/*
 * The contents of this file are subject to the terms of the Common Development and
 * Distribution License (the License). You may not use this file except in compliance with the
 * License.
 *
 * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
 * specific language governing permission and limitations under the License.
 *
 * When distributing Covered Software, include this CDDL Header Notice in each file and include
 * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
 * Header, with the fields enclosed by brackets [] replaced by your own identifying
 * information: "Portions Copyright [year] [name of copyright owner]".
 *
 * Copyright 2006-2009 Sun Microsystems, Inc.
 * Portions Copyright 2011-2016 ForgeRock AS.
 */
package org.opends.server.extensions;

import java.security.MessageDigest;
import java.security.SecureRandom;
import java.text.ParseException;
import java.util.Arrays;
import java.util.List;

import org.forgerock.i18n.LocalizableMessage;
import org.forgerock.i18n.LocalizedIllegalArgumentException;
import org.forgerock.i18n.slf4j.LocalizedLogger;
import org.forgerock.opendj.config.server.ConfigChangeResult;
import org.forgerock.opendj.config.server.ConfigException;
import org.forgerock.opendj.ldap.ByteString;
import org.forgerock.opendj.ldap.DN;
import org.forgerock.opendj.ldap.ResultCode;
import org.opends.server.admin.server.ConfigurationChangeListener;
import org.opends.server.admin.std.server.CramMD5SASLMechanismHandlerCfg;
import org.opends.server.admin.std.server.SASLMechanismHandlerCfg;
import org.opends.server.api.AuthenticationPolicyState;
import org.opends.server.api.ClientConnection;
import org.opends.server.api.IdentityMapper;
import org.opends.server.api.SASLMechanismHandler;
import org.opends.server.core.BindOperation;
import org.opends.server.core.DirectoryServer;
import org.opends.server.core.PasswordPolicyState;
import org.opends.server.types.AuthenticationInfo;
import org.opends.server.types.DirectoryException;
import org.opends.server.types.Entry;
import org.opends.server.types.InitializationException;

import static org.opends.messages.ExtensionMessages.*;
import static org.opends.server.util.ServerConstants.*;
import static org.opends.server.util.StaticUtils.*;

/**
 * This class provides an implementation of a SASL mechanism that uses digest
 * authentication via CRAM-MD5.  This is a password-based mechanism that does
 * not expose the password itself over the wire but rather uses an MD5 hash that
 * proves the client knows the password.  This is similar to the DIGEST-MD5
 * mechanism, and the primary differences are that CRAM-MD5 only obtains random
 * data from the server (whereas DIGEST-MD5 uses random data from both the
 * server and the client), CRAM-MD5 does not allow for an authorization ID in
 * addition to the authentication ID where DIGEST-MD5 does, and CRAM-MD5 does
 * not define any integrity and confidentiality mechanisms where DIGEST-MD5
 * does.  This implementation is  based on the proposal defined in
 * draft-ietf-sasl-crammd5-05.
 */
public class CRAMMD5SASLMechanismHandler
       extends SASLMechanismHandler<CramMD5SASLMechanismHandlerCfg>
       implements ConfigurationChangeListener<
                       CramMD5SASLMechanismHandlerCfg>
{
  private static final LocalizedLogger logger = LocalizedLogger.getLoggerForThisClass();

  /** An array filled with the inner pad byte. */
  private byte[] iPad;

  /** An array filled with the outer pad byte. */
  private byte[] oPad;

  /** The current configuration for this SASL mechanism handler. */
  private CramMD5SASLMechanismHandlerCfg currentConfig;

  /** The identity mapper that will be used to map ID strings to user entries. */
  private IdentityMapper<?> identityMapper;

  /** The message digest engine that will be used to create the MD5 digests. */
  private MessageDigest md5Digest;

  /**
   * The lock that will be used to provide threadsafe access to the message
   * digest.
   */
  private Object digestLock;

  /**
   * The random number generator that we will use to create the server challenge.
   */
  private SecureRandom randomGenerator;



  /**
   * Creates a new instance of this SASL mechanism handler.  No initialization
   * should be done in this method, as it should all be performed in the
   * <CODE>initializeSASLMechanismHandler</CODE> method.
   */
  public CRAMMD5SASLMechanismHandler()
  {
    super();
  }



  /** {@inheritDoc} */
  @Override
  public void initializeSASLMechanismHandler(
                   CramMD5SASLMechanismHandlerCfg configuration)
         throws ConfigException, InitializationException
  {
    configuration.addCramMD5ChangeListener(this);
    currentConfig = configuration;

