Source for javax.security.auth.callback.CallbackHandler

   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>&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: }