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jeremybenn |
/* CallbackHandler.java -- base interface for callback handlers.
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Copyright (C) 2003, Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package javax.security.auth.callback;
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import java.io.IOException;
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/**
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* <p>An application implements a <code>CallbackHandler</code> and passes it to
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* underlying security services so that they may interact with the application
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* to retrieve specific authentication data, such as usernames and passwords, or
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* to display certain information, such as error and warning messages.</p>
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*
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* <p><code>CallbackHandler</code>s are implemented in an application-dependent
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* fashion. For example, implementations for an application with a graphical
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* user interface (GUI) may pop up windows to prompt for requested information
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* or to display error messages. An implementation may also choose to obtain
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* requested information from an alternate source without asking the end user.</p>
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*
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* <p>Underlying security services make requests for different types of
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* information by passing individual Callbacks to the <code>CallbackHandler</code>.
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* The <code>CallbackHandler</code> implementation decides how to retrieve and
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* display information depending on the {@link Callback}s passed to it. For
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* example, if the underlying service needs a username and password to
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* authenticate a user, it uses a {@link NameCallback} and
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* {@link PasswordCallback}. The <code>CallbackHandler</code> can then choose
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* to prompt for a username and password serially, or to prompt for both in a
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* single window.</p>
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*
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* <p>A default <code>CallbackHandler</code> class implementation may be
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* specified in the <code>auth.login.defaultCallbackHandler</code> security
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* property. The security property can be set in the Java security properties
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* file located in the file named
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* <code><JAVA_HOME>/lib/security/java.security</code>, where
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* <code><JAVA_HOME></code> refers to the directory where the SDK was
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* installed.</p>
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*
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* <p>If the security property is set to the fully qualified name of a
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* <code>CallbackHandler</code> implementation class, then a
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* <code>LoginContext</code>will load the specified <code>CallbackHandler</code>
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* and pass it to the underlying <code>LoginModules</code>. The
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* <code>LoginContext</code> only loads the default handler if one was not
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* provided.</p>
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*
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* <p>All default handler implementations must provide a public zero-argument
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* constructor.</p>
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*
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*/
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public interface CallbackHandler
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{
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/**
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* <p>Retrieve or display the information requested in the provided
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* {@link Callback}s.</p>
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*
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* <p>The <code>handle()</code> method implementation checks the instance(s)
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* of the {@link Callback} object(s) passed in to retrieve or display the
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* requested information. The following example is provided to help
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* demonstrate what an <code>handle()</code> method implementation might look
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* like. This example code is for guidance only. Many details, including
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* proper error handling, are left out for simplicity.</p>
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*
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* <pre>
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*public void handle(Callback[] callbacks)
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*throws IOException, UnsupportedCallbackException {
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* for (int i = 0; i < callbacks.length; i++) {
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* if (callbacks[i] instanceof TextOutputCallback) {
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* // display the message according to the specified type
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* TextOutputCallback toc = (TextOutputCallback)callbacks[i];
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* switch (toc.getMessageType()) {
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* case TextOutputCallback.INFORMATION:
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* System.out.println(toc.getMessage());
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* break;
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* case TextOutputCallback.ERROR:
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* System.out.println("ERROR: " + toc.getMessage());
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* break;
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* case TextOutputCallback.WARNING:
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* System.out.println("WARNING: " + toc.getMessage());
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* break;
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* default:
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* throw new IOException("Unsupported message type: "
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* + toc.getMessageType());
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* }
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* } else if (callbacks[i] instanceof NameCallback) {
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* // prompt the user for a username
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* NameCallback nc = (NameCallback)callbacks[i];
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* // ignore the provided defaultName
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* System.err.print(nc.getPrompt());
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* System.err.flush();
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* nc.setName((new BufferedReader(
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* new InputStreamReader(System.in))).readLine());
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* } else if (callbacks[i] instanceof PasswordCallback) {
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* // prompt the user for sensitive information
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* PasswordCallback pc = (PasswordCallback)callbacks[i];
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* System.err.print(pc.getPrompt());
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* System.err.flush();
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* pc.setPassword(readPassword(System.in));
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* } else {
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* throw new UnsupportedCallbackException(
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* callbacks[i], "Unrecognized Callback");
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* }
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* }
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*}
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*
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* // Reads user password from given input stream.
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*private char[] readPassword(InputStream in) throws IOException {
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* // insert code to read a user password from the input stream
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*}
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* </pre>
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*
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* @param callbacks an array of {@link Callback} objects provided by an
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* underlying security service which contains the information requested to
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* be retrieved or displayed.
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* @throws IOException if an input or output error occurs.
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* @throws UnsupportedCallbackException if the implementation of this method
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* does not support one or more of the Callbacks specified in the
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* <code>callbacks</code> parameter.
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*/
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void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException;
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}
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