# Interface SaslClient

public interface SaslClient
Performs SASL authentication as a client.

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 `SaslClient` instance process challenges and create responses according to the SASL mechanism implemented by the `SaslClient`. As the authentication proceeds, the instance encapsulates the state of a SASL client's authentication exchange.

Here's an example of how an LDAP library might use a `SaslClient`. It first gets an instance of a `SaslClient`:

>      SaslClient sc = Sasl.createSaslClient(mechanisms,
>          authorizationId, protocol, serverName, props, callbackHandler);

It can then proceed to use the client for authentication. For example, an LDAP library might use the client as follows:

>      // 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);
>         }
>      }

If the mechanism has an initial response, the library invokes `evaluateChallenge()` with an empty challenge and to get initial response. Protocols such as IMAP4, which do not include an initial response with their first authentication command to the server, initiates the authentication without first calling `hasInitialResponse()` or `evaluateChallenge()`. 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 `evaluateChallenge()` with an empty challenge.

Since:
  1.5
See Also:
  - `Sasl`
  - `SaslClientFactory`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `dispose()`
  Disposes of any system resources or security-sensitive information the SaslClient might be using.
  `byte[]`
  `evaluateChallenge(byte[] challenge)`
  Evaluates the challenge data and generates a response.
  `String`
  `getMechanismName()`
  Returns the IANA-registered mechanism name of this SASL client.
  `Object`
  `getNegotiatedProperty(String propName)`
  Retrieves the negotiated property.
  `boolean`
  `hasInitialResponse()`
  Determines whether this mechanism has an optional initial response.
  `boolean`
  `isComplete()`
  Determines whether the authentication exchange has completed.
  `byte[]`
  `unwrap(byte[] incoming, int offset, int len)`
  Unwraps a byte array received from the server.
  `byte[]`
  `wrap(byte[] outgoing, int offset, int len)`
  Wraps a byte array to be sent to the server.

- ## Method Details

  - ### getMechanismName

    String getMechanismName()
    Returns the IANA-registered mechanism name of this SASL client. (e.g. "CRAM-MD5", "GSSAPI").
    Returns:
      A non-null string representing the IANA-registered mechanism name.

  - ### hasInitialResponse

    boolean hasInitialResponse()
    Determines whether this mechanism has an optional initial response. If true, caller should call `evaluateChallenge()` with an empty array to get the initial response.
    Returns:
      true if this mechanism has an initial response.

  - ### evaluateChallenge

    byte[] evaluateChallenge(byte[] challenge) throws SaslException
    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.
    Parameters:
      `challenge` - The non-null challenge sent from the server. The challenge array may have zero length.
    Returns:
      The possibly null response to send to the server. It is null 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.

  - ### isComplete

    boolean isComplete()
    Determines whether 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.
    Returns:
      true if the authentication exchange has completed; false otherwise.

  - ### unwrap

    byte[] unwrap(byte[] incoming, int offset, int len) throws SaslException
    Unwraps a byte array received from the server. This method can be called only after the authentication exchange has completed (i.e., when `isComplete()` returns true) and only if the authentication exchange has negotiated integrity and/or privacy as the quality of protection; otherwise, an `IllegalStateException` is thrown.

    `incoming` is the contents of the SASL buffer as defined in RFC 2222 without the leading four octet field that represents the length. `offset` and `len` specify the portion of `incoming` to use.

    Parameters:
      `incoming` - A non-null byte array containing the encoded bytes from the server.
      `offset` - The starting position at `incoming` of the bytes to use.
      `len` - The number of bytes from `incoming` to use.
    Returns:
      A non-null byte array containing the decoded bytes.
    Throws:
      `SaslException` - if `incoming` cannot be successfully unwrapped.
      `IllegalStateException` - if the authentication exchange has not completed, or if the negotiated quality of protection has neither integrity nor privacy.

  - ### wrap

    byte[] wrap(byte[] outgoing, int offset, int len) throws SaslException
    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 `isComplete()` returns true) and only if the authentication exchange has negotiated integrity and/or privacy as the quality of protection; otherwise, an `IllegalStateException` is thrown.

    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. `offset` and `len` specify the portion of `outgoing` to use.

    Parameters:
      `outgoing` - A non-null byte array containing the bytes to encode.
      `offset` - The starting position at `outgoing` of the bytes to use.
      `len` - The number of bytes from `outgoing` to use.
    Returns:
      A non-null byte array containing the encoded bytes.
    Throws:
      `SaslException` - if `outgoing` cannot be successfully wrapped.
      `IllegalStateException` - if the authentication exchange has not completed, or if the negotiated quality of protection has neither integrity nor privacy.

  - ### getNegotiatedProperty

    Object getNegotiatedProperty(String propName)
    Retrieves the negotiated property. This method can be called only after the authentication exchange has completed (i.e., when `isComplete()` returns true); otherwise, an `IllegalStateException` is thrown.

    The `Sasl` class includes several well-known property names (For example, `Sasl.QOP`). A SASL provider can support other properties which are specific to the vendor and/or a mechanism.

    Parameters:
      `propName` - The non-null property name.
    Returns:
      The value of the negotiated property. If null, the property was not negotiated or is not applicable to this mechanism.
    Throws:
      `IllegalStateException` - if this authentication exchange has not completed

  - ### dispose

    void dispose() throws SaslException
    Disposes of any system resources or security-sensitive information the SaslClient might be using. Invoking this method invalidates the SaslClient instance. This method is idempotent.
    Throws:
      `SaslException` - If a problem was encountered while disposing the resources.