/*
    * 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.syncope.sra.security.saml2;
  
  import java.net.URI;
  import org.apache.syncope.sra.security.pac4j.NoOpSessionStore;
  import org.apache.syncope.sra.security.pac4j.ServerWebExchangeContext;
  import org.apache.syncope.sra.security.web.server.DoNothingIfCommittedServerRedirectStrategy;
  import org.apache.syncope.sra.session.SessionUtils;
  import org.pac4j.saml.client.SAML2Client;
  import org.pac4j.saml.credentials.SAML2Credentials;
  import org.springframework.security.authentication.ReactiveAuthenticationManager;
  import org.springframework.security.core.Authentication;
  import org.springframework.security.web.server.ServerRedirectStrategy;
  import org.springframework.security.web.server.WebFilterExchange;
  import org.springframework.security.web.server.authentication.AuthenticationWebFilter;
  import org.springframework.security.web.server.authentication.ServerAuthenticationConverter;
  import org.springframework.security.web.server.authentication.ServerAuthenticationSuccessHandler;
  import org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcher;
  import org.springframework.security.web.server.util.matcher.ServerWebExchangeMatchers;
  import org.springframework.web.server.ServerWebExchange;
  import org.springframework.web.server.WebFilterChain;
  import reactor.core.publisher.Mono;
  
  public class SAML2WebSsoAuthenticationWebFilter extends AuthenticationWebFilter {
  
      public static final String FILTER_PROCESSES_URI = "/login/saml2/sso";
  
      private static final ServerWebExchangeMatcher MATCHER =
              ServerWebExchangeMatchers.pathMatchers(FILTER_PROCESSES_URI);
  
      private final SAML2Client saml2Client;
  
      public SAML2WebSsoAuthenticationWebFilter(
              final ReactiveAuthenticationManager authenticationManager,
              final SAML2Client saml2Client) {
  
          super(authenticationManager);
  
          this.saml2Client = saml2Client;
  
          setRequiresAuthenticationMatcher(matchSamlResponse());
  
          setServerAuthenticationConverter(convertSamlResponse());
  
          setAuthenticationSuccessHandler(redirectToInitialRequestURI());
      }
  
      @Override
      public Mono<Void> filter(final ServerWebExchange exchange, final WebFilterChain chain) {
          return super.filter(exchange, chain).then(Mono.defer(exchange.getResponse()::setComplete));
      }
  
      private ServerWebExchangeMatcher matchSamlResponse() {
          return exchange -> exchange.getFormData().
                  filter(form -> form.containsKey("SAMLResponse")).
                  flatMap(form -> ServerWebExchangeMatcher.MatchResult.match()).
                  switchIfEmpty(ServerWebExchangeMatcher.MatchResult.notMatch());
      }
  
      private ServerAuthenticationConverter convertSamlResponse() {
          return exchange -> exchange.getFormData().
                  flatMap(form -> MATCHER.matches(exchange).
                  flatMap(matchResult -> {
                      ServerWebExchangeContext swec = new ServerWebExchangeContext(exchange).setForm(form);
  
                      SAML2Credentials credentials = (SAML2Credentials) saml2Client.getCredentialsExtractor().
                          extract(swec, NoOpSessionStore.INSTANCE).
                              orElseThrow(() -> new IllegalStateException("No AuthnResponse found"));
  
                      saml2Client.getAuthenticator().validate(credentials, swec, NoOpSessionStore.INSTANCE);
  
                      return Mono.just(new SAML2AuthenticationToken(credentials));
                  }));
      }
  
      private ServerAuthenticationSuccessHandler redirectToInitialRequestURI() {
          return new ServerAuthenticationSuccessHandler() {
  
              private final ServerRedirectStrategy redirectStrategy = new DoNothingIfCommittedServerRedirectStrategy();
  
              @Override
              public Mono<Void> onAuthenticationSuccess(
                     final WebFilterExchange webFilterExchange, final Authentication authentication) {
 
                 return webFilterExchange.getExchange().getSession().
                         flatMap(session -> this.redirectStrategy.sendRedirect(
                         webFilterExchange.getExchange(),
                         session.<URI>getRequiredAttribute(SessionUtils.INITIAL_REQUEST_URI)));
             }
         };
     }
 }