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