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25  
26  package javax.security.sasl;
27  
28  /**
29   * Performs SASL authentication as a client.
30   *<p>
31   * A protocol library such as one for LDAP gets an instance of this
32   * class in order to perform authentication defined by a specific SASL
33   * mechanism. Invoking methods on the {@code SaslClient} instance
34   * process challenges and create responses according to the SASL
35   * mechanism implemented by the {@code SaslClient}.
36   * As the authentication proceeds, the instance
37   * encapsulates the state of a SASL client's authentication exchange.
38   *<p>
39   * Here's an example of how an LDAP library might use a {@code SaslClient}.
40   * It first gets an instance of a {@code SaslClient}:
41   *<blockquote><pre>{@code
42   * SaslClient sc = Sasl.createSaslClient(mechanisms,
43   *     authorizationId, protocol, serverName, props, callbackHandler);
44   *}</pre></blockquote>
45   * It can then proceed to use the client for authentication.
46   * For example, an LDAP library might use the client as follows:
47   *<blockquote><pre>{@code
48   * // Get initial response and send to server
49   * byte[] response = (sc.hasInitialResponse() ? sc.evaluateChallenge(new byte[0]) :
50   *     null);
51   * LdapResult res = ldap.sendBindRequest(dn, sc.getName(), response);
52   * while (!sc.isComplete() &&
53   *     (res.status == SASL_BIND_IN_PROGRESS || res.status == SUCCESS)) {
54   *     response = sc.evaluateChallenge(res.getBytes());
55   *     if (res.status == SUCCESS) {
56   *         // we're done; don't expect to send another BIND
57   *         if (response != null) {
58   *             throw new SaslException(
59   *                 "Protocol error: attempting to send response after completion");
60   *         }
61   *         break;
62   *     }
63   *     res = ldap.sendBindRequest(dn, sc.getName(), response);
64   * }
65   * if (sc.isComplete() && res.status == SUCCESS) {
66   *    String qop = (String) sc.getNegotiatedProperty(Sasl.QOP);
67   *    if (qop != null
68   *        && (qop.equalsIgnoreCase("auth-int")
69   *            || qop.equalsIgnoreCase("auth-conf"))) {
70   *
71   *      // Use SaslClient.wrap() and SaslClient.unwrap() for future
72   *      // communication with server
73   *      ldap.in = new SecureInputStream(sc, ldap.in);
74   *      ldap.out = new SecureOutputStream(sc, ldap.out);
75   *    }
76   * }
77   *}</pre></blockquote>
78   *
79   * If the mechanism has an initial response, the library invokes
80   * {@code evaluateChallenge()} with an empty
81   * challenge and to get initial response.
82   * Protocols such as IMAP4, which do not include an initial response with
83   * their first authentication command to the server, initiates the
84   * authentication without first calling {@code hasInitialResponse()}
85   * or {@code evaluateChallenge()}.
86   * When the server responds to the command, it sends an initial challenge.
87   * For a SASL mechanism in which the client sends data first, the server should
88   * have issued a challenge with no data. This will then result in a call
89   * (on the client) to {@code evaluateChallenge()} with an empty challenge.
90   *
91   * @since 1.5
92   *
93   * @see Sasl
94   * @see SaslClientFactory
95   *
96   * @author Rosanna Lee
97   * @author Rob Weltman
98   */
99  public abstract interface SaslClient {
100 
101     /**
102      * Returns the IANA-registered mechanism name of this SASL client.
103      * (e.g. "CRAM-MD5", "GSSAPI").
104      * @return A non-null string representing the IANA-registered mechanism name.
105      */
106     public abstract String getMechanismName();
107 
108     /**
109      * Determines whether this mechanism has an optional initial response.
110      * If true, caller should call {@code evaluateChallenge()} with an
111      * empty array to get the initial response.
112      *
113      * @return true if this mechanism has an initial response.
114      */
115     public abstract boolean hasInitialResponse();
116 
117     /**
118      * Evaluates the challenge data and generates a response.
119      * If a challenge is received from the server during the authentication
120      * process, this method is called to prepare an appropriate next
121      * response to submit to the server.
122      *
123      * @param challenge The non-null challenge sent from the server.
