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 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：
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 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;
}
在UserDetails里说了，GrantedAuthority可以理解为角色，例如 ROLE_ADMINISTRATOR or ROLE_HR_SUPERVISOR。
小结
SecurityContextHolder, 用来访问 SecurityContext.
SecurityContext, 用来存储Authentication .
Authentication, 代表凭证.
GrantedAuthority, 代表权限.
UserDetails, 用户信息.
UserDetailsService,获取用户信息.
Authentication认证
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：
如果验证通过，返回Authentication（通常带上authenticated=true）。
认证失败抛出AuthenticationException
如果无法确定，则返回null
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。
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：
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：
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);
}
}
}