/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed 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.springframework.security.web.authentication.session;

import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

/**
 * The default implementation of {@link SessionAuthenticationStrategy} when using &lt;
 * Servlet 3.1.
 * <p>
 * Creates a new session for the newly authenticated user if they already have a session
 * (as a defence against session-fixation protection attacks), and copies their session
 * attributes across to the new session. The copying of the attributes can be disabled by
 * setting {@code migrateSessionAttributes} to {@code false} (note that even in this case,
 * internal Spring Security attributes will still be migrated to the new session).
 * <p>
 * This approach will only be effective if your servlet container always assigns a new
 * session Id when a session is invalidated and a new session created by calling
 * {@link HttpServletRequest#getSession()}.
 * <p>
 * <h3>Issues with {@code HttpSessionBindingListener}</h3>
 * <p>
 * The migration of existing attributes to the newly-created session may cause problems if
 * any of the objects implement the {@code HttpSessionBindingListener} interface in a way
 * which makes assumptions about the life-cycle of the object. An example is the use of
 * Spring session-scoped beans, where the initial removal of the bean from the session
 * will cause the {@code DisposableBean} interface to be invoked, in the assumption that
 * the bean is no longer required.
 * <p>
 * We'd recommend that you take account of this when designing your application and do not
 * store attributes which may not function correctly when they are removed and then placed
 * back in the session. Alternatively, you should customize the
 * {@code SessionAuthenticationStrategy} to deal with the issue in an application-specific
 * way.
 *
 * @author Luke Taylor
 * @since 3.0
 */
public class SessionFixationProtectionStrategy extends
		AbstractSessionFixationProtectionStrategy {
	/**
	 * Indicates that the session attributes of an existing session should be migrated to
	 * the new session. Defaults to <code>true</code>.
	 */
	boolean migrateSessionAttributes = true;

	/**
	 * Called to extract the existing attributes from the session, prior to invalidating
	 * it. If {@code migrateAttributes} is set to {@code false}, only Spring Security
	 * attributes will be retained. All application attributes will be discarded.
	 * <p>
	 * You can override this method to control exactly what is transferred to the new
	 * session.
	 *
	 * @param session the session from which the attributes should be extracted
	 * @return the map of session attributes which should be transferred to the new
	 * session
	 */
	protected Map<String, Object> extractAttributes(HttpSession session) {
		return createMigratedAttributeMap(session);
	}

	@Override
	final HttpSession applySessionFixation(HttpServletRequest request) {
		HttpSession session = request.getSession();
		String originalSessionId = session.getId();
		if (logger.isDebugEnabled()) {
			logger.debug("Invalidating session with Id '" + originalSessionId + "' "
					+ (migrateSessionAttributes ? "and" : "without")
					+ " migrating attributes.");
		}

		Map<String, Object> attributesToMigrate = extractAttributes(session);

		session.invalidate();
		session = request.getSession(true); // we now have a new session

		if (logger.isDebugEnabled()) {
			logger.debug("Started new session: " + session.getId());
		}

		transferAttributes(attributesToMigrate, session);
		return session;
	}

	/**
	 * @param attributes the attributes which were extracted from the original session by
	 * {@code extractAttributes}
	 * @param newSession the newly created session
	 */
	void transferAttributes(Map<String, Object> attributes, HttpSession newSession) {
		if (attributes != null) {
			for (Map.Entry<String, Object> entry : attributes.entrySet()) {
				newSession.setAttribute(entry.getKey(), entry.getValue());
			}
		}
	}

	@SuppressWarnings("unchecked")
	private HashMap<String, Object> createMigratedAttributeMap(HttpSession session) {
		HashMap<String, Object> attributesToMigrate = new HashMap<String, Object>();

		Enumeration enumer = session.getAttributeNames();

		while (enumer.hasMoreElements()) {
			String key = (String) enumer.nextElement();
			if (!migrateSessionAttributes && !key.startsWith("SPRING_SECURITY_")) {
				// Only retain Spring Security attributes
				continue;
			}
			attributesToMigrate.put(key, session.getAttribute(key));
		}

		return attributesToMigrate;
	}

	/**
	 * Defines whether attributes should be migrated to a new session or not. Has no
	 * effect if you override the {@code extractAttributes} method.
	 * <p>
	 * Attributes used by Spring Security (to store cached requests, for example) will
	 * still be retained by default, even if you set this value to {@code false}.
	 *
	 * @param migrateSessionAttributes whether the attributes from the session should be
	 * transferred to the new, authenticated session.
	 */
	public void setMigrateSessionAttributes(boolean migrateSessionAttributes) {
		this.migrateSessionAttributes = migrateSessionAttributes;
	}
}
