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/* SaslClient.java --

   Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package javax.security.sasl;

/**

 * <p>Performs SASL authentication as a client.</p>

 *

 * <p>A protocol library such as one for LDAP gets an instance of this class in

 * order to perform authentication defined by a specific SASL mechanism.

 * Invoking methods on the <code>SaslClient</code> instance process challenges

 * and create responses according to the SASL mechanism implemented by the

 * <code>SaslClient</code>. As the authentication proceeds, the instance

 * encapsulates the state of a SASL client's authentication exchange.</p>

 *

 * <p>Here's an example of how an LDAP library might use a <code>SaslClient</code>.

 * It first gets an instance of a SaslClient:</p>

 * <pre>

 *SaslClient sc =

 *      Sasl.createSaslClient(mechanisms, authorizationID, protocol,

 *                            serverName, props, callbackHandler);

 * </pre>

 *

 * <p>It can then proceed to use the client for authentication. For example, an

 * LDAP library might use the client as follows:</p>

 * <pre>

 * // Get initial response and send to server

 *byte[] response = sc.hasInitialResponse()

 *      ? sc.evaluateChallenge(new byte[0]) : null;

 *LdapResult res = ldap.sendBindRequest(dn, sc.getName(), response);

 *while (!sc.isComplete()

 *       && ((res.status == SASL_BIND_IN_PROGRESS) || (res.status == SUCCESS))) {

 *   response = sc.evaluateChallenge( res.getBytes() );

 *   if (res.status == SUCCESS) {

 *      // we're done; don't expect to send another BIND

 *      if ( response != null ) {

 *         throw new SaslException(

 *               "Protocol error: attempting to send response after completion");

 *      }

 *      break;

 *   }

 *   res = ldap.sendBindRequest(dn, sc.getName(), response);

 *}

 *if (sc.isComplete() && (res.status == SUCCESS) ) {

 *   String qop = (String)sc.getNegotiatedProperty(Sasl.QOP);

 *   if ((qop != null)

 *         && (qop.equalsIgnoreCase("auth-int")

 *            || qop.equalsIgnoreCase("auth-conf"))) {

 *      // Use SaslClient.wrap() and SaslClient.unwrap() for future

 *      // communication with server

 *      ldap.in = new SecureInputStream(sc, ldap.in);

 *      ldap.out = new SecureOutputStream(sc, ldap.out);

 *   }

 *}

 * </pre>

 *

 * <p>If the mechanism has an initial response, the library invokes

 * {@link #evaluateChallenge(byte[])} with an empty challenge to get the initial

 * response. Protocols such as IMAP4, which do not include an initial response

 * with their first authentication command to the server, initiate the

 * authentication without first calling {@link #hasInitialResponse()} or

 * {@link #evaluateChallenge(byte[])}. When the server responds to the command,

 * it sends an initial challenge. For a SASL mechanism in which the client sends

 * data first, the server should have issued a challenge with no data. This will

 * then result in a call (on the client) to {@link #evaluateChallenge(byte[])}

 * with an empty challenge.</p>

 *

 * @see Sasl

 * @see SaslClientFactory

 *

 * @since 1.5

 */

public interface SaslClient

{

  /**

   * Returns the IANA-registered mechanism name of this SASL client. (e.g.

   * "CRAM-MD5", "GSSAPI").

   *

   * @return a non-null string representing the IANA-registered mechanism name.

   */

  String getMechanismName();

  /**

   * Determines if this mechanism has an optional initial response. If

   * <code>true</code>, caller should call {@link #evaluateChallenge(byte[])}

   * with an empty array to get the initial response.

   *

   * @return <code>true</code> if this mechanism has an initial response.

   */

  boolean hasInitialResponse();

  /**

   * Evaluates the challenge data and generates a response. If a challenge is

   * received from the server during the authentication process, this method is

   * called to prepare an appropriate next response to submit to the server.

   *

   * @param challenge the non-null challenge sent from the server. The

   * challenge array may have zero length.

