Spring Security 源码解析(一)

上篇 Spring Security基本配置已讲述了Spring Security最简单的配置，本篇将开始分析其基本原理

在上篇中可以看到，在访问 http://localhost:18081/user 时，直接跳转到登录页。那Security是怎么做的呢？本篇主要讲述跳转到登录页前的处理

首先来看一张时序图：

通过上图可以看到，请求顺序为AbstractAuthenticationProcessingFilter -> AnonymousAuthenticationFilter -> ExceptionTranslationFilter -> FilterSecurityInterceptor

AbstractAuthenticationProcessingFilter

请求先进入 AbstractAuthenticationProcessingFilter 的doFilter()方法。判断当前filter是否可以处理当前请求(也就是是否包含用户名密码信息)，如果是，则调用其子类 UsernamePasswordAuthenticationFilter.attemptAuthentication() 方法进行验证(第一次请求时，没有用户名密码，是不会调用子类的)

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
　　　　
        //判断当前的filter是否可以处理当前请求，不可以的话则交给下一个filter处理
        if (!requiresAuthentication(request, response)) {
            chain.doFilter(request, response);

            return;
        }

        if (logger.isDebugEnabled()) {
            logger.debug("Request is to process authentication");
        }

        Authentication authResult;

        try {
            //抽象方法由子类UsernamePasswordAuthenticationFilter实现
            authResult = attemptAuthentication(request, response);
            if (authResult == null) {
                // return immediately as subclass has indicated that it hasn't completed
                // authentication
                return;
            }
            //认证成功后，处理一些与session相关的方法
            sessionStrategy.onAuthentication(authResult, request, response);
        }
        catch (InternalAuthenticationServiceException failed) {
            logger.error(
                    "An internal error occurred while trying to authenticate the user.",
                    failed);
            //认证失败后的的一些操作
            unsuccessfulAuthentication(request, response, failed);

            return;
        }
        catch (AuthenticationException failed) {
            // Authentication failed
            unsuccessfulAuthentication(request, response, failed);

            return;
        }

        // Authentication success
        if (continueChainBeforeSuccessfulAuthentication) {
            chain.doFilter(request, response);
        }
        //认证成功后的相关回调方法，主要将当前的认证放到SecurityContextHolder中
        successfulAuthentication(request, response, chain, authResult);
    }

认证成功后的回调方法：

protected void successfulAuthentication(HttpServletRequest request,
            HttpServletResponse response, FilterChain chain, Authentication authResult)
            throws IOException, ServletException {

        if (logger.isDebugEnabled()) {
            logger.debug("Authentication success. Updating SecurityContextHolder to contain: "
                    + authResult);
        }

        //将认证结果保存到SecurityContextHolder中
        SecurityContextHolder.getContext().setAuthentication(authResult);

        rememberMeServices.loginSuccess(request, response, authResult);

        // Fire event
        if (this.eventPublisher != null) {
            eventPublisher.publishEvent(new InteractiveAuthenticationSuccessEvent(
                    authResult, this.getClass()));
        }

        //调用其它可扩展的 handlers 继续处理该认证成功以后的回调事件
        //实现AuthenticationSuccessHandler接口即可
        successHandler.onAuthenticationSuccess(request, response, authResult);
    }

认证失败后的回调方法：

protected void unsuccessfulAuthentication(HttpServletRequest request,
            HttpServletResponse response, AuthenticationException failed)
            throws IOException, ServletException {
        
        //清除SecurityContextHolder的中数据
        SecurityContextHolder.clearContext();

        if (logger.isDebugEnabled()) {
            logger.debug("Authentication request failed: " + failed.toString(), failed);
            logger.debug("Updated SecurityContextHolder to contain null Authentication");
            logger.debug("Delegating to authentication failure handler " + failureHandler);
        }

        rememberMeServices.loginFail(request, response);

        //调用其它可扩展的 handlers 处理该认证失败以后的回调事件
        //实现 AuthenticationFailureHandler 接口即可
        failureHandler.onAuthenticationFailure(request, response, failed);
    

关于自定义 handlers ，可参考 Spring Security认证配置(三)

