为了更好的描述问题,我们拿使用表单认证的网站举例,简化后的认证过程分为7步:
用户访问网站,打开了一个链接(origin url)。
请求发送给服务器,服务器判断用户请求了受保护的资源。
由于用户没有登录,服务器重定向到登录页面
填写表单,点击登录
浏览器将用户名密码以表单形式发送给服务器
服务器验证用户名密码。成功,进入到下一步。否则要求用户重新认证(第三步)
服务器对用户拥有的权限(角色)判定: 有权限,重定向到origin url; 权限不足,返回状态码403("forbidden").
从第3步,我们可以知道,用户的请求被中断了。
用户登录成功后(第7步),会被重定向到origin url,spring security通过使用缓存的request,使得被中断的请求能够继续执行。
用户登录成功后,页面重定向到origin url。浏览器发出的请求优先被拦截器RequestCacheAwareFilter拦截,RequestCacheAwareFilter通过其持有的RequestCache对象实现request的恢复。
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // request匹配,则取出,该操作同时会将缓存的request从session中删除 HttpServletRequest wrappedSavedRequest = requestCache.getMatchingRequest( (HttpServletRequest) request, (HttpServletResponse) response); // 优先使用缓存的request chain.doFilter(wrappedSavedRequest == null ? request : wrappedSavedRequest, response); }
首先,我们需要了解下RequestCache以及ExceptionTranslationFilter。
RequestCache
RequestCache接口声明了缓存与恢复操作。默认实现类是 HttpSessionRequestCache
。HttpSessionRequestCache的实现比较简单,这里只列出接口的声明:
public interface RequestCache { // 将request缓存到session中 void saveRequest(HttpServletRequest request, HttpServletResponse response); // 从session中取request SavedRequest getRequest(HttpServletRequest request, HttpServletResponse response); // 获得与当前request匹配的缓存,并将匹配的request从session中删除 HttpServletRequest getMatchingRequest(HttpServletRequest request, HttpServletResponse response); // 删除缓存的request void removeRequest(HttpServletRequest request, HttpServletResponse response); }
ExceptionTranslationFilter
ExceptionTranslationFilter 是Spring Security的核心filter之一,用来处理AuthenticationException和AccessDeniedException两种异常。
在我们的例子中,AuthenticationException指的是未登录状态下访问受保护资源,AccessDeniedException指的是登陆了但是由于权限不足(比如普通用户访问管理员界面)。
ExceptionTranslationFilter 持有两个处理类,分别是AuthenticationEntryPoint和AccessDeniedHandler。
ExceptionTranslationFilter 对异常的处理是通过这两个处理类实现的,处理规则很简单:
规则1. 如果异常是 AuthenticationException,使用 AuthenticationEntryPoint 处理
规则2. 如果异常是 AccessDeniedException 且用户是匿名用户,使用 AuthenticationEntryPoint 处理
规则3. 如果异常是 AccessDeniedException 且用户不是匿名用户,如果否则交给 AccessDeniedHandler 处理。
对应以下代码
private void handleSpringSecurityException(HttpServletRequest request, HttpServletResponse response, FilterChain chain, RuntimeException exception) throws IOException, ServletException { if (exception instanceof AuthenticationException) { logger.debug( "Authentication exception occurred; redirecting to authentication entry point", exception); sendStartAuthentication(request, response, chain, (AuthenticationException) exception); } else if (exception instanceof AccessDeniedException) { if (authenticationTrustResolver.isAnonymous(SecurityContextHolder .getContext().getAuthentication())) { logger.debug( "Access is denied (user is anonymous); redirecting to authentication entry point", exception); sendStartAuthentication( request, response, chain, new InsufficientAuthenticationException( "Full authentication is required to access this resource")); } else { logger.debug( "Access is denied (user is not anonymous); delegating to AccessDeniedHandler", exception); accessDeniedHandler.handle(request, response, (AccessDeniedException) exception); } } }
AccessDeniedHandler 默认实现是 AccessDeniedHandlerImpl。该类对异常的处理是返回403错误码。
