/*
    *  Licensed to the Apache Software Foundation (ASF) under one
    *  or more contributor license agreements.  See the NOTICE file
    *  distributed with this work for additional information
    *  regarding copyright ownership.  The ASF licenses this file
    *  to you under the Apache License, Version 2.0 (the
    *  "License"); you may not use this file except in compliance
    *  with the License.  You may obtain a copy of the License at
    *  
   *    http://www.apache.org/licenses/LICENSE-2.0
   *  
   *  Unless required by applicable law or agreed to in writing,
   *  software distributed under the License is distributed on an
   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   *  KIND, either express or implied.  See the License for the
   *  specific language governing permissions and limitations
   *  under the License. 
   *  
   */
  package org.apache.directory.server.ldap.handlers.sasl.external.certificate;
  
  
  import org.apache.commons.lang3.exception.ExceptionUtils;
  import org.apache.directory.api.ldap.model.constants.AuthenticationLevel;
  import org.apache.directory.api.ldap.model.constants.SchemaConstants;
  import org.apache.directory.api.ldap.model.constants.SupportedSaslMechanisms;
  import org.apache.directory.api.ldap.model.entry.Entry;
  import org.apache.directory.api.ldap.model.entry.Value;
  import org.apache.directory.api.ldap.model.exception.LdapAuthenticationException;
  import org.apache.directory.api.ldap.model.filter.EqualityNode;
  import org.apache.directory.api.ldap.model.message.BindRequest;
  import org.apache.directory.api.ldap.model.message.SearchScope;
  import org.apache.directory.api.util.Strings;
  import org.apache.directory.server.core.api.CoreSession;
  import org.apache.directory.server.core.api.DirectoryService;
  import org.apache.directory.server.core.api.LdapPrincipal;
  import org.apache.directory.server.core.api.OperationEnum;
  import org.apache.directory.server.core.api.OperationManager;
  import org.apache.directory.server.core.api.filtering.EntryFilteringCursor;
  import org.apache.directory.server.core.api.interceptor.context.BindOperationContext;
  import org.apache.directory.server.core.api.interceptor.context.SearchOperationContext;
  import org.apache.directory.server.ldap.LdapServer;
  import org.apache.directory.server.ldap.LdapSession;
  import org.apache.directory.server.ldap.handlers.sasl.AbstractSaslServer;
  import org.apache.directory.server.ldap.handlers.sasl.SaslConstants;
  import org.apache.mina.filter.ssl.SslFilter;
  
  import javax.naming.Context;
  import javax.net.ssl.SSLSession;
  import javax.security.sasl.SaslException;
  import java.security.cert.Certificate;
  
  
  /**
   * A SaslServer implementation for certificate based SASL EXTERNAL mechanism.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public final class ExternalSaslServer extends AbstractSaslServer
  {
      /**
       * The possible states for the negotiation of a EXTERNAL mechanism.
       */
      private enum NegotiationState
      {
          INITIALIZED, // Negotiation has just started
          COMPLETED // The user/password have been received
      }
  
      /** The current negotiation state */
      private NegotiationState state;
  
      /**
       *
       * Creates a new instance of ExternalSaslServer.
       *
       * @param ldapSession The associated LdapSession instance
       * @param adminSession The Administrator session
       * @param bindRequest The associated BindRequest object
       */
      ExternalSaslServer( LdapSession ldapSession, CoreSession adminSession, BindRequest bindRequest )
      {
          super( ldapSession, adminSession, bindRequest );
          state = NegotiationState.INITIALIZED;
      }
  
  
      /**
       * {@inheritDoc}
       */
      public String getMechanismName()
      {
          return SupportedSaslMechanisms.EXTERNAL;
      }
  
  
      /**
       * {@inheritDoc}
       */
     public byte[] evaluateResponse( byte[] initialResponse ) throws SaslException
     {
         try
         {
             SSLSession sslSession = ( SSLSession ) getLdapSession().getIoSession().getAttribute( SslFilter.SSL_SESSION );
             Certificate[] peerCertificates = sslSession.getPeerCertificates();
 
             if ( null == peerCertificates || 1 > peerCertificates.length )
             {
                 throw new SaslException( "No peer certificate provided - cancel bind." );
             }
 
             getLdapSession().setCoreSession( authenticate( peerCertificates[0] ) );
             state = NegotiationState.COMPLETED;
         }
         catch ( Exception e )
         {
             throw new SaslException( "Error authentication using client certificate: " + ExceptionUtils.getStackTrace( e ), e );
         }
         
         return Strings.EMPTY_BYTES;
     }
 
 
     /**
      * Provides {@code true} if negationstate is {@link NegotiationState#COMPLETED}
      *
      * @return {@code true} if completed, otherwise {@code false}
      */
     public boolean isComplete()
     {
         return state == NegotiationState.COMPLETED;
     }
 
 
     /**
      * Try to authenticate the user against the underlying LDAP server.
      * We identify the user using the provided peercertificate.
      */
     private CoreSession authenticate( Certificate peerCertificate ) throws Exception
     {
         LdapSession ldapSession = getLdapSession();
         CoreSession adminSession = getAdminSession();
         DirectoryService directoryService = adminSession.getDirectoryService();
         LdapServer ldapServer = ldapSession.getLdapServer();
         OperationManager operationManager = directoryService.getOperationManager();
 
         // find user by userCertificate
         EqualityNode<String> filter = new EqualityNode<>(
                 directoryService.getSchemaManager().getAttributeType( SchemaConstants.USER_CERTIFICATE_AT ),
                 new Value( peerCertificate.getEncoded() ) );
 
         SearchOperationContext/interceptor/context/SearchOperationContext.html#SearchOperationContext">SearchOperationContext searchContext = new SearchOperationContext( directoryService.getAdminSession() );
         searchContext.setDn( directoryService.getDnFactory().create( ldapServer.getSearchBaseDn() ) );
         searchContext.setScope( SearchScope.SUBTREE );
         searchContext.setFilter( filter );
         searchContext.setSizeLimit( 1 );
         searchContext.setNoAttributes( true );
 
         try ( EntryFilteringCursor cursor = operationManager.search( searchContext ) )
         {
             if ( cursor.next() )
             {
                 Entry entry = cursor.get();
 
                 BindOperationContext/api/interceptor/context/BindOperationContext.html#BindOperationContext">BindOperationContext bindContext = new BindOperationContext( ldapSession.getCoreSession() );
                 bindContext.setDn( entry.getDn() );
                 bindContext.setSaslMechanism( getMechanismName() );
                 bindContext.setSaslAuthId( getBindRequest().getName() );
                 bindContext.setIoSession( ldapSession.getIoSession() );
                 bindContext.setInterceptors( directoryService.getInterceptors( OperationEnum.BIND ) );
 
                 operationManager.bind( bindContext );
 
                 ldapSession.putSaslProperty( SaslConstants.SASL_AUTHENT_USER, new LdapPrincipal( directoryService.getSchemaManager(),
                         entry.getDn(), AuthenticationLevel.STRONG ) );
                 getLdapSession().putSaslProperty( Context.SECURITY_PRINCIPAL, getBindRequest().getName() );
 
                 return bindContext.getSession();
             }
 
             throw new LdapAuthenticationException( "Cannot authenticate user cert=" + peerCertificate );
         }
     }
 }