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

• 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

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：

1. 如果验证通过，返回Authentication（通常带上authenticated=true）。
2. 认证失败抛出AuthenticationException
3. 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

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

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作者：Jadepeng

出处：jqpeng的技术记事本--http://www.cnblogs.com/xiaoqi

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