/*
 * Copyright 2004, 2005, 2006, 2009 Acegi Technology Pty Limited
 *
 * 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.www;

import java.io.IOException;
import java.util.Map;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.context.MessageSource;
import org.springframework.context.MessageSourceAware;
import org.springframework.context.support.MessageSourceAccessor;
import org.springframework.security.authentication.AuthenticationDetailsSource;
import org.springframework.security.authentication.AuthenticationServiceException;
import org.springframework.security.authentication.BadCredentialsException;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.AuthenticationException;
import org.springframework.security.core.SpringSecurityMessageSource;
import org.springframework.security.core.context.SecurityContext;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.userdetails.UserCache;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.core.userdetails.UsernameNotFoundException;
import org.springframework.security.core.userdetails.cache.NullUserCache;
import org.springframework.security.crypto.codec.Base64;
import org.springframework.security.web.authentication.WebAuthenticationDetailsSource;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;
import org.springframework.web.filter.GenericFilterBean;

/**
 * Processes a HTTP request's Digest authorization headers, putting the result into the
 * <code>SecurityContextHolder</code>.
 * <p>
 * For a detailed background on what this filter is designed to process, refer to
 * <a href="http://www.ietf.org/rfc/rfc2617.txt">RFC 2617</a> (which superseded RFC 2069,
 * although this filter support clients that implement either RFC 2617 or RFC 2069).
 * <p>
 * This filter can be used to provide Digest authentication services to both remoting
 * protocol clients (such as Hessian and SOAP) as well as standard user agents (such as
 * Internet Explorer and FireFox).
 * <p>
 * This Digest implementation has been designed to avoid needing to store session state
 * between invocations. All session management information is stored in the "nonce" that
 * is sent to the client by the {@link DigestAuthenticationEntryPoint}.
 * <p>
 * If authentication is successful, the resulting
 * {@link org.springframework.security.core.Authentication Authentication} object will be
 * placed into the <code>SecurityContextHolder</code>.
 * <p>
 * If authentication fails, an
 * {@link org.springframework.security.web.AuthenticationEntryPoint
 * AuthenticationEntryPoint} implementation is called. This must always be
 * {@link DigestAuthenticationEntryPoint}, which will prompt the user to authenticate
 * again via Digest authentication.
 * <p>
 * Note there are limitations to Digest authentication, although it is a more
 * comprehensive and secure solution than Basic authentication. Please see RFC 2617
 * section 4 for a full discussion on the advantages of Digest authentication over Basic
 * authentication, including commentary on the limitations that it still imposes.
 *
 * @author Ben Alex
 * @author Luke Taylor
 * @since 1.0.0
 */
public class DigestAuthenticationFilter extends GenericFilterBean
		implements MessageSourceAware {
	// ~ Static fields/initializers
	// =====================================================================================

	private static final Log logger = LogFactory.getLog(DigestAuthenticationFilter.class);

	// ~ Instance fields
	// ================================================================================================

	private AuthenticationDetailsSource<HttpServletRequest, ?> authenticationDetailsSource = new WebAuthenticationDetailsSource();
	private DigestAuthenticationEntryPoint authenticationEntryPoint;
	protected MessageSourceAccessor messages = SpringSecurityMessageSource.getAccessor();
	private UserCache userCache = new NullUserCache();
	private UserDetailsService userDetailsService;
	private boolean passwordAlreadyEncoded = false;
	private boolean createAuthenticatedToken = false;

	// ~ Methods
	// ========================================================================================================

	@Override
	public void afterPropertiesSet() {
		Assert.notNull(this.userDetailsService, "A UserDetailsService is required");
		Assert.notNull(this.authenticationEntryPoint,
				"A DigestAuthenticationEntryPoint is required");
	}

	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;

		String header = request.getHeader("Authorization");

		if (header == null || !header.startsWith("Digest ")) {
			chain.doFilter(request, response);

			return;
		}

		if (logger.isDebugEnabled()) {
			logger.debug(
					"Digest Authorization header received from user agent: " + header);
		}