UsernamePasswordAuthenticationFilter

UsernamePasswordAuthenticationFilter本身不是过滤器，而是继承了AbstractAuthenticationProcessingFilter才拥有过滤器的性能，其主要是验证用户名密码。

public Authentication attemptAuthentication(HttpServletRequest request,
            HttpServletResponse response) throws AuthenticationException {
        
        //认证请求的方法必须为POST
        if (postOnly && !request.getMethod().equals("POST")) {
            throw new AuthenticationServiceException(
                    "Authentication method not supported: " + request.getMethod());
        }

        //从request中获取 username 和 password
        String username = obtainUsername(request);
        String password = obtainPassword(request);

        if (username == null) {
            username = "";
        }

        if (password == null) {
            password = "";
        }

        username = username.trim();

        //封装Authenticaiton的实现类UsernamePasswordAuthenticationToken
        //传入用户名和密码，并将是否已经认证设为false
        UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(
                username, password);

        //设置UsernamePasswordAuthenticationToken中的详细信息。如remoteAddress、sessionId
        // Allow subclasses to set the "details" property
        setDetails(request, authRequest);

        //调用 AuthenticationManager 的实现类 ProviderManager 进行验证
        return this.getAuthenticationManager().authenticate(authRequest);
    }

验证的过程，可以参考AuthenticationManager、ProviderManager

ExceptionTranslationFilter

ExceptionTranslationFilter是异常处理过滤器，该过滤器用来处理在系统认证授权过程中抛出的异常(也就是FilterSecurityInterceptor抛出来的)，主要是处理

AccessDeniedException、AuthenticationException

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

        try {
            chain.doFilter(request, response);

            logger.debug("Chain processed normally");
        }
        catch (IOException ex) {
            throw ex;
        }
        catch (Exception ex) {
            //判断是不是AuthenticationException
            // Try to extract a SpringSecurityException from the stacktrace
            Throwable[] causeChain = throwableAnalyzer.determineCauseChain(ex);
            RuntimeException ase = (AuthenticationException) throwableAnalyzer
                    .getFirstThrowableOfType(AuthenticationException.class, causeChain);

            if (ase == null) {
                //判断是不是AccessDeniedException
                ase = (AccessDeniedException) throwableAnalyzer.getFirstThrowableOfType(
                        AccessDeniedException.class, causeChain);
            }

            if (ase != null) {
                //异常处理。包括缓存当前请求，跳转到登录页
                handleSpringSecurityException(request, response, chain, ase);
            }
            else {
                // Rethrow ServletExceptions and RuntimeExceptions as-is
                if (ex instanceof ServletException) {
                    throw (ServletException) ex;
                }
                else if (ex instanceof RuntimeException) {
                    throw (RuntimeException) ex;
                }

                // Wrap other Exceptions. This shouldn't actually happen
                // as we've already covered all the possibilities for doFilter
                throw new RuntimeException(ex);
            }
        }
    }

在 handleSpringSecurityException 方法中，有一段：

　　　　　　　Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
            //判断当前authentication是不是AnonymousAuthenticationToken(RememberMeAuthenticationToken)或者其子类
            if (authenticationTrustResolver.isAnonymous(authentication) || authenticationTrustResolver.isRememberMe(authentication)) {
                logger.debug(
                        "Access is denied (user is " + (authenticationTrustResolver.isAnonymous(authentication) ? "anonymous" : "not fully authenticated") + "); redirecting to authentication entry point",
                        exception);
                
                sendStartAuthentication(
                        request,
                        response,
                        chain,
                        new InsufficientAuthenticationException(
                                "Full authentication is required to access this resource"));
            }

其中sendStartAuthentication方法：

protected void sendStartAuthentication(HttpServletRequest request,
            HttpServletResponse response, FilterChain chain,
            AuthenticationException reason) throws ServletException, IOException {
　　　　 //清空SecurityContext
        SecurityContextHolder.getContext().setAuthentication(null);
        //缓存当前请求
        requestCache.saveRequest(request, response);
        logger.debug("Calling Authentication entry point.");
        //调用AuthenticationEntryPoint的实现类LoginUrlAuthenticationEntryPoint(可扩展，实现AuthenticationEntryPoint即可)
        //跳转到可配置的登录页(如果不配置，则跳转到spring security默认的登录页)
        authenticationEntryPoint.commence(request, response, reason);
    }

