Spring Security是一个能够为基于Spring的企业应用系统提供声明式的安全访问控制解决方案的安全框架。它提供了一组可以在Spring应用上下文中配置的Bean，充分利用了Spring IoC，DI（控制反转Inversion of Control ,DI:Dependency Injection 依赖注入）和AOP（面向切面编程）功能，为应用系统提供声明式的安全访问控制功能，减少了为企业系统安全控制编写大量重复代码的工作。

类图

为了方便理解Spring Security认证流程，特意画了如下的类图，包含相关的核心认证类

概述

核心验证器

AuthenticationManager

该对象提供了认证方法的入口，接收一个Authentiaton对象作为参数;

public interface AuthenticationManager {Authentication authenticate(Authentication authentication)throws AuthenticationException;
}

ProviderManager

它是 AuthenticationManager 的一个实现类，提供了基本的认证逻辑和方法；它包含了一个 List<AuthenticationProvider> 对象，通过 AuthenticationProvider 接口来扩展出不同的认证提供者(当Spring Security默认提供的实现类不能满足需求的时候可以扩展AuthenticationProvider 覆盖supports(Class<?> authentication)方法)；

验证逻辑

AuthenticationManager 接收 Authentication 对象作为参数，并通过 authenticate(Authentication) 方法对其进行验证；AuthenticationProvider实现类用来支撑对 Authentication 对象的验证动作；UsernamePasswordAuthenticationToken实现了 Authentication主要是将用户输入的用户名和密码进行封装，并供给 AuthenticationManager 进行验证；验证完成以后将返回一个认证成功的 Authentication 对象；

Authentication

Authentication对象中的主要方法

public interface Authentication extends Principal, Serializable {//#1.权限结合，可使用AuthorityUtils.commaSeparatedStringToAuthorityList("admin,ROLE_ADMIN")返回字符串权限集合Collection<? extends GrantedAuthority> getAuthorities();//#2.用户名密码认证时可以理解为密码Object getCredentials();//#3.认证时包含的一些信息。Object getDetails();//#4.用户名密码认证时可理解时用户名Object getPrincipal();#5.是否被认证，认证为true boolean isAuthenticated();#6.设置是否能被认证void setAuthenticated(boolean isAuthenticated) throws IllegalArgumentException;

ProviderManager

ProviderManager是AuthenticationManager的实现类，提供了基本认证实现逻辑和流程；

public Authentication authenticate(Authentication authentication)throws AuthenticationException {//#1.获取当前的Authentication的认证类型Class<? extends Authentication> toTest = authentication.getClass();AuthenticationException lastException = null;Authentication result = null;boolean debug = logger.isDebugEnabled();//#2.遍历所有的providers使用supports方法判断该provider是否支持当前的认证类型，不支持的话继续遍历for (AuthenticationProvider provider : getProviders()) {if (!provider.supports(toTest)) {continue;}if (debug) {logger.debug("Authentication attempt using "+ provider.getClass().getName());}try {#3.支持的话调用provider的authenticat方法认证result = provider.authenticate(authentication);if (result != null) {#4.认证通过的话重新生成Authentication对应的TokencopyDetails(authentication, result);break;}}catch (AccountStatusException e) {prepareException(e, authentication);// SEC-546: Avoid polling additional providers if auth failure is due to// invalid account statusthrow 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 {#5.如果#1 没有验证通过，则使用父类型AuthenticationManager进行验证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;}}#6. 是否擦出敏感信息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;}

1. 遍历所有的 Providers，然后依次执行该 Provider 的验证方法
   • 如果某一个 Provider 验证成功，则跳出循环不再执行后续的验证；
   • 如果验证成功，会将返回的 result 既 Authentication 对象进一步封装为 Authentication Token； 比如 UsernamePasswordAuthenticationToken、RememberMeAuthenticationToken 等；这些 Authentication Token 也都继承自 Authentication 对象；
2. 如果 #1 没有任何一个 Provider 验证成功，则试图使用其 parent Authentication Manager 进行验证；
3. 是否需要擦除密码等敏感信息；

AuthenticationProvider

ProviderManager 通过 AuthenticationProvider 扩展出更多的验证提供的方式；而 AuthenticationProvider 本身也就是一个接口，从类图中我们可以看出它的实现类AbstractUserDetailsAuthenticationProvider和AbstractUserDetailsAuthenticationProvider的子类DaoAuthenticationProvider。DaoAuthenticationProvider是Spring Security中一个核心的Provider,对所有的数据库提供了基本方法和入口。

DaoAuthenticationProvider

DaoAuthenticationProvider主要做了以下事情

1. 对用户身份尽心加密操作；

     #1.可直接返回BCryptPasswordEncoder，也可以自己实现该接口使用自己的加密算法核心方法String encode(CharSequence rawPassword);和boolean matches(CharSequence rawPassword, String encodedPassword);
   

private PasswordEncoder passwordEncoder;

2. 实现了 `AbstractUserDetailsAuthenticationProvider` 两个抽象方法，1. 获取用户信息的扩展点```java
protected final UserDetails retrieveUser(String username,UsernamePasswordAuthenticationToken authentication)throws AuthenticationException {UserDetails loadedUser;try {loadedUser = this.getUserDetailsService().loadUserByUsername(username);}

主要是通过注入`UserDetailsService`接口对象，并调用其接口方法 `loadUserByUsername(String username)` 获取得到相关的用户信息。`UserDetailsService`接口非常重要。
2. 实现 additionalAuthenticationChecks 的验证方法(主要验证密码)；

