1 /* 2 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package javax.security.auth.callback; 27 28 /** 29 * <p> An application implements a {@code CallbackHandler} and passes 30 * it to underlying security services so that they may interact with 31 * the application to retrieve specific authentication data, 32 * such as usernames and passwords, or to display certain information, 33 * such as error and warning messages. 34 * 35 * <p> CallbackHandlers are implemented in an application-dependent fashion. 36 * For example, implementations for an application with a graphical user 37 * interface (GUI) may pop up windows to prompt for requested information 38 * or to display error messages. An implementation may also choose to obtain 39 * requested information from an alternate source without asking the end user. 40 * 41 * <p> Underlying security services make requests for different types 42 * of information by passing individual Callbacks to the 43 * {@code CallbackHandler}. The {@code CallbackHandler} 44 * implementation decides how to retrieve and display information 45 * depending on the Callbacks passed to it. For example, 46 * if the underlying service needs a username and password to 47 * authenticate a user, it uses a {@code NameCallback} and 48 * {@code PasswordCallback}. The {@code CallbackHandler} 49 * can then choose to prompt for a username and password serially, 50 * or to prompt for both in a single window. 51 * 52 * <p> A default {@code CallbackHandler} class implementation 53 * may be specified by setting the value of the 54 * {@code auth.login.defaultCallbackHandler} security property. 55 * 56 * <p> If the security property is set to the fully qualified name of a 57 * {@code CallbackHandler} implementation class, 58 * then a {@code LoginContext} will load the specified 59 * {@code CallbackHandler} and pass it to the underlying LoginModules. 60 * The {@code LoginContext} only loads the default handler 61 * if it was not provided one. 62 * 63 * <p> All default handler implementations must provide a public 64 * zero-argument constructor. 65 * 66 * @see java.security.Security security properties 67 */ 68 public interface CallbackHandler { 69 70 /** 71 * <p> Retrieve or display the information requested in the 72 * provided Callbacks. 73 * 74 * <p> The {@code handle} method implementation checks the 75 * instance(s) of the {@code Callback} object(s) passed in 76 * to retrieve or display the requested information. 77 * The following example is provided to help demonstrate what an 78 * {@code handle} method implementation might look like. 79 * This example code is for guidance only. Many details, 80 * including proper error handling, are left out for simplicity. 81 * 82 * <pre>{@code 83 * public void handle(Callback[] callbacks) 84 * throws IOException, UnsupportedCallbackException { 85 * 86 * for (int i = 0; i < callbacks.length; i++) { 87 * if (callbacks[i] instanceof TextOutputCallback) { 88 * 89 * // display the message according to the specified type 90 * TextOutputCallback toc = (TextOutputCallback)callbacks[i]; 91 * switch (toc.getMessageType()) { 92 * case TextOutputCallback.INFORMATION: 93 * System.out.println(toc.getMessage()); 94 * break; 95 * case TextOutputCallback.ERROR: 96 * System.out.println("ERROR: " + toc.getMessage()); 97 * break; 98 * case TextOutputCallback.WARNING: 99 * System.out.println("WARNING: " + toc.getMessage()); 100 * break; 101 * default: 102 * throw new IOException("Unsupported message type: " + 103 * toc.getMessageType()); 104 * } 105 * 106 * } else if (callbacks[i] instanceof NameCallback) { 107 * 108 * // prompt the user for a username 109 * NameCallback nc = (NameCallback)callbacks[i]; 110 * 111 * // ignore the provided defaultName 112 * System.err.print(nc.getPrompt()); 113 * System.err.flush(); 114 * nc.setName((new BufferedReader 115 * (new InputStreamReader(System.in))).readLine()); 116 * 117 * } else if (callbacks[i] instanceof PasswordCallback) { 118 * 119 * // prompt the user for sensitive information 120 * PasswordCallback pc = (PasswordCallback)callbacks[i]; 121 * System.err.print(pc.getPrompt()); 122 * System.err.flush(); 123 * pc.setPassword(readPassword(System.in)); 124 * 125 * } else { 126 * throw new UnsupportedCallbackException 127 * (callbacks[i], "Unrecognized Callback"); 128 * } 129 * } 130 * } 131 * 132 * // Reads user password from given input stream. 133 * private char[] readPassword(InputStream in) throws IOException { 134 * // insert code to read a user password from the input stream 135 * } 136 * }</pre> 137 * 138 * @param callbacks an array of {@code Callback} objects provided 139 * by an underlying security service which contains 140 * the information requested to be retrieved or displayed. 141 * 142 * @exception java.io.IOException if an input or output error occurs. <p> 143 * 144 * @exception UnsupportedCallbackException if the implementation of this 145 * method does not support one or more of the Callbacks 146 * specified in the {@code callbacks} parameter. 147 */ 148 void handle(Callback[] callbacks) 149 throws java.io.IOException, UnsupportedCallbackException; 150 } 151