124      * The challenge array may have zero length.
125      *
126      * @return The possibly null response to send to the server.
127      * It is null if the challenge accompanied a "SUCCESS" status and the challenge
128      * only contains data for the client to update its state and no response
129      * needs to be sent to the server. The response is a zero-length byte
130      * array if the client is to send a response with no data.
131      * @exception SaslException If an error occurred while processing
132      * the challenge or generating a response.
133      */
134     public abstract byte[] evaluateChallenge(byte[] challenge)
135         throws SaslException;
136 
137     /**
138       * Determines whether the authentication exchange has completed.
139       * This method may be called at any time, but typically, it
140       * will not be called until the caller has received indication
141       * from the server
142       * (in a protocol-specific manner) that the exchange has completed.
143       *
144       * @return true if the authentication exchange has completed; false otherwise.
145       */
146     public abstract boolean isComplete();
147 
148     /**
149      * Unwraps a byte array received from the server.
150      * This method can be called only after the authentication exchange has
151      * completed (i.e., when {@code isComplete()} returns true) and only if
152      * the authentication exchange has negotiated integrity and/or privacy
153      * as the quality of protection; otherwise, an
154      * {@code IllegalStateException} is thrown.
155      *<p>
156      * {@code incoming} is the contents of the SASL buffer as defined in RFC 2222
157      * without the leading four octet field that represents the length.
158      * {@code offset} and {@code len} specify the portion of {@code incoming}
159      * to use.
160      *
161      * @param incoming A non-null byte array containing the encoded bytes
162      *                from the server.
163      * @param offset The starting position at {@code incoming} of the bytes to use.
164      * @param len The number of bytes from {@code incoming} to use.
165      * @return A non-null byte array containing the decoded bytes.
166      * @exception SaslException if {@code incoming} cannot be successfully
167      * unwrapped.
168      * @exception IllegalStateException if the authentication exchange has
169      * not completed, or  if the negotiated quality of protection
170      * has neither integrity nor privacy.
171      */
172     public abstract byte[] unwrap(byte[] incoming, int offset, int len)
173         throws SaslException;
174 
175     /**
176      * Wraps a byte array to be sent to the server.
177      * This method can be called only after the authentication exchange has
178      * completed (i.e., when {@code isComplete()} returns true) and only if
179      * the authentication exchange has negotiated integrity and/or privacy
180      * as the quality of protection; otherwise, an
181      * {@code IllegalStateException} is thrown.
182      *<p>
183      * The result of this method will make up the contents of the SASL buffer
184      * as defined in RFC 2222 without the leading four octet field that
185      * represents the length.
186      * {@code offset} and {@code len} specify the portion of {@code outgoing}
187      * to use.
188      *
189      * @param outgoing A non-null byte array containing the bytes to encode.
190      * @param offset The starting position at {@code outgoing} of the bytes to use.
191      * @param len The number of bytes from {@code outgoing} to use.
192      * @return A non-null byte array containing the encoded bytes.
193      * @exception SaslException if {@code outgoing} cannot be successfully
194      * wrapped.
195      * @exception IllegalStateException if the authentication exchange has
196      * not completed, or if the negotiated quality of protection
197      * has neither integrity nor privacy.
198      */
199     public abstract byte[] wrap(byte[] outgoing, int offset, int len)
200         throws SaslException;
201 
202     /**
203      * Retrieves the negotiated property.
204      * This method can be called only after the authentication exchange has
205      * completed (i.e., when {@code isComplete()} returns true); otherwise, an
206      * {@code IllegalStateException} is thrown.
207      *
208      * @param propName The non-null property name.
209      * @return The value of the negotiated property. If null, the property was
210      * not negotiated or is not applicable to this mechanism.
211      * @exception IllegalStateException if this authentication exchange
212      * has not completed
213      */
214 
215     public abstract Object getNegotiatedProperty(String propName);
216 
217      /**
218       * Disposes of any system resources or security-sensitive information
219       * the SaslClient might be using. Invoking this method invalidates
220       * the SaslClient instance. This method is idempotent.
221       * @throws SaslException If a problem was encountered while disposing
222       * the resources.
223       */
224     public abstract void dispose() throws SaslException;
225 }