		DigestData digestAuth = new DigestData(header);

		try {
			digestAuth.validateAndDecode(this.authenticationEntryPoint.getKey(),
					this.authenticationEntryPoint.getRealmName());
		}
		catch (BadCredentialsException e) {
			fail(request, response, e);

			return;
		}

		// Lookup password for presented username
		// NB: DAO-provided password MUST be clear text - not encoded/salted
		// (unless this instance's passwordAlreadyEncoded property is 'false')
		boolean cacheWasUsed = true;
		UserDetails user = this.userCache.getUserFromCache(digestAuth.getUsername());
		String serverDigestMd5;

		try {
			if (user == null) {
				cacheWasUsed = false;
				user = this.userDetailsService
						.loadUserByUsername(digestAuth.getUsername());

				if (user == null) {
					throw new AuthenticationServiceException(
							"AuthenticationDao returned null, which is an interface contract violation");
				}

				this.userCache.putUserInCache(user);
			}

			serverDigestMd5 = digestAuth.calculateServerDigest(user.getPassword(),
					request.getMethod());

			// If digest is incorrect, try refreshing from backend and recomputing
			if (!serverDigestMd5.equals(digestAuth.getResponse()) && cacheWasUsed) {
				if (logger.isDebugEnabled()) {
					logger.debug(
							"Digest comparison failure; trying to refresh user from DAO in case password had changed");
				}

				user = this.userDetailsService
						.loadUserByUsername(digestAuth.getUsername());
				this.userCache.putUserInCache(user);
				serverDigestMd5 = digestAuth.calculateServerDigest(user.getPassword(),
						request.getMethod());
			}

		}
		catch (UsernameNotFoundException notFound) {
			fail(request, response,
					new BadCredentialsException(this.messages.getMessage(
							"DigestAuthenticationFilter.usernameNotFound",
							new Object[] { digestAuth.getUsername() },
							"Username {0} not found")));

			return;
		}

		// If digest is still incorrect, definitely reject authentication attempt
		if (!serverDigestMd5.equals(digestAuth.getResponse())) {
			if (logger.isDebugEnabled()) {
				logger.debug("Expected response: '" + serverDigestMd5
						+ "' but received: '" + digestAuth.getResponse()
						+ "'; is AuthenticationDao returning clear text passwords?");
			}

			fail(request, response,
					new BadCredentialsException(this.messages.getMessage(
							"DigestAuthenticationFilter.incorrectResponse",
							"Incorrect response")));
			return;
		}

		// To get this far, the digest must have been valid
		// Check the nonce has not expired
		// We do this last so we can direct the user agent its nonce is stale
		// but the request was otherwise appearing to be valid
		if (digestAuth.isNonceExpired()) {
			fail(request, response,
					new NonceExpiredException(this.messages.getMessage(
							"DigestAuthenticationFilter.nonceExpired",
							"Nonce has expired/timed out")));

			return;
		}

		if (logger.isDebugEnabled()) {
			logger.debug("Authentication success for user: '" + digestAuth.getUsername()
					+ "' with response: '" + digestAuth.getResponse() + "'");
		}

		Authentication authentication = createSuccessfulAuthentication(request, user);
		SecurityContext context = SecurityContextHolder.createEmptyContext();
		context.setAuthentication(authentication);
		SecurityContextHolder.setContext(context);

		chain.doFilter(request, response);
	}

	private Authentication createSuccessfulAuthentication(HttpServletRequest request,
			UserDetails user) {
		UsernamePasswordAuthenticationToken authRequest;
		if (this.createAuthenticatedToken) {
			authRequest = new UsernamePasswordAuthenticationToken(user,
					user.getPassword(), user.getAuthorities());
		}
		else {
			authRequest = new UsernamePasswordAuthenticationToken(user,
					user.getPassword());
		}

		authRequest.setDetails(this.authenticationDetailsSource.buildDetails(request));