FilterSecurityInterceptor 

此过滤器为认证授权过滤器链中最后一个过滤器，该过滤器通过之后就是真正的 /user 服务

public void invoke(FilterInvocation fi) throws IOException, ServletException {
        ......
else {
            // first time this request being called, so perform security checking
            if (fi.getRequest() != null) {
                fi.getRequest().setAttribute(FILTER_APPLIED, Boolean.TRUE);
            }
            //调用父类AbstractSecurityInterceptor.beforeInvocation方法，进行最后一次过滤
            InterceptorStatusToken token = super.beforeInvocation(fi);

            try {
                //请求真正的 /user 服务
                fi.getChain().doFilter(fi.getRequest(), fi.getResponse());
            }
            finally {
                super.finallyInvocation(token);
            }

            super.afterInvocation(token, null);
        }
    }

在beforeInvocation方法中，会调用AccessDecisionManager.decide方法来验证当前认证成功的用户是否有权限访问该资源

protected InterceptorStatusToken beforeInvocation(Object object) {
        ......

        Collection<ConfigAttribute> attributes = this.obtainSecurityMetadataSource()
                .getAttributes(object);

        ......

        Authentication authenticated = authenticateIfRequired();

        // Attempt authorization
        try {
            //授权认证
            this.accessDecisionManager.decide(authenticated, object, attributes);
        }
        catch (AccessDeniedException accessDeniedException) {
            publishEvent(new AuthorizationFailureEvent(object, attributes, authenticated,
                    accessDeniedException));

            throw accessDeniedException;
        }
    }

 上面的object和attributes是什么？调试一下：

 object为当前请求 URL:/user

 requestMap的值有两个，如下图：

可以看到，这两个值对应SecurityConfig中的配置。第一个为antMatchs返回permitAll即不需要认证，第二个为anyRequest返回authenticated即其它请求需要认证

所以 getAttributes 就是使用当前请求路径去匹配我们自定义的规则，attributes为匹配后的结果

我们继续来看最核心的授权认证：

this.accessDecisionManager.decide(authenticated, object, attributes)

此时，authenticated为匿名AnonymousAuthenticationToken，attributes为authenticated

AccessDecisionManager是如何授权的呢？

Spring Security默认使用AccessDecisionManager的子类 AffirmativeBased，通过实现decide方法来鉴定用户是否有访问对应资源(方法或URL)的权限

public void decide(Authentication authentication, Object object,
            Collection<ConfigAttribute> configAttributes) throws AccessDeniedException {
        int deny = 0;

        //调用AccessDecisionVoter进行vote(投票)
        for (AccessDecisionVoter voter : getDecisionVoters()) {
            int result = voter.vote(authentication, object, configAttributes);

            if (logger.isDebugEnabled()) {
                logger.debug("Voter: " + voter + ", returned: " + result);
            }

            switch (result) {
            //voter投票为ACCESS_GRANTED，表示同意，直接返回
            case AccessDecisionVoter.ACCESS_GRANTED:
                return;
            //voter投票为ACCESS_DENIED，表示反对，则记录一下
            case AccessDecisionVoter.ACCESS_DENIED:
                deny++;

                break;
            //voter投票为其它值，则表示弃权。都弃权也会通过
            default:
                break;
            }
        }

        //只要有一个voter投票为ACCESS_DENIED，则直接就不通过了
        if (deny > 0) {
            throw new AccessDeniedException(messages.getMessage(
                    "AbstractAccessDecisionManager.accessDenied", "Access is denied"));
        }

        // To get this far, every AccessDecisionVoter abstained
        checkAllowIfAllAbstainDecisions();
    }

第一次请求，这里将抛出AccessDeniedException。然后被ExceptionTranslationFilter捕获，跳转到授权登录认证页面