1 /*
2 * Copyright 1999-2005 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package javax.security.auth.callback;
27
28 /**
29 * <p> An application implements a <code>CallbackHandler</code> and passes
30 * it to underlying security services so that they may interact with
31 * the application to retrieve specific authentication data,
32 * such as usernames and passwords, or to display certain information,
33 * such as error and warning messages.
34 *
35 * <p> CallbackHandlers are implemented in an application-dependent fashion.
36 * For example, implementations for an application with a graphical user
37 * interface (GUI) may pop up windows to prompt for requested information
38 * or to display error messages. An implementation may also choose to obtain
39 * requested information from an alternate source without asking the end user.
40 *
41 * <p> Underlying security services make requests for different types
42 * of information by passing individual Callbacks to the
43 * <code>CallbackHandler</code>. The <code>CallbackHandler</code>
44 * implementation decides how to retrieve and display information
45 * depending on the Callbacks passed to it. For example,
46 * if the underlying service needs a username and password to
47 * authenticate a user, it uses a <code>NameCallback</code> and
48 * <code>PasswordCallback</code>. The <code>CallbackHandler</code>
49 * can then choose to prompt for a username and password serially,
50 * or to prompt for both in a single window.
51 *
52 * <p> A default <code>CallbackHandler</code> class implementation
53 * may be specified in the <i>auth.login.defaultCallbackHandler</i>
54 * security property. The security property can be set
55 * in the Java security properties file located in the file named
56 * <JAVA_HOME>/lib/security/java.security.
57 * <JAVA_HOME> refers to the value of the java.home system property,
58 * and specifies the directory where the JRE is installed.
59 *
60 * <p> If the security property is set to the fully qualified name of a
61 * <code>CallbackHandler</code> implementation class,
62 * then a <code>LoginContext</code> will load the specified
63 * <code>CallbackHandler</code> and pass it to the underlying LoginModules.
64 * The <code>LoginContext</code> only loads the default handler
65 * if it was not provided one.
66 *
67 * <p> All default handler implementations must provide a public
68 * zero-argument constructor.
69 *
70 */
71 public interface CallbackHandler {
72
73 /**
74 * <p> Retrieve or display the information requested in the
75 * provided Callbacks.
76 *
77 * <p> The <code>handle</code> method implementation checks the
78 * instance(s) of the <code>Callback</code> object(s) passed in
79 * to retrieve or display the requested information.
80 * The following example is provided to help demonstrate what an
81 * <code>handle</code> method implementation might look like.
82 * This example code is for guidance only. Many details,
83 * including proper error handling, are left out for simplicity.
84 *
85 * <pre>
86 * public void handle(Callback[] callbacks)
87 * throws IOException, UnsupportedCallbackException {
88 *
89 * for (int i = 0; i < callbacks.length; i++) {
90 * if (callbacks[i] instanceof TextOutputCallback) {
91 *
92 * // display the message according to the specified type
93 * TextOutputCallback toc = (TextOutputCallback)callbacks[i];
94 * switch (toc.getMessageType()) {
95 * case TextOutputCallback.INFORMATION:
96 * System.out.println(toc.getMessage());
97 * break;
98 * case TextOutputCallback.ERROR:
99 * System.out.println("ERROR: " + toc.getMessage());
100 * break;
101 * case TextOutputCallback.WARNING:
102 * System.out.println("WARNING: " + toc.getMessage());
103 * break;
104 * default:
105 * throw new IOException("Unsupported message type: " +
106 * toc.getMessageType());
107 * }
108 *
109 * } else if (callbacks[i] instanceof NameCallback) {
110 *
111 * // prompt the user for a username
112 * NameCallback nc = (NameCallback)callbacks[i];
113 *
114 * // ignore the provided defaultName
115 * System.err.print(nc.getPrompt());
116 * System.err.flush();
117 * nc.setName((new BufferedReader
118 * (new InputStreamReader(System.in))).readLine());
119 *
120 * } else if (callbacks[i] instanceof PasswordCallback) {
121 *
122 * // prompt the user for sensitive information
123 * PasswordCallback pc = (PasswordCallback)callbacks[i];
124 * System.err.print(pc.getPrompt());
125 * System.err.flush();
126 * pc.setPassword(readPassword(System.in));
127 *
128 * } else {
129 * throw new UnsupportedCallbackException
130 * (callbacks[i], "Unrecognized Callback");
131 * }
132 * }
133 * }
134 *
135 * // Reads user password from given input stream.
136 * private char[] readPassword(InputStream in) throws IOException {
137 * // insert code to read a user password from the input stream
138 * }
139 * </pre>
140 *
141 * @param callbacks an array of <code>Callback</code> objects provided
142 * by an underlying security service which contains
143 * the information requested to be retrieved or displayed.
144 *
145 * @exception java.io.IOException if an input or output error occurs. <p>
146 *
147 * @exception UnsupportedCallbackException if the implementation of this
148 * method does not support one or more of the Callbacks
149 * specified in the <code>callbacks</code> parameter.
150 */
151 void handle(Callback[] callbacks)
152 throws java.io.IOException, UnsupportedCallbackException;
153 }
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