    // Initialize the variables needed for the MD5 digest creation.
    digestLock      = new Object();
    randomGenerator = new SecureRandom();

    try
    {
      md5Digest = MessageDigest.getInstance("MD5");
    }
    catch (Exception e)
    {
      logger.traceException(e);

      LocalizableMessage message =
          ERR_SASLCRAMMD5_CANNOT_GET_MESSAGE_DIGEST.get(getExceptionMessage(e));
      throw new InitializationException(message, e);
    }


    // Create and fill the iPad and oPad arrays.
    iPad = new byte[HMAC_MD5_BLOCK_LENGTH];
    oPad = new byte[HMAC_MD5_BLOCK_LENGTH];
    Arrays.fill(iPad, CRAMMD5_IPAD_BYTE);
    Arrays.fill(oPad, CRAMMD5_OPAD_BYTE);


    // Get the identity mapper that should be used to find users.
    DN identityMapperDN = configuration.getIdentityMapperDN();
    identityMapper = DirectoryServer.getIdentityMapper(identityMapperDN);

    DirectoryServer.registerSASLMechanismHandler(SASL_MECHANISM_CRAM_MD5, this);
  }



  /** {@inheritDoc} */
  @Override
  public void finalizeSASLMechanismHandler()
  {
    currentConfig.removeCramMD5ChangeListener(this);
    DirectoryServer.deregisterSASLMechanismHandler(SASL_MECHANISM_CRAM_MD5);
  }




  /** {@inheritDoc} */
  @Override
  public void processSASLBind(BindOperation bindOperation)
  {
    // The CRAM-MD5 bind process uses two stages.  See if the client provided
    // any credentials.  If not, then we're in the first stage so we'll send the
    // challenge to the client.
    ByteString       clientCredentials = bindOperation.getSASLCredentials();
    ClientConnection clientConnection  = bindOperation.getClientConnection();
    if (clientCredentials == null)
    {
      // The client didn't provide any credentials, so this is the initial
      // request.  Generate some random data to send to the client as the
      // challenge and store it in the client connection so we can verify the
      // credentials provided by the client later.
      byte[] challengeBytes = new byte[16];
      randomGenerator.nextBytes(challengeBytes);
      StringBuilder challengeString = new StringBuilder(18);
      challengeString.append('<');
      for (byte b : challengeBytes)
      {
        challengeString.append(byteToLowerHex(b));
      }
      challengeString.append('>');

      final ByteString challenge = ByteString.valueOfUtf8(challengeString);
      clientConnection.setSASLAuthStateInfo(challenge);
      bindOperation.setServerSASLCredentials(challenge);
      bindOperation.setResultCode(ResultCode.SASL_BIND_IN_PROGRESS);
      return;
    }


    // If we've gotten here, then the client did provide credentials.  First,
    // make sure that we have a stored version of the credentials associated
    // with the client connection.  If not, then it likely means that the client
    // is trying to pull a fast one on us.
    Object saslStateInfo = clientConnection.getSASLAuthStateInfo();
    if (saslStateInfo == null)
    {
      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_NO_STORED_CHALLENGE.get();
      bindOperation.setAuthFailureReason(message);
      return;
    }

    if (! (saslStateInfo instanceof  ByteString))
    {
      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_INVALID_STORED_CHALLENGE.get();
      bindOperation.setAuthFailureReason(message);
      return;
    }

    ByteString  challenge = (ByteString) saslStateInfo;

    // Wipe out the stored challenge so it can't be used again.
    clientConnection.setSASLAuthStateInfo(null);


    // Now look at the client credentials and make sure that we can decode them.
    // It should be a username followed by a space and a digest string.  Since
    // the username itself may contain spaces but the digest string may not,
    // look for the last space and use it as the delimiter.
    String credString = clientCredentials.toString();
    int spacePos = credString.lastIndexOf(' ');
    if (spacePos < 0)
    {
      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_NO_SPACE_IN_CREDENTIALS.get();
      bindOperation.setAuthFailureReason(message);
      return;
    }

    String userName = credString.substring(0, spacePos);
    String digest   = credString.substring(spacePos+1);