public void handle(HttpServletRequest request, HttpServletResponse response, AccessDeniedException accessDeniedException) throws IOException, ServletException { if (!response.isCommitted()) { if (errorPage != null) { // 定义了errorPage // errorPage中可以操作该异常 request.setAttribute(WebAttributes.ACCESS_DENIED_403, accessDeniedException); // 设置403状态码 response.setStatus(HttpServletResponse.SC_FORBIDDEN); // 转发到errorPage RequestDispatcher dispatcher = request.getRequestDispatcher(errorPage); dispatcher.forward(request, response); } else { // 没有定义errorPage,则返回403状态码(Forbidden),以及错误信息 response.sendError(HttpServletResponse.SC_FORBIDDEN, accessDeniedException.getMessage()); } } }
AuthenticationEntryPoint 默认实现是 LoginUrlAuthenticationEntryPoint, 该类的处理是转发或重定向到登录页面
public void commence(HttpServletRequest request, HttpServletResponse response, AuthenticationException authException) throws IOException, ServletException { String redirectUrl = null; if (useForward) { if (forceHttps && "http".equals(request.getScheme())) { // First redirect the current request to HTTPS. // When that request is received, the forward to the login page will be // used. redirectUrl = buildHttpsRedirectUrlForRequest(request); } if (redirectUrl == null) { String loginForm = determineUrlToUseForThisRequest(request, response, authException); if (logger.isDebugEnabled()) { logger.debug("Server side forward to: " + loginForm); } RequestDispatcher dispatcher = request.getRequestDispatcher(loginForm); // 转发 dispatcher.forward(request, response); return; } } else { // redirect to login page. Use https if forceHttps true redirectUrl = buildRedirectUrlToLoginPage(request, response, authException); } // 重定向 redirectStrategy.sendRedirect(request, response, redirectUrl); }
了解完这些,回到我们的例子。
第3步时,用户未登录的情况下访问受保护资源,ExceptionTranslationFilter会捕获到AuthenticationException异常(规则1)。页面需要跳转,ExceptionTranslationFilter在跳转前使用requestCache缓存request。
protected void sendStartAuthentication(HttpServletRequest request, HttpServletResponse response, FilterChain chain, AuthenticationException reason) throws ServletException, IOException { // SEC-112: Clear the SecurityContextHolder's Authentication, as the // existing Authentication is no longer considered valid SecurityContextHolder.getContext().setAuthentication(null); // 缓存 request requestCache.saveRequest(request, response); logger.debug("Calling Authentication entry point."); authenticationEntryPoint.commence(request, response, reason); }
在开发过程中,如果不理解Spring Security如何缓存request,可能会踩一些坑。
举个简单例子,如果网站认证是信息存放在header中。第一次请求受保护资源时,请求头中不包含认证信息 ,验证失败,该请求会被缓存,之后即使用户填写了信息,也会因为request被恢复导致信息丢失从而认证失败(问题描述可以参见 这里 。
最简单的方案当然是不缓存request。
spring security 提供了NullRequestCache, 该类实现了 RequestCache 接口,但是没有任何操作。
public class NullRequestCache implements RequestCache { public SavedRequest getRequest(HttpServletRequest request, HttpServletResponse response) { return null; } public void removeRequest(HttpServletRequest request, HttpServletResponse response) { } public void saveRequest(HttpServletRequest request, HttpServletResponse response) { } public HttpServletRequest getMatchingRequest(HttpServletRequest request, HttpServletResponse response) { return null; } }
配置requestCache,使用如下代码即可:
http.requestCache().requestCache(new NullRequestCache());
默认情况下,三种request不会被缓存。
/favicon.ico
结尾 content-type
值为 application/json
X-Requested-With
值为 XMLHttpRequest
可以参见:RequestCacheConfigurer类中的私有方法createDefaultSavedRequestMatcher。
附上实例代码: https://coding.net/u/tanhe123/p/SpringSecurityRequestCache