libjava/javax/security/auth/callback/CallbackHandler.java

   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., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 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>&lt;JAVA_HOME>/lib/security/java.security</code>, where
  70  * <code>&lt;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 }