    // Look at the digest portion of the provided credentials.  It must have a
    // length of exactly 32 bytes and be comprised only of hex characters.
    if (digest.length() != 2*MD5_DIGEST_LENGTH)
    {
      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_INVALID_DIGEST_LENGTH.get(
              digest.length(),
              2*MD5_DIGEST_LENGTH);
      bindOperation.setAuthFailureReason(message);
      return;
    }

    byte[] digestBytes;
    try
    {
      digestBytes = hexStringToByteArray(digest);
    }
    catch (ParseException pe)
    {
      logger.traceException(pe);

      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_INVALID_DIGEST_CONTENT.get(
              pe.getMessage());
      bindOperation.setAuthFailureReason(message);
      return;
    }


    // Get the user entry for the authentication ID.  Allow for an
    // authentication ID that is just a username (as per the CRAM-MD5 spec), but
    // also allow a value in the authzid form specified in RFC 2829.
    Entry  userEntry    = null;
    String lowerUserName = toLowerCase(userName);
    if (lowerUserName.startsWith("dn:"))
    {
      // Try to decode the user DN and retrieve the corresponding entry.
      DN userDN;
      try
      {
        userDN = DN.valueOf(userName.substring(3));
      }
      catch (LocalizedIllegalArgumentException e)
      {
        logger.traceException(e);

        bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

        LocalizableMessage message = ERR_SASLCRAMMD5_CANNOT_DECODE_USERNAME_AS_DN.get(userName, e.getMessageObject());
        bindOperation.setAuthFailureReason(message);
        return;
      }

      if (userDN.isRootDN())
      {
        bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

        LocalizableMessage message = ERR_SASLCRAMMD5_USERNAME_IS_NULL_DN.get();
        bindOperation.setAuthFailureReason(message);
        return;
      }

      DN rootDN = DirectoryServer.getActualRootBindDN(userDN);
      if (rootDN != null)
      {
        userDN = rootDN;
      }

      try
      {
        userEntry = DirectoryServer.getEntry(userDN);
      }
      catch (DirectoryException de)
      {
        logger.traceException(de);

        bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

        LocalizableMessage message = ERR_SASLCRAMMD5_CANNOT_GET_ENTRY_BY_DN.get(userDN, de.getMessageObject());
        bindOperation.setAuthFailureReason(message);
        return;
      }
    }
    else
    {
      // Use the identity mapper to resolve the username to an entry.
      if (lowerUserName.startsWith("u:"))
      {
        userName = userName.substring(2);
      }

      try
      {
        userEntry = identityMapper.getEntryForID(userName);
      }
      catch (DirectoryException de)
      {
        logger.traceException(de);

        bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

        LocalizableMessage message = ERR_SASLCRAMMD5_CANNOT_MAP_USERNAME.get(userName, de.getMessageObject());
        bindOperation.setAuthFailureReason(message);
        return;
      }
    }


    // At this point, we should have a user entry.  If we don't then fail.
    if (userEntry == null)
    {
      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_NO_MATCHING_ENTRIES.get(userName);
      bindOperation.setAuthFailureReason(message);
      return;
    }
    else
    {
      bindOperation.setSASLAuthUserEntry(userEntry);
    }


    // Get the clear-text passwords from the user entry, if there are any.
    List<ByteString> clearPasswords;
    try
    {
      AuthenticationPolicyState authState = AuthenticationPolicyState.forUser(
          userEntry, false);

      if (!authState.isPasswordPolicy())
      {
        bindOperation.setResultCode(ResultCode.INAPPROPRIATE_AUTHENTICATION);
        LocalizableMessage message = ERR_SASL_ACCOUNT_NOT_LOCAL
            .get(SASL_MECHANISM_CRAM_MD5, userEntry.getName());
        bindOperation.setAuthFailureReason(message);
        return;
      }

      PasswordPolicyState pwPolicyState = (PasswordPolicyState) authState;
      clearPasswords = pwPolicyState.getClearPasswords();
      if (clearPasswords == null || clearPasswords.isEmpty())
      {
        bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

        LocalizableMessage message = ERR_SASLCRAMMD5_NO_REVERSIBLE_PASSWORDS.get(userEntry.getName());
        bindOperation.setAuthFailureReason(message);
        return;
      }
    }
    catch (Exception e)
    {
      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_CANNOT_GET_REVERSIBLE_PASSWORDS.get( userEntry.getName(), e);
      bindOperation.setAuthFailureReason(message);
      return;
    }


    // Iterate through the clear-text values and see if any of them can be used
    // in conjunction with the challenge to construct the provided digest.
    boolean matchFound = false;
    for (ByteString clearPassword : clearPasswords)
    {
      byte[] generatedDigest = generateDigest(clearPassword, challenge);
      if (Arrays.equals(digestBytes, generatedDigest))
      {
        matchFound = true;
        break;
      }
    }

    if (! matchFound)
    {
      bindOperation.setResultCode(ResultCode.INVALID_CREDENTIALS);