		return authRequest;
	}

	private void fail(HttpServletRequest request, HttpServletResponse response,
			AuthenticationException failed) throws IOException, ServletException {
		SecurityContextHolder.getContext().setAuthentication(null);

		if (logger.isDebugEnabled()) {
			logger.debug(failed);
		}

		this.authenticationEntryPoint.commence(request, response, failed);
	}

	protected final DigestAuthenticationEntryPoint getAuthenticationEntryPoint() {
		return this.authenticationEntryPoint;
	}

	public UserCache getUserCache() {
		return this.userCache;
	}

	public UserDetailsService getUserDetailsService() {
		return this.userDetailsService;
	}

	public void setAuthenticationDetailsSource(
			AuthenticationDetailsSource<HttpServletRequest, ?> authenticationDetailsSource) {
		Assert.notNull(authenticationDetailsSource,
				"AuthenticationDetailsSource required");
		this.authenticationDetailsSource = authenticationDetailsSource;
	}

	public void setAuthenticationEntryPoint(
			DigestAuthenticationEntryPoint authenticationEntryPoint) {
		this.authenticationEntryPoint = authenticationEntryPoint;
	}

	public void setMessageSource(MessageSource messageSource) {
		this.messages = new MessageSourceAccessor(messageSource);
	}

	public void setPasswordAlreadyEncoded(boolean passwordAlreadyEncoded) {
		this.passwordAlreadyEncoded = passwordAlreadyEncoded;
	}

	public void setUserCache(UserCache userCache) {
		this.userCache = userCache;
	}

	public void setUserDetailsService(UserDetailsService userDetailsService) {
		this.userDetailsService = userDetailsService;
	}

	/**
	 * If you set this property, the Authentication object, which is created after the
	 * successful digest authentication will be marked as <b>authenticated</b> and filled
	 * with the authorities loaded by the UserDetailsService. It therefore will not be
	 * re-authenticated by your AuthenticationProvider. This means, that only the password
	 * of the user is checked, but not the flags like isEnabled() or
	 * isAccountNonExpired(). You will save some time by enabling this flag, as otherwise
	 * your UserDetailsService will be called twice. A more secure option would be to
	 * introduce a cache around your UserDetailsService, but if you don't use these flags,
	 * you can also safely enable this option.
	 *
	 * @param createAuthenticatedToken default is false
	 */
	public void setCreateAuthenticatedToken(boolean createAuthenticatedToken) {
		this.createAuthenticatedToken = createAuthenticatedToken;
	}

	private class DigestData {
		private final String username;
		private final String realm;
		private final String nonce;
		private final String uri;
		private final String response;
		private final String qop;
		private final String nc;
		private final String cnonce;
		private final String section212response;
		private long nonceExpiryTime;

		DigestData(String header) {
			this.section212response = header.substring(7);
			String[] headerEntries = DigestAuthUtils
					.splitIgnoringQuotes(this.section212response, ',');
			Map<String, String> headerMap = DigestAuthUtils
					.splitEachArrayElementAndCreateMap(headerEntries, "=", "\"");

			this.username = headerMap.get("username");
			this.realm = headerMap.get("realm");
			this.nonce = headerMap.get("nonce");
			this.uri = headerMap.get("uri");
			this.response = headerMap.get("response");
			this.qop = headerMap.get("qop"); // RFC 2617 extension
			this.nc = headerMap.get("nc"); // RFC 2617 extension
			this.cnonce = headerMap.get("cnonce"); // RFC 2617 extension

			if (logger.isDebugEnabled()) {
				logger.debug("Extracted username: '" + this.username + "'; realm: '"
						+ this.realm + "'; nonce: '" + this.nonce + "'; uri: '" + this.uri
						+ "'; response: '" + this.response + "'");
			}
		}

