前言
现在流行的通用授权框架有apache的shiro和Spring家族的Spring Security,在涉及今天的微服务鉴权时,需要利用我们的授权框架搭建自己的鉴权服务,今天总理了Spring Security。
Spring Security 主要实现了Authentication（认证，解决who are you? ） 和 Access Control（访问控制，也就是what are you allowed to do？，也称为Authorization）。Spring Security在架构上将认证与授权分离，并提供了扩展点。
核心对象
主要代码在spring-security-core包下面。要了解Spring Security，需要先关注里面的核心对象。
SecurityContextHolder, SecurityContext 和 Authentication
SecurityContextHolder 是 SecurityContext的存放容器，默认使用ThreadLocal 存储，意味SecurityContext在相同线程中的方法都可用。
SecurityContext主要是存储应用的principal信息，在Spring Security中用Authentication 来表示。
获取principal：
Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal();if (principal instanceof UserDetails) {String username = ((UserDetails)principal).getUsername();} else {String username = principal.toString();}在Spring Security中，可以看一下Authentication定义：
public interface Authentication extends Principal, Serializable { Collection<? extends GrantedAuthority> getAuthorities(); /** * 通常是密码 */ Object getCredentials(); /** * Stores additional details about the authentication request. These might be an IP * address, certificate serial number etc. */ Object getDetails(); /** * 用来标识是否已认证，如果使用用户名和密码登录,通常是用户名 */ Object getPrincipal(); /** * 是否已认证 */ boolean isAuthenticated(); void setAuthenticated(boolean isAuthenticated) throws IllegalArgumentException;}在实际应用中，通常使用UsernamePasswordAuthenticationToken：
public abstract class AbstractAuthenticationToken implements Authentication, CredentialsContainer { }public class UsernamePasswordAuthenticationToken extends AbstractAuthenticationToken {}一个常见的认证过程通常是这样的，创建一个UsernamePasswordAuthenticationToken，然后交给authenticationManager认证（后面详细说明），认证通过则通过SecurityContextHolder存放Authentication信息。
UsernamePasswordAuthenticationToken authenticationToken = new UsernamePasswordAuthenticationToken(loginVM.getUsername(), loginVM.getPassword());Authentication authentication = this.authenticationManager.authenticate(authenticationToken);SecurityContextHolder.getContext().setAuthentication(authentication);
UserDetails与UserDetailsService
UserDetails 是Spring Security里的一个关键接口，他用来表示一个principal。
public interface UserDetails extends Serializable { /** * 用户的授权信息，可以理解为角色 */ Collection<? extends GrantedAuthority> getAuthorities(); /** * 用户密码 * * @return the password */ String getPassword(); /** * 用户名 * */ String getUsername(); boolean isAccountNonExpired(); boolean isAccountNonLocked(); boolean isCredentialsNonExpired(); boolean isEnabled();}UserDetails提供了认证所需的必要信息，在实际使用里，可以自己实现UserDetails，并增加额外的信息，比如email、mobile等信息。
在Authentication中的principal通常是用户名，我们可以通过UserDetailsService来通过principal获取UserDetails：
public interface UserDetailsService { UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;}GrantedAuthority
在UserDetails里说了，GrantedAuthority可以理解为角色，例如 ROLE_ADMINISTRATOR or ROLE_HR_SUPERVISOR。
小结
Authentication认证
AuthenticationManager
实现认证主要是通过AuthenticationManager接口，它只包含了一个方法：
public interface AuthenticationManager { Authentication authenticate(Authentication authentication) throws AuthenticationException;}authenticate()方法主要做三件事：
AuthenticationException是运行时异常,它通常由应用程序按通用方式处理，用户代码通常不用特意被捕获和处理这个异常。
AuthenticationManager的默认实现是ProviderManager，它委托一组AuthenticationProvider实例来实现认证。
AuthenticationProvider和AuthenticationManager类似，都包含authenticate，但它有一个额外的方法supports，以允许查询调用方是否支持给定Authentication类型：
public interface AuthenticationProvider { Authentication authenticate(Authentication authentication) throws AuthenticationException; boolean supports(Class<?> authentication);}ProviderManager包含一组AuthenticationProvider，执行authenticate时，遍历Providers，然后调用supports，如果支持，则执行遍历当前provider的authenticate方法，如果一个provider认证成功，则break。
public Authentication authenticate(Authentication authentication) throws AuthenticationException { Class<? extends Authentication> toTest = authentication.getClass(); AuthenticationException lastException = null; Authentication result = null; boolean debug = logger.isDebugEnabled(); for (AuthenticationProvider provider : getProviders()) { if (!provider.supports(toTest)) { continue; } if (debug) { logger.debug("Authentication attempt using " + provider.getClass().getName()); } try { result = provider.authenticate(authentication); if (result != null) { copyDetails(authentication, result); break; } } catch (AccountStatusException e) { prepareException(e, authentication); // SEC-546: Avoid polling additional providers if auth failure is due to // invalid account status throw e; } catch (InternalAuthenticationServiceException e) { prepareException(e, authentication); throw e; } catch (AuthenticationException e) { lastException = e; } } if (result == null && parent != null) { // Allow the parent to try. try { result = parent.authenticate(authentication); } catch (ProviderNotFoundException e) { // ignore as we will throw below if no other exception occurred prior to // calling parent and the parent // may throw ProviderNotFound even though a provider in the child already // handled the request } catch (AuthenticationException e) { lastException = e; } } if (result != null) { if (eraseCredentialsAfterAuthentication && (result instanceof CredentialsContainer)) { // Authentication is complete. Remove credentials and other secret data // from authentication ((CredentialsContainer) result).eraseCredentials(); } eventPublisher.publishAuthenticationSuccess(result); return result; } // Parent was null, or didn't authenticate (or throw an exception). if (lastException == null) { lastException = new ProviderNotFoundException(messages.getMessage( "ProviderManager.providerNotFound", new Object[] { toTest.getName() }, "No AuthenticationProvider found for {0}")); } prepareException(lastException, authentication); throw lastException; }从上面的代码可以看出， ProviderManager有一个可选parent，如果parent不为空，则调用parent.authenticate(authentication)
AuthenticationProvider
AuthenticationProvider有多种实现，大家最关注的通常是DaoAuthenticationProvider，继承于AbstractUserDetailsAuthenticationProvider，核心是通过UserDetails来实现认证,DaoAuthenticationProvider默认会自动加载，不用手动配。
先来看AbstractUserDetailsAuthenticationProvider，看最核心的authenticate：
public Authentication authenticate(Authentication authentication) throws AuthenticationException { // 必须是UsernamePasswordAuthenticationToken Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication, messages.getMessage( "AbstractUserDetailsAuthenticationProvider.onlySupports", "Only UsernamePasswordAuthenticationToken is supported")); // 获取用户名 String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED" : authentication.getName(); boolean cacheWasUsed = true; // 从缓存获取 UserDetails user = this.userCache.getUserFromCache(username); if (user == null) { cacheWasUsed = false; try { // retrieveUser 抽象方法，获取用户 user = retrieveUser(username, (UsernamePasswordAuthenticationToken) authentication); } catch (UsernameNotFoundException notFound) { logger.debug("User '" + username + "' not found"); if (hideUserNotFoundExceptions) { throw new BadCredentialsException(messages.getMessage( "AbstractUserDetailsAuthenticationProvider.badCredentials", "Bad credentials")); } else { throw notFound; } } Assert.notNull(user, "retrieveUser returned null - a violation of the interface contract"); } try { // 预先检查，DefaultPreAuthenticationChecks，检查用户是否被lock或者账号是否可用 preAuthenticationChecks.check(user); // 抽象方法，自定义检验 additionalAuthenticationChecks(user, (UsernamePasswordAuthenticationToken) authentication); } catch (AuthenticationException exception) { if (cacheWasUsed) { // There was a problem, so try again after checking // we're using latest data (i.e. not from the cache) cacheWasUsed = false; user = retrieveUser(username, (UsernamePasswordAuthenticationToken) authentication); preAuthenticationChecks.check(user); additionalAuthenticationChecks(user, (UsernamePasswordAuthenticationToken) authentication); } else { throw exception; } } // 后置检查 DefaultPostAuthenticationChecks，检查isCredentialsNonExpired postAuthenticationChecks.check(user); if (!cacheWasUsed) { this.userCache.putUserInCache(user); } Object principalToReturn = user; if (forcePrincipalAsString) { principalToReturn = user.getUsername(); } return createSuccessAuthentication(principalToReturn, authentication, user); }上面的检验主要基于UserDetails实现，其中获取用户和检验逻辑由具体的类去实现，默认实现是DaoAuthenticationProvider，这个类的核心是让开发者提供UserDetailsService来获取UserDetails以及 PasswordEncoder来检验密码是否有效：
private UserDetailsService userDetailsService;private PasswordEncoder passwordEncoder;
看具体的实现，retrieveUser,直接调用userDetailsService获取用户：