      LocalizableMessage message = ERR_SASLCRAMMD5_INVALID_PASSWORD.get();
      bindOperation.setAuthFailureReason(message);
      return;
    }


    // If we've gotten here, then the authentication was successful.
    bindOperation.setResultCode(ResultCode.SUCCESS);

    AuthenticationInfo authInfo = new AuthenticationInfo(userEntry,
        SASL_MECHANISM_CRAM_MD5, DirectoryServer.isRootDN(userEntry.getName()));
    bindOperation.setAuthenticationInfo(authInfo);
  }



  /**
   * Generates the appropriate HMAC-MD5 digest for a CRAM-MD5 authentication
   * with the given information.
   *
   * @param  password   The clear-text password to use when generating the
   *                    digest.
   * @param  challenge  The server-supplied challenge to use when generating the
   *                    digest.
   *
   * @return  The generated HMAC-MD5 digest for CRAM-MD5 authentication.
   */
  private byte[] generateDigest(ByteString password, ByteString challenge)
  {
    // Get the byte arrays backing the password and challenge.
    byte[] p = password.toByteArray();
    byte[] c = challenge.toByteArray();


    // Grab a lock to protect the MD5 digest generation.
    synchronized (digestLock)
    {
      // If the password is longer than the HMAC-MD5 block length, then use an
      // MD5 digest of the password rather than the password itself.
      if (p.length > HMAC_MD5_BLOCK_LENGTH)
      {
        p = md5Digest.digest(p);
      }


      // Create byte arrays with data needed for the hash generation.
      byte[] iPadAndData = new byte[HMAC_MD5_BLOCK_LENGTH + c.length];
      System.arraycopy(iPad, 0, iPadAndData, 0, HMAC_MD5_BLOCK_LENGTH);
      System.arraycopy(c, 0, iPadAndData, HMAC_MD5_BLOCK_LENGTH, c.length);

      byte[] oPadAndHash = new byte[HMAC_MD5_BLOCK_LENGTH + MD5_DIGEST_LENGTH];
      System.arraycopy(oPad, 0, oPadAndHash, 0, HMAC_MD5_BLOCK_LENGTH);


      // Iterate through the bytes in the key and XOR them with the iPad and
      // oPad as appropriate.
      for (int i=0; i < p.length; i++)
      {
        iPadAndData[i] ^= p[i];
        oPadAndHash[i] ^= p[i];
      }


      // Copy an MD5 digest of the iPad-XORed key and the data into the array to
      // be hashed.
      System.arraycopy(md5Digest.digest(iPadAndData), 0, oPadAndHash,
                       HMAC_MD5_BLOCK_LENGTH, MD5_DIGEST_LENGTH);


      // Return an MD5 digest of the resulting array.
      return md5Digest.digest(oPadAndHash);
    }
  }



  /** {@inheritDoc} */
  @Override
  public boolean isPasswordBased(String mechanism)
  {
    // This is a password-based mechanism.
    return true;
  }



  /** {@inheritDoc} */
  @Override
  public boolean isSecure(String mechanism)
  {
    // This may be considered a secure mechanism.
    return true;
  }



  /** {@inheritDoc} */
  @Override
  public boolean isConfigurationAcceptable(
                      SASLMechanismHandlerCfg configuration,
                      List<LocalizableMessage> unacceptableReasons)
  {
    CramMD5SASLMechanismHandlerCfg config =
         (CramMD5SASLMechanismHandlerCfg) configuration;
    return isConfigurationChangeAcceptable(config, unacceptableReasons);
  }



  /** {@inheritDoc} */
  @Override
  public boolean isConfigurationChangeAcceptable(
                      CramMD5SASLMechanismHandlerCfg configuration,
                      List<LocalizableMessage> unacceptableReasons)
  {
    return true;
  }



  /** {@inheritDoc} */
  @Override
  public ConfigChangeResult applyConfigurationChange(
              CramMD5SASLMechanismHandlerCfg configuration)
  {
    final ConfigChangeResult ccr = new ConfigChangeResult();

    DN identityMapperDN = configuration.getIdentityMapperDN();
    identityMapper = DirectoryServer.getIdentityMapper(identityMapperDN);
    currentConfig  = configuration;

    return ccr;
  }
}