		void validateAndDecode(String entryPointKey, String expectedRealm)
				throws BadCredentialsException {
			// Check all required parameters were supplied (ie RFC 2069)
			if ((this.username == null) || (this.realm == null) || (this.nonce == null)
					|| (this.uri == null) || (this.response == null)) {
				throw new BadCredentialsException(DigestAuthenticationFilter.this.messages
						.getMessage("DigestAuthenticationFilter.missingMandatory",
								new Object[] { this.section212response },
								"Missing mandatory digest value; received header {0}"));
			}
			// Check all required parameters for an "auth" qop were supplied (ie RFC 2617)
			if ("auth".equals(this.qop)) {
				if ((this.nc == null) || (this.cnonce == null)) {
					if (logger.isDebugEnabled()) {
						logger.debug("extracted nc: '" + this.nc + "'; cnonce: '"
								+ this.cnonce + "'");
					}

					throw new BadCredentialsException(
							DigestAuthenticationFilter.this.messages.getMessage(
									"DigestAuthenticationFilter.missingAuth",
									new Object[] { this.section212response },
									"Missing mandatory digest value; received header {0}"));
				}
			}

			// Check realm name equals what we expected
			if (!expectedRealm.equals(this.realm)) {
				throw new BadCredentialsException(DigestAuthenticationFilter.this.messages
						.getMessage("DigestAuthenticationFilter.incorrectRealm",
								new Object[] { this.realm, expectedRealm },
								"Response realm name '{0}' does not match system realm name of '{1}'"));
			}

			// Check nonce was Base64 encoded (as sent by DigestAuthenticationEntryPoint)
			if (!Base64.isBase64(this.nonce.getBytes())) {
				throw new BadCredentialsException(DigestAuthenticationFilter.this.messages
						.getMessage("DigestAuthenticationFilter.nonceEncoding",
								new Object[] { this.nonce },
								"Nonce is not encoded in Base64; received nonce {0}"));
			}

			// Decode nonce from Base64
			// format of nonce is:
			// base64(expirationTime + ":" + md5Hex(expirationTime + ":" + key))
			String nonceAsPlainText = new String(Base64.decode(this.nonce.getBytes()));
			String[] nonceTokens = StringUtils
					.delimitedListToStringArray(nonceAsPlainText, ":");

			if (nonceTokens.length != 2) {
				throw new BadCredentialsException(DigestAuthenticationFilter.this.messages
						.getMessage("DigestAuthenticationFilter.nonceNotTwoTokens",
								new Object[] { nonceAsPlainText },
								"Nonce should have yielded two tokens but was {0}"));
			}

			// Extract expiry time from nonce

			try {
				this.nonceExpiryTime = new Long(nonceTokens[0]).longValue();
			}
			catch (NumberFormatException nfe) {
				throw new BadCredentialsException(DigestAuthenticationFilter.this.messages
						.getMessage("DigestAuthenticationFilter.nonceNotNumeric",
								new Object[] { nonceAsPlainText },
								"Nonce token should have yielded a numeric first token, but was {0}"));
			}

			// Check signature of nonce matches this expiry time
			String expectedNonceSignature = DigestAuthUtils
					.md5Hex(this.nonceExpiryTime + ":" + entryPointKey);

			if (!expectedNonceSignature.equals(nonceTokens[1])) {
				new BadCredentialsException(DigestAuthenticationFilter.this.messages
						.getMessage("DigestAuthenticationFilter.nonceCompromised",
								new Object[] { nonceAsPlainText },
								"Nonce token compromised {0}"));
			}
		}

		String calculateServerDigest(String password, String httpMethod) {
			// Compute the expected response-digest (will be in hex form)

			// Don't catch IllegalArgumentException (already checked validity)
			return DigestAuthUtils.generateDigest(
					DigestAuthenticationFilter.this.passwordAlreadyEncoded, this.username,
					this.realm, password, httpMethod, this.uri, this.qop, this.nonce,
					this.nc, this.cnonce);
		}

		boolean isNonceExpired() {
			long now = System.currentTimeMillis();
			return this.nonceExpiryTime < now;
		}

		String getUsername() {
			return this.username;
		}

		String getResponse() {
			return this.response;
		}
	}
}
