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。
总结
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