protected final UserDetails retrieveUser(String username, UsernamePasswordAuthenticationToken authentication) throws AuthenticationException { UserDetails loadedUser; try { loadedUser = this.getUserDetailsService().loadUserByUsername(username); } catch (UsernameNotFoundException notFound) { if (authentication.getCredentials() != null) { String presentedPassword = authentication.getCredentials().toString(); passwordEncoder.isPasswordValid(userNotFoundEncodedPassword, presentedPassword, null); } throw notFound; } catch (Exception repositoryProblem) { throw new InternalAuthenticationServiceException( repositoryProblem.getMessage(), repositoryProblem); } if (loadedUser == null) { throw new InternalAuthenticationServiceException( "UserDetailsService returned null, which is an interface contract violation"); } return loadedUser; }再来看验证：
protected void additionalAuthenticationChecks(UserDetails userDetails, UsernamePasswordAuthenticationToken authentication) throws AuthenticationException { Object salt = null; if (this.saltSource != null) { salt = this.saltSource.getSalt(userDetails); } if (authentication.getCredentials() == null) { logger.debug("Authentication failed: no credentials provided"); throw new BadCredentialsException(messages.getMessage( "AbstractUserDetailsAuthenticationProvider.badCredentials", "Bad credentials")); } // 获取用户密码 String presentedPassword = authentication.getCredentials().toString(); // 比较passwordEncoder后的密码是否和userdetails的密码一致 if (!passwordEncoder.isPasswordValid(userDetails.getPassword(), presentedPassword, salt)) { logger.debug("Authentication failed: password does not match stored value"); throw new BadCredentialsException(messages.getMessage( "AbstractUserDetailsAuthenticationProvider.badCredentials", "Bad credentials")); } }小结：要自定义认证，使用DaoAuthenticationProvider，只需要为其提供PasswordEncoder和UserDetailsService就可以了。
定制 Authentication Managers
Spring Security提供了一个Builder类AuthenticationManagerBuilder，借助它可以快速实现自定义认证。
看官方源码说明：
SecurityBuilder used to create an AuthenticationManager . Allows for easily building in memory authentication, LDAP authentication, JDBC based authentication, adding UserDetailsService , and adding AuthenticationProvider's.
AuthenticationManagerBuilder可以用来Build一个AuthenticationManager，可以创建基于内存的认证、LDAP认证、 JDBC认证，以及添加UserDetailsService和AuthenticationProvider。
简单使用：
@Configuration@EnableWebSecurity@EnableGlobalMethodSecurity(prePostEnabled = true, securedEnabled = true)public class ApplicationSecurity extends WebSecurityConfigurerAdapter { public SecurityConfiguration(AuthenticationManagerBuilder authenticationManagerBuilder, UserDetailsService userDetailsService,TokenProvider tokenProvider,CorsFilter corsFilter, SecurityProblemSupport problemSupport) { this.authenticationManagerBuilder = authenticationManagerBuilder; this.userDetailsService = userDetailsService; this.tokenProvider = tokenProvider; this.corsFilter = corsFilter; this.problemSupport = problemSupport; } @PostConstruct public void init() { try { authenticationManagerBuilder .userDetailsService(userDetailsService) .passwordEncoder(passwordEncoder()); } catch (Exception e) { throw new BeanInitializationException("Security configuration failed", e); } } @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() .antMatchers("/api/register").permitAll() .antMatchers("/api/activate").permitAll() .antMatchers("/api/authenticate").permitAll() .antMatchers("/api/account/reset-password/init").permitAll() .antMatchers("/api/account/reset-password/finish").permitAll() .antMatchers("/api/profile-info").permitAll() .antMatchers("/api/**").authenticated() .antMatchers("/management/health").permitAll() .antMatchers("/management/**").hasAuthority(AuthoritiesConstants.ADMIN) .antMatchers("/v2/api-docs/**").permitAll() .antMatchers("/swagger-resources/configuration/ui").permitAll() .antMatchers("/swagger-ui/index.html").hasAuthority(AuthoritiesConstants.ADMIN) .and() .apply(securityConfigurerAdapter()); }}授权与访问控制
一旦认证成功，我们可以继续进行授权，授权是通过AccessDecisionManager来实现的。框架有三种实现，默认是AffirmativeBased，通过AccessDecisionVoter决策，有点像ProviderManager委托给AuthenticationProviders来认证。
public void decide(Authentication authentication, Object object, Collection<ConfigAttribute> configAttributes) throws AccessDeniedException { int deny = 0; // 遍历DecisionVoter for (AccessDecisionVoter voter : getDecisionVoters()) { // 投票 int result = voter.vote(authentication, object, configAttributes); if (logger.isDebugEnabled()) { logger.debug("Voter: " + voter + ", returned: " + result); } switch (result) { case AccessDecisionVoter.ACCESS_GRANTED: return; case AccessDecisionVoter.ACCESS_DENIED: deny++; break; default: break; } } // 一票否决 if (deny > 0) { throw new AccessDeniedException(messages.getMessage( "AbstractAccessDecisionManager.accessDenied", "Access is denied")); } // To get this far, every AccessDecisionVoter abstained checkAllowIfAllAbstainDecisions(); }来看AccessDecisionVoter：