   * @return the possibly <code>null</code> reponse to send to the server. It

   * is <code>null</code> if the challenge accompanied a "SUCCESS" status and

   * the challenge only contains data for the client to update its state and no

   * response needs to be sent to the server. The response is a zero-length

   * byte array if the client is to send a response with no data.

   * @throws SaslException if an error occurred while processing the challenge

   * or generating a response.

   */

  byte[] evaluateChallenge(byte[] challenge) throws SaslException;

  /**

   * Determines if the authentication exchange has completed. This method may

   * be called at any time, but typically, it will not be called until the

   * caller has received indication from the server (in a protocol-specific

   * manner) that the exchange has completed.

   *

   * @return <code>true</code> if the authentication exchange has completed;

   * <code>false</code> otherwise.

   */

  boolean isComplete();

  /**

   * <p>Unwraps a byte array received from the server. This method can be

   * called only after the authentication exchange has completed (i.e., when

   * {@link #isComplete()} returns <code>true</code>) and only if the

   * authentication exchange has negotiated integrity and/or privacy as the

   * quality of protection; otherwise, an {@link IllegalStateException} is

   * thrown.</p>

   *

   * <p><code>incoming</code> is the contents of the SASL buffer as defined in

   * RFC 2222 without the leading four octet field that represents the length.

   * <code>offset</code> and <code>len</code> specify the portion of incoming

   * to use.</p>

   *

   * @param incoming a non-null byte array containing the encoded bytes from

   * the server.

   * @param offset the starting position at <code>incoming</code> of the bytes

   * to use.

   * @param len the number of bytes from <code>incoming</code> to use.

   * @return a non-null byte array containing the decoded bytes.

   * @throws SaslException if <code>incoming</code> cannot be successfully

   * unwrapped.

   * @throws IllegalStateException if the authentication exchange has not

   * completed, or if the negotiated quality of protection has neither

   * integrity nor privacy.

   */

  byte[] unwrap(byte[] incoming, int offset, int len) throws SaslException;

  /**

   * <p>Wraps a byte array to be sent to the server. This method can be called

   * only after the authentication exchange has completed (i.e., when

   * {@link #isComplete()} returns <code>true</code>) and only if the

   * authentication exchange has negotiated integrity and/or privacy as the

   * quality of protection; otherwise, an {@link IllegalStateException} is

   * thrown.</p>

   *

   * <p>The result of this method will make up the contents of the SASL buffer

   * as defined in RFC 2222 without the leading four octet field that

   * represents the length. <code>offset</code> and <code>len</code> specify

   * the portion of <code>outgoing</code> to use.</p>

   *

   * @param outgoing a non-null byte array containing the bytes to encode.

   * @param offset the starting position at <code>outgoing</code> of the bytes

   * to use.

   * @param len the number of bytes from <code>outgoing</code> to use.

   * @return a non-null byte array containing the encoded bytes.

   * @throws SaslException if <code>outgoing</code> cannot be successfully

   * wrapped.

   * @throws IllegalStateException if the authentication exchange has not

   * completed, or if the negotiated quality of protection has neither

   * integrity nor privacy.

   */

  byte[] wrap(byte[] outgoing, int offset, int len) throws SaslException;

  /**

   * Retrieves the negotiated property. This method can be called only after

   * the authentication exchange has completed (i.e., when {@link #isComplete()}

   * returns <code>true</code>); otherwise, an {@link IllegalStateException} is

   * thrown.

   *

   * @param propName the non-null property name.

   * @return the value of the negotiated property. If <code>null</code>, the

   * property was not negotiated or is not applicable to this mechanism.

   * @throws IllegalStateException if this authentication exchange has not

   * completed.

   */

  Object getNegotiatedProperty(String propName);

  /**

   * Disposes of any system resources or security-sensitive information the

   * <code>SaslClient</code> might be using. Invoking this method invalidates

   * the <code>SaslClient</code> instance. This method is idempotent.

   *

   * @throws SaslException if a problem was encountered while disposing of the

   * resources.

   */

  void dispose() throws SaslException;

}