缘起

标准的RABC, 权限需要支持动态配置，spring security默认是在代码里约定好权限，真实的业务场景通常需要可以支持动态配置角色访问权限，即在运行时去配置url对应的访问角色。

基于spring security，如何实现这个需求呢？

最简单的方法就是自定义一个Filter去完成权限判断，但这脱离了spring security框架，如何基于spring security优雅的实现呢？

spring security 授权回顾

spring security 通过FilterChainProxy作为注册到web的filter，FilterChainProxy里面一次包含了内置的多个过滤器，我们首先需要了解spring security内置的各种filter：

Alias Filter Class Namespace Element or Attribute CHANNEL_FILTER ChannelProcessingFilter http/intercept-url@requires-channel SECURITY_CONTEXT_FILTER SecurityContextPersistenceFilter http CONCURRENT_SESSION_FILTER ConcurrentSessionFilter session-management/concurrency-control HEADERS_FILTER HeaderWriterFilter http/headers CSRF_FILTER CsrfFilter http/csrf LOGOUT_FILTER LogoutFilter http/logout X509_FILTER X509AuthenticationFilter http/x509 PRE_AUTH_FILTER AbstractPreAuthenticatedProcessingFilter Subclasses N/A CAS_FILTER CasAuthenticationFilter N/A FORM_LOGIN_FILTER UsernamePasswordAuthenticationFilter http/form-login BASIC_AUTH_FILTER BasicAuthenticationFilter http/http-basic SERVLET_API_SUPPORT_FILTER SecurityContextHolderAwareRequestFilter http/@servlet-api-provision JAAS_API_SUPPORT_FILTER JaasApiIntegrationFilter http/@jaas-api-provision REMEMBER_ME_FILTER RememberMeAuthenticationFilter http/remember-me ANONYMOUS_FILTER AnonymousAuthenticationFilter http/anonymous SESSION_MANAGEMENT_FILTER SessionManagementFilter session-management EXCEPTION_TRANSLATION_FILTER ExceptionTranslationFilter http FILTER_SECURITY_INTERCEPTOR FilterSecurityInterceptor http SWITCH_USER_FILTER SwitchUserFilter N/A

最重要的是FilterSecurityInterceptor，该过滤器实现了主要的鉴权逻辑，最核心的代码在这里：

protected InterceptorStatusToken beforeInvocation(Object object) { // 获取访问URL所需权限 Collection<ConfigAttribute> attributes = this.obtainSecurityMetadataSource() .getAttributes(object); Authentication authenticated = authenticateIfRequired(); // 通过accessDecisionManager鉴权 try { this.accessDecisionManager.decide(authenticated, object, attributes); } catch (AccessDeniedException accessDeniedException) { publishEvent(new AuthorizationFailureEvent(object, attributes, authenticated, accessDeniedException)); throw accessDeniedException; } if (debug) { logger.debug("Authorization successful"); } if (publishAuthorizationSuccess) { publishEvent(new AuthorizedEvent(object, attributes, authenticated)); } // Attempt to run as a different user Authentication runAs = this.runAsManager.buildRunAs(authenticated, object, attributes); if (runAs == null) { if (debug) { logger.debug("RunAsManager did not change Authentication object"); } // no further work post-invocation return new InterceptorStatusToken(SecurityContextHolder.getContext(), false, attributes, object); } else { if (debug) { logger.debug("Switching to RunAs Authentication: " + runAs); } SecurityContext origCtx = SecurityContextHolder.getContext(); SecurityContextHolder.setContext(SecurityContextHolder.createEmptyContext()); SecurityContextHolder.getContext().setAuthentication(runAs); // need to revert to token.Authenticated post-invocation return new InterceptorStatusToken(origCtx, true, attributes, object); } }

从上面可以看出，要实现动态鉴权，可以从两方面着手：

• 自定义SecurityMetadataSource，实现从数据库加载ConfigAttribute
• 另外就是可以自定义accessDecisionManager，官方的UnanimousBased其实足够使用，并且他是基于AccessDecisionVoter来实现权限认证的，因此我们只需要自定义一个AccessDecisionVoter就可以了

下面来看分别如何实现。

自定义AccessDecisionManager

官方的三个AccessDecisionManager都是基于AccessDecisionVoter来实现权限认证的，因此我们只需要自定义一个AccessDecisionVoter就可以了。

自定义主要是实现AccessDecisionVoter接口，我们可以仿照官方的RoleVoter实现一个：

public class RoleBasedVoter implements AccessDecisionVoter<Object> { @Override public boolean supports(ConfigAttribute attribute) { return true; } @Override public int vote(Authentication authentication, Object object, Collection<ConfigAttribute> attributes) { if(authentication == null) { return ACCESS_DENIED; } int result = ACCESS_ABSTAIN; Collection<? extends GrantedAuthority> authorities = extractAuthorities(authentication); for (ConfigAttribute attribute : attributes) { if(attribute.getAttribute()==null){ continue; } if (this.supports(attribute)) { result = ACCESS_DENIED; // Attempt to find a matching granted authority for (GrantedAuthority authority : authorities) { if (attribute.getAttribute().equals(authority.getAuthority())) { return ACCESS_GRANTED; } } } } return result; } Collection<? extends GrantedAuthority> extractAuthorities( Authentication authentication) { return authentication.getAuthorities(); } @Override public boolean supports(Class clazz) { return true; }}

如何加入动态权限呢？

vote(Authentication authentication, Object object, Collection<ConfigAttribute> attributes)里的Object object的类型是FilterInvocation，可以通过getRequestUrl获取当前请求的URL:

FilterInvocation fi = (FilterInvocation) object; String url = fi.getRequestUrl();

因此这里扩展空间就大了，可以从DB动态加载，然后判断URL的ConfigAttribute就可以了。

如何使用这个RoleBasedVoter呢？在configure里使用accessDecisionManager方法自定义，我们还是使用官方的UnanimousBased，然后将自定义的RoleBasedVoter加入即可。

@EnableWebSecurity@EnableGlobalMethodSecurity(prePostEnabled = true, securedEnabled = true)public class SecurityConfiguration extends WebSecurityConfigurerAdapter { @Override protected void configure(HttpSecurity http) throws Exception { http .addFilterBefore(corsFilter, UsernamePasswordAuthenticationFilter.class) .exceptionHandling() .authenticationEntryPoint(problemSupport) .accessDeniedHandler(problemSupport) .and() .csrf() .disable() .headers() .frameOptions() .disable() .and() .sessionManagement() .sessionCreationPolicy(SessionCreationPolicy.STATELESS) .and() .authorizeRequests() // 自定义accessDecisionManager .accessDecisionManager(accessDecisionManager()) .and() .apply(securityConfigurerAdapter()); } @Bean public AccessDecisionManager accessDecisionManager() { List<AccessDecisionVoter<? extends Object>> decisionVoters = Arrays.asList( new WebExpressionVoter(), // new RoleVoter(), new RoleBasedVoter(), new AuthenticatedVoter()); return new UnanimousBased(decisionVoters); }

自定义SecurityMetadataSource

自定义FilterInvocationSecurityMetadataSource只要实现接口即可，在接口里从DB动态加载规则。

为了复用代码里的定义，我们可以将代码里生成的SecurityMetadataSource带上，在构造函数里传入默认的FilterInvocationSecurityMetadataSource。

public class AppFilterInvocationSecurityMetadataSource implements org.springframework.security.web.access.intercept.FilterInvocationSecurityMetadataSource { private FilterInvocationSecurityMetadataSource superMetadataSource; @Override public Collection<ConfigAttribute> getAllConfigAttributes() { return null; } public AppFilterInvocationSecurityMetadataSource(FilterInvocationSecurityMetadataSource expressionBasedFilterInvocationSecurityMetadataSource){ this.superMetadataSource = expressionBasedFilterInvocationSecurityMetadataSource; // TODO 从数据库加载权限配置 } private final AntPathMatcher antPathMatcher = new AntPathMatcher(); // 这里的需要从DB加载 private final Map<String,String> urlRoleMap = new HashMap<String,String>(){{ put("/open/**","ROLE_ANONYMOUS"); put("/health","ROLE_ANONYMOUS"); put("/restart","ROLE_ADMIN"); put("/demo","ROLE_USER"); }}; @Override public Collection<ConfigAttribute> getAttributes(Object object) throws IllegalArgumentException { FilterInvocation fi = (FilterInvocation) object; String url = fi.getRequestUrl(); for(Map.Entry<String,String> entry:urlRoleMap.entrySet()){ if(antPathMatcher.match(entry.getKey(),url)){ return SecurityConfig.createList(entry.getValue()); } } // 返回代码定义的默认配置 return superMetadataSource.getAttributes(object); } @Override public boolean supports(Class<?> clazz) { return FilterInvocation.class.isAssignableFrom(clazz); }}

怎么使用？和accessDecisionManager不一样，ExpressionUrlAuthorizationConfigurer 并没有提供set方法设置FilterSecurityInterceptor的FilterInvocationSecurityMetadataSource，how to do?

发现一个扩展方法withObjectPostProcessor，通过该方法自定义一个处理FilterSecurityInterceptor类型的ObjectPostProcessor就可以修改FilterSecurityInterceptor。

@EnableWebSecurity@EnableGlobalMethodSecurity(prePostEnabled = true, securedEnabled = true)public class SecurityConfiguration extends WebSecurityConfigurerAdapter { @Override protected void configure(HttpSecurity http) throws Exception { http .addFilterBefore(corsFilter, UsernamePasswordAuthenticationFilter.class) .exceptionHandling() .authenticationEntryPoint(problemSupport) .accessDeniedHandler(problemSupport) .and() .csrf() .disable() .headers() .frameOptions() .disable() .and() .sessionManagement() .sessionCreationPolicy(SessionCreationPolicy.STATELESS) .and() .authorizeRequests() // 自定义FilterInvocationSecurityMetadataSource .withObjectPostProcessor(new ObjectPostProcessor<FilterSecurityInterceptor>() { @Override public <O extends FilterSecurityInterceptor> O postProcess( O fsi) { fsi.setSecurityMetadataSource(mySecurityMetadataSource(fsi.getSecurityMetadataSource())); return fsi; } }) .and() .apply(securityConfigurerAdapter()); } @Bean public AppFilterInvocationSecurityMetadataSource mySecurityMetadataSource(FilterInvocationSecurityMetadataSource filterInvocationSecurityMetadataSource) { AppFilterInvocationSecurityMetadataSource securityMetadataSource = new AppFilterInvocationSecurityMetadataSource(filterInvocationSecurityMetadataSource); return securityMetadataSource;}

小结

本文介绍了两种基于spring security实现动态权限的方法，一是自定义accessDecisionManager，二是自定义FilterInvocationSecurityMetadataSource。实际项目里可以根据需要灵活选择。

延伸阅读:

Spring Security 架构与源码分析

总结

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