boolean supports(ConfigAttribute attribute);boolean supports(Class<?> clazz);int vote(Authentication authentication, S object, Collection<ConfigAttribute> attributes);
object是用户要访问的资源，ConfigAttribute则是访问object要满足的条件，通常payload是字符串，比如ROLE_ADMIN 。所以我们来看下RoleVoter的实现，其核心就是从authentication提取出GrantedAuthority，然后和ConfigAttribute比较是否满足条件。
public boolean supports(ConfigAttribute attribute) { if ((attribute.getAttribute() != null) && attribute.getAttribute().startsWith(getRolePrefix())) { return true; } else { return false; } } public boolean supports(Class<?> clazz) { return true; }public int vote(Authentication authentication, Object object, Collection<ConfigAttribute> attributes) { if(authentication == null) { return ACCESS_DENIED; } int result = ACCESS_ABSTAIN; // 获取GrantedAuthority信息 Collection<? extends GrantedAuthority> authorities = extractAuthorities(authentication); for (ConfigAttribute attribute : attributes) { if (this.supports(attribute)) { // 默认拒绝访问 result = ACCESS_DENIED; // Attempt to find a matching granted authority for (GrantedAuthority authority : authorities) { // 判断是否有匹配的 authority if (attribute.getAttribute().equals(authority.getAuthority())) { // 可访问 return ACCESS_GRANTED; } } } } return result; }这里要疑问，ConfigAttribute哪来的？其实就是上面ApplicationSecurity的configure里的。
web security 如何实现
Web层中的Spring Security（用于UI和HTTP后端）基于Servlet Filters，下图显示了单个HTTP请求的处理程序的典型分层。
Spring Security通过FilterChainProxy作为单一的Filter注册到web层，Proxy内部的Filter。
FilterChainProxy相当于一个filter的容器，通过VirtualFilterChain来依次调用各个内部filter
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { boolean clearContext = request.getAttribute(FILTER_APPLIED) == null; if (clearContext) { try { request.setAttribute(FILTER_APPLIED, Boolean.TRUE); doFilterInternal(request, response, chain); } finally { SecurityContextHolder.clearContext(); request.removeAttribute(FILTER_APPLIED); } } else { doFilterInternal(request, response, chain); } } private void doFilterInternal(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { FirewalledRequest fwRequest = firewall .getFirewalledRequest((HttpServletRequest) request); HttpServletResponse fwResponse = firewall .getFirewalledResponse((HttpServletResponse) response); List<Filter> filters = getFilters(fwRequest); if (filters == null || filters.size() == 0) { if (logger.isDebugEnabled()) { logger.debug(UrlUtils.buildRequestUrl(fwRequest) + (filters == null ? " has no matching filters" : " has an empty filter list")); } fwRequest.reset(); chain.doFilter(fwRequest, fwResponse); return; } VirtualFilterChain vfc = new VirtualFilterChain(fwRequest, chain, filters); vfc.doFilter(fwRequest, fwResponse); } private static class VirtualFilterChain implements FilterChain { private final FilterChain originalChain; private final List<Filter> additionalFilters; private final FirewalledRequest firewalledRequest; private final int size; private int currentPosition = 0; private VirtualFilterChain(FirewalledRequest firewalledRequest, FilterChain chain, List<Filter> additionalFilters) { this.originalChain = chain; this.additionalFilters = additionalFilters; this.size = additionalFilters.size(); this.firewalledRequest = firewalledRequest; } public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException { if (currentPosition == size) { if (logger.isDebugEnabled()) { logger.debug(UrlUtils.buildRequestUrl(firewalledRequest) + " reached end of additional filter chain; proceeding with original chain"); } // Deactivate path stripping as we exit the security filter chain this.firewalledRequest.reset(); originalChain.doFilter(request, response); } else { currentPosition++; Filter nextFilter = additionalFilters.get(currentPosition - 1); if (logger.isDebugEnabled()) { logger.debug(UrlUtils.buildRequestUrl(firewalledRequest) + " at position " + currentPosition + " of " + size + " in additional filter chain; firing Filter: '" + nextFilter.getClass().getSimpleName() + "'"); } nextFilter.doFilter(request, response, this); } } }参考
https://spring.io/guides/topicals/spring-security-architecture/
https://docs.spring.io/spring-security/site/docs/5.0.5.RELEASE/reference/htmlsingle/#overall-architecture
总结
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