not 078 * provided.</p> 079 * 080 * <p>All default handler implementations must provide a public zero-argument 081 * constructor.</p> 082 * 083 */ 084public interface CallbackHandler 085{ 086 087 /** 088 * <p>Retrieve or display the information requested in the provided 089 * {@link Callback}s.</p> 090 * 091 * <p>The <code>handle()</code> method implementation checks the instance(s) 092 * of the {@link Callback} object(s) passed in to retrieve or display the 093 * requested information. The following example is provided to help 094 * demonstrate what an <code>handle()</code> method implementation might look 095 * like. This example code is for guidance only. Many details, including 096 * proper error handling, are left out for simplicity.</p> 097 * 098 * <pre> 099 *public void handle(Callback[] callbacks) 100 *throws IOException, UnsupportedCallbackException { 101 * for (int i = 0; i < callbacks.length; i++) { 102 * if (callbacks[i] instanceof TextOutputCallback) { 103 * // display the message according to the specified type 104 * TextOutputCallback toc = (TextOutputCallback)callbacks[i]; 105 * switch (toc.getMessageType()) { 106 * case TextOutputCallback.INFORMATION: 107 * System.out.println(toc.getMessage()); 108 * break; 109 * case TextOutputCallback.ERROR: 110 * System.out.println("ERROR: " + toc.getMessage()); 111 * break; 112 * case TextOutputCallback.WARNING: 113 * System.out.println("WARNING: " + toc.getMessage()); 114 * break; 115 * default: 116 * throw new IOException("Unsupported message type: " 117 * + toc.getMessageType()); 118 * } 119 * } else if (callbacks[i] instanceof NameCallback) { 120 * // prompt the user for a username 121 * NameCallback nc = (NameCallback)callbacks[i]; 122 * // ignore the provided defaultName 123 * System.err.print(nc.getPrompt()); 124 * System.err.flush(); 125 * nc.setName((new BufferedReader( 126 * new InputStreamReader(System.in))).readLine()); 127 * } else if (callbacks[i] instanceof PasswordCallback) { 128 * // prompt the user for sensitive information 129 * PasswordCallback pc = (PasswordCallback)callbacks[i]; 130 * System.err.print(pc.getPrompt()); 131 * System.err.flush(); 132 * pc.setPassword(readPassword(System.in)); 133 * } else { 134 * throw new UnsupportedCallbackException( 135 * callbacks[i], "Unrecognized Callback"); 136 * } 137 * } 138 *} 139 * 140 * // Reads user password from given input stream. 141 *private char[] readPassword(InputStream in) throws IOException { 142 * // insert code to read a user password from the input stream 143 *} 144 * </pre> 145 * 146 * @param callbacks an array of {@link Callback} objects provided by an 147 * underlying security service which contains the information requested to 148 * be retrieved or displayed. 149 * @throws IOException if an input or output error occurs. 150 * @throws UnsupportedCallbackException if the implementation of this method 151 * does not support one or more of the Callbacks specified in the 152 * <code>callbacks</code> parameter. 153 */ 154 void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException; 155}