AbstractUserDetailsAuthenticationProvider

AbstractUserDetailsAuthenticationProvider为DaoAuthenticationProvider提供了基本的认证方法；

public Authentication authenticate(Authentication authentication)throws AuthenticationException {Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication,messages.getMessage("AbstractUserDetailsAuthenticationProvider.onlySupports","Only UsernamePasswordAuthenticationToken is supported"));// Determine usernameString username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED": authentication.getName();boolean cacheWasUsed = true;UserDetails user = this.userCache.getUserFromCache(username);if (user == null) {cacheWasUsed = false;try {#1.获取用户信息由子类实现即DaoAuthenticationProvideruser = 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 {#2.前检查由DefaultPreAuthenticationChecks类实现（主要判断当前用户是否锁定，过期，冻结User接口）preAuthenticationChecks.check(user);#3.子类实现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;}}#4.检测用户密码是否过期对应#2 的User接口postAuthenticationChecks.check(user);if (!cacheWasUsed) {this.userCache.putUserInCache(user);}Object principalToReturn = user;if (forcePrincipalAsString) {principalToReturn = user.getUsername();}return createSuccessAuthentication(principalToReturn, authentication, user);}

AbstractUserDetailsAuthenticationProvider主要实现了AuthenticationProvider的接口方法authenticate 并提供了相关的验证逻辑；

1. 获取用户返回UserDetails AbstractUserDetailsAuthenticationProvider定义了一个抽象的方法

protected abstract UserDetails retrieveUser(String username, UsernamePasswordAuthenticationToken authentication) throws AuthenticationException;

2. 三步验证工作1. preAuthenticationChecks2. additionalAuthenticationChecks（抽象方法，子类实现）3. postAuthenticationChecks
3. 将已通过验证的用户信息封装成 UsernamePasswordAuthenticationToken 对象并返回；该对象封装了用户的身份信息，以及相应的权限信息，相关源码如下，```java
protected Authentication createSuccessAuthentication(Object principal,UsernamePasswordAuthenticationToken result = new UsernamePasswordAuthenticationToken(principal, authentication.getCredentials(),authoritiesMapper.mapAuthorities(user.getAuthorities()));result.setDetails(authentication.getDetails());return result;}

UserDetailsService

UserDetailsService是一个接口，提供了一个方法

public interface UserDetailsService {UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;
}

通过用户名 username 调用方法 loadUserByUsername 返回了一个UserDetails接口对象（对应AbstractUserDetailsAuthenticationProvider的三步验证方法）；

public interface UserDetails extends Serializable {#1.权限集合Collection<? extends GrantedAuthority> getAuthorities();#2.密码    String getPassword();#3.用户民String getUsername();#4.用户是否过期boolean isAccountNonExpired();#5.是否锁定  boolean isAccountNonLocked();#6.用户密码是否过期    boolean isCredentialsNonExpired();#7.账号是否可用（可理解为是否删除）boolean isEnabled();
}

Spring 为UserDetailsService默认提供了一个实现类 org.springframework.security.core.userdetails.jdbc.JdbcDaoImpl

JdbcUserDetailsManager

该实现类主要是提供基于JDBC对 User 进行增、删、查、改的方法

public class JdbcUserDetailsManager extends JdbcDaoImpl implements UserDetailsManager,GroupManager {// ~ Static fields/initializers// =====================================================================================// UserDetailsManager SQL#1.定义了一些列对数据库操作的语句public static final String DEF_CREATE_USER_SQL = "insert into users (username, password, enabled) values (?,?,?)";public static final String DEF_DELETE_USER_SQL = "delete from users where username = ?";public static final String DEF_UPDATE_USER_SQL = "update users set password = ?, enabled = ? where username = ?";public static final String DEF_INSERT_AUTHORITY_SQL = "insert into authorities (username, authority) values (?,?)";public static final String DEF_DELETE_USER_AUTHORITIES_SQL = "delete from authorities where username = ?";public static final String DEF_USER_EXISTS_SQL = "select username from users where username = ?";public static final String DEF_CHANGE_PASSWORD_SQL = "update users set password = ? where username = ?";

InMemoryUserDetailsManager

该实现类主要是提供基于内存对 User 进行增、删、查、改的方法 `public class InMemoryUserDetailsManager implements UserDetailsManager { protected final Log logger = LogFactory.getLog(getClass()); #1.用MAP 存储 private final Map<String, MutableUserDetails> users = new HashMap<String, MutableUserDetails>();

private AuthenticationManager authenticationManager;public InMemoryUserDetailsManager() {
}public InMemoryUserDetailsManager(Collection<UserDetails> users) {for (UserDetails user : users) {createUser(user);}
}`

总结

UserDetailsService接口作为桥梁，是DaoAuthenticationProvier与特定用户信息来源进行解耦的地方，UserDetailsService由UserDetails和UserDetailsManager所构成；UserDetails和UserDetailsManager各司其责，一个是对基本用户信息进行封装，一个是对基本用户信息进行管理；

特别注意，UserDetailsService、UserDetails以及UserDetailsManager都是可被用户自定义的扩展点，我们可以继承这些接口提供自己的读取用户来源和管理用户的方法，比如我们可以自己实现一个 与特定 ORM 框架，比如 Mybatis 或者 Hibernate，相关的UserDetailsService和UserDetailsManager；

时序图