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

/* CallbackHandler.java -- base interface for callback handlers.
   Copyright (C) 2003, Free Software Foundation, Inc.

This file is part of GNU Classpath.

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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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this exception to your version of the library, but you are not
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package javax.security.auth.callback;

import java.io.IOException;

/**
 * <p>An application implements a <code>CallbackHandler</code> and passes it to
 * underlying security services so that they may interact with the application
 * to retrieve specific authentication data, such as usernames and passwords, or
 * to display certain information, such as error and warning messages.</p>
 *
 * <p><code>CallbackHandler</code>s are implemented in an application-dependent
 * fashion. For example, implementations for an application with a graphical
 * user interface (GUI) may pop up windows to prompt for requested information
 * or to display error messages. An implementation may also choose to obtain
 * requested information from an alternate source without asking the end user.</p>
 *
 * <p>Underlying security services make requests for different types of
 * information by passing individual Callbacks to the <code>CallbackHandler</code>.
 * The <code>CallbackHandler</code> implementation decides how to retrieve and
 * display information depending on the {@link Callback}s passed to it. For
 * example, if the underlying service needs a username and password to
 * authenticate a user, it uses a {@link NameCallback} and
 * {@link PasswordCallback}. The <code>CallbackHandler</code> can then choose
 * to prompt for a username and password serially, or to prompt for both in a
 * single window.</p>
 *
 * <p>A default <code>CallbackHandler</code> class implementation may be
 * specified in the <code>auth.login.defaultCallbackHandler</code> security
 * property. The security property can be set in the Java security properties
 * file located in the file named
 * <code>&lt;JAVA_HOME>/lib/security/java.security</code>, where
 * <code>&lt;JAVA_HOME></code> refers to the directory where the SDK was
 * installed.</p>
 *
 * <p>If the security property is set to the fully qualified name of a
 * <code>CallbackHandler</code> implementation class, then a
 * <code>LoginContext</code>will load the specified <code>CallbackHandler</code>
 * and pass it to the underlying <code>LoginModules</code>. The
 * <code>LoginContext</code> only loads the default handler if one was not
 * provided.</p>
 *
 * <p>All default handler implementations must provide a public zero-argument
 * constructor.</p>
 *
 */
public interface CallbackHandler
{

  /**
   * <p>Retrieve or display the information requested in the provided
   * {@link Callback}s.</p>
   *
   * <p>The <code>handle()</code> method implementation checks the instance(s)
   * of the {@link Callback} object(s) passed in to retrieve or display the
   * requested information. The following example is provided to help
   * demonstrate what an <code>handle()</code> method implementation might look
   * like. This example code is for guidance only. Many details, including
   * proper error handling, are left out for simplicity.</p>
   *
   * <pre>
   *public void handle(Callback[] callbacks)
   *throws IOException, UnsupportedCallbackException {
   *   for (int i = 0; i < callbacks.length; i++) {
   *      if (callbacks[i] instanceof TextOutputCallback) {
   *         // display the message according to the specified type
   *         TextOutputCallback toc = (TextOutputCallback)callbacks[i];
   *         switch (toc.getMessageType()) {
   *         case TextOutputCallback.INFORMATION:
   *            System.out.println(toc.getMessage());
   *            break;
   *         case TextOutputCallback.ERROR:
   *            System.out.println("ERROR: " + toc.getMessage());
   *            break;
   *         case TextOutputCallback.WARNING:
   *            System.out.println("WARNING: " + toc.getMessage());
   *            break;
   *         default:
   *            throw new IOException("Unsupported message type: "
   *                  + toc.getMessageType());
   *         }
   *      } else if (callbacks[i] instanceof NameCallback) {
   *         // prompt the user for a username
   *         NameCallback nc = (NameCallback)callbacks[i];
   *         // ignore the provided defaultName
   *         System.err.print(nc.getPrompt());
   *         System.err.flush();
   *         nc.setName((new BufferedReader(
   *               new InputStreamReader(System.in))).readLine());
   *      } else if (callbacks[i] instanceof PasswordCallback) {
   *         // prompt the user for sensitive information
   *         PasswordCallback pc = (PasswordCallback)callbacks[i];
   *         System.err.print(pc.getPrompt());
   *         System.err.flush();
   *         pc.setPassword(readPassword(System.in));
   *      } else {
   *         throw new UnsupportedCallbackException(
   *               callbacks[i], "Unrecognized Callback");
   *      }
   *   }
   *}
   *
   * // Reads user password from given input stream.
   *private char[] readPassword(InputStream in) throws IOException {
   *   // insert code to read a user password from the input stream
   *}
   * </pre>
   *
   * @param callbacks an array of {@link Callback} objects provided by an
   * underlying security service which contains the information requested to
   * be retrieved or displayed.
   * @throws IOException if an input or output error occurs.
   * @throws UnsupportedCallbackException if the implementation of this method
   * does not support one or more of the Callbacks specified in the
   * <code>callbacks</code> parameter.
   */
  void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException;
}