1: /* CallbackHandler.java -- base interface for callback handlers. 2: Copyright (C) 2003, Free Software Foundation, Inc. 3: 4: This file is part of GNU Classpath. 5: 6: GNU Classpath is free software; you can redistribute it and/or modify 7: it under the terms of the GNU General Public License as published by 8: the Free Software Foundation; either version 2, or (at your option) 9: any later version. 10: 11: GNU Classpath is distributed in the hope that it will be useful, but 12: WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: General Public License for more details. 15: 16: You should have received a copy of the GNU General Public License 17: along with GNU Classpath; see the file COPYING. If not, write to the 18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19: 02110-1301 USA. 20: 21: Linking this library statically or dynamically with other modules is 22: making a combined work based on this library. Thus, the terms and 23: conditions of the GNU General Public License cover the whole 24: combination. 25: 26: As a special exception, the copyright holders of this library give you 27: permission to link this library with independent modules to produce an 28: executable, regardless of the license terms of these independent 29: modules, and to copy and distribute the resulting executable under 30: terms of your choice, provided that you also meet, for each linked 31: independent module, the terms and conditions of the license of that 32: module. An independent module is a module which is not derived from 33: or based on this library. If you modify this library, you may extend 34: this exception to your version of the library, but you are not 35: obligated to do so. If you do not wish to do so, delete this 36: exception statement from your version. */ 37: 38: 39: package javax.security.auth.callback; 40: 41: import java.io.IOException; 42: 43: /** 44: * <p>An application implements a <code>CallbackHandler</code> and passes it to 45: * underlying security services so that they may interact with the application 46: * to retrieve specific authentication data, such as usernames and passwords, or 47: * to display certain information, such as error and warning messages.</p> 48: * 49: * <p><code>CallbackHandler</code>s are implemented in an application-dependent 50: * fashion. For example, implementations for an application with a graphical 51: * user interface (GUI) may pop up windows to prompt for requested information 52: * or to display error messages. An implementation may also choose to obtain 53: * requested information from an alternate source without asking the end user.</p> 54: * 55: * <p>Underlying security services make requests for different types of 56: * information by passing individual Callbacks to the <code>CallbackHandler</code>. 57: * The <code>CallbackHandler</code> implementation decides how to retrieve and 58: * display information depending on the {@link Callback}s passed to it. For 59: * example, if the underlying service needs a username and password to 60: * authenticate a user, it uses a {@link NameCallback} and 61: * {@link PasswordCallback}. The <code>CallbackHandler</code> can then choose 62: * to prompt for a username and password serially, or to prompt for both in a 63: * single window.</p> 64: * 65: * <p>A default <code>CallbackHandler</code> class implementation may be 66: * specified in the <code>auth.login.defaultCallbackHandler</code> security 67: * property. The security property can be set in the Java security properties 68: * file located in the file named 69: * <code><JAVA_HOME>/lib/security/java.security</code>, where 70: * <code><JAVA_HOME></code> refers to the directory where the SDK was 71: * installed.</p> 72: * 73: * <p>If the security property is set to the fully qualified name of a 74: * <code>CallbackHandler</code> implementation class, then a 75: * <code>LoginContext</code>will load the specified <code>CallbackHandler</code> 76: * and pass it to the underlying <code>LoginModules</code>. The 77: * <code>LoginContext</code> only loads the default handler if one was not 78: * provided.</p> 79: * 80: * <p>All default handler implementations must provide a public zero-argument 81: * constructor.</p> 82: * 83: */ 84: public interface CallbackHandler 85: { 86: 87: /** 88: * <p>Retrieve or display the information requested in the provided 89: * {@link Callback}s.</p> 90: * 91: * <p>The <code>handle()</code> method implementation checks the instance(s) 92: * of the {@link Callback} object(s) passed in to retrieve or display the 93: * requested information. The following example is provided to help 94: * demonstrate what an <code>handle()</code> method implementation might look 95: * like. This example code is for guidance only. Many details, including 96: * proper error handling, are left out for simplicity.</p> 97: * 98: * <pre> 99: *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: }