基本概念

基本上，在所有的开发的系统中，都必须做认证(authentication)和授权(authorization)，以保证系统的安全性。

  • 认证是确认声明者的本身身份，其作为授权的上游衔接而存在
  • 鉴权是对声明者所声明的真实性进行确认的过程，其作为授权的下游衔接而存在

Spring Security 是一个功能强大且高度可定制的身份验证和访问控制框架。它是用于保护基于 Spring 的应用程序。

认证链路

1 用户名和密码被过滤器获取到，封装成Authentication,通常情况下是UsernamePasswordAuthenticationToken这个实现类。

2 AuthenticationManager 身份管理器负责验证这个Authentication

3 认证成功后，AuthenticationManager身份管理器返回一个被填充满了信息的（包括上面提到的权限信息，身份信息，细节信息，但密码通常会被移除）Authentication实例。

4 SecurityContextHolder安全上下文容器将第3步填充了信息的Authentication，通过SecurityContextHolder.getContext().setAuthentication(…)方法，设置到其中。

image-20240208155803862

http://kirito.iocoder.cn/2011121410543010.jpg

AuthenticationManager

AuthenticationManager（接口）是认证相关的核心接口，也是发起认证的出发点。AuthenticationManager一般不直接认证，AuthenticationManager接口的常用实现类ProviderManager 内部会维护一个List<AuthenticationProvider>列表，存放多种认证方式，实际上这是委托者模式的应用（Delegate）。

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public class ProviderManager implements AuthenticationManager, MessageSourceAware,
		InitializingBean {

    // 维护一个AuthenticationProvider列表
    private List<AuthenticationProvider> providers = Collections.emptyList();

    public Authentication authenticate(Authentication authentication)
          throws AuthenticationException {
       Class<? extends Authentication> toTest = authentication.getClass();
       AuthenticationException lastException = null;
       Authentication result = null;

       // 依次认证
       for (AuthenticationProvider provider : getProviders()) {
          if (!provider.supports(toTest)) {
             continue;
          }
          try {
             result = provider.authenticate(authentication);

             if (result != null) {
                copyDetails(authentication, result);
                break;
             }
          }
          ...
          catch (AuthenticationException e) {
             lastException = e;
          }
       }
       // 如果有Authentication信息，则直接返回
       if (result != null) {
			if (eraseCredentialsAfterAuthentication
					&& (result instanceof CredentialsContainer)) {
              	 //移除密码
				((CredentialsContainer) result).eraseCredentials();
			}
             //发布登录成功事件
			eventPublisher.publishAuthenticationSuccess(result);
			return result;
	   }
	   ...
       //执行到此，说明没有认证成功，包装异常信息
       if (lastException == null) {
          lastException = new ProviderNotFoundException(messages.getMessage(
                "ProviderManager.providerNotFound",
                new Object[] { toTest.getName() },
                "No AuthenticationProvider found for {0}"));
       }
       prepareException(lastException, authentication);
       throw lastException;
    }
}

ProviderManager 中的List，会依照次序去认证，认证成功则立即返回，若认证失败则返回null，下一个AuthenticationProvider会继续尝试认证，如果所有认证器都无法认证成功，则ProviderManager 会抛出一个ProviderNotFoundException异常。

DaoAuthenticationProvider：它获取用户提交的用户名和密码，比对其正确性，如果正确，返回一个数据库中的用户信息（假设用户信息被保存在数据库中）。

核心配置解读

WebSecurityConfigurerAdapter

拿 ruoyi 的 SecurityConfig 举例，它继承了 WebSecurityConfigurerAdapter。

适配器模式在spring中被广泛的使用，在配置中使用Adapter的好处便是，我们可以选择性的配置想要修改的那一部分配置，而不用覆盖其他不相关的配置。WebSecurityConfigurerAdapter中我们可以选择自己想要修改的内容，来进行重写，而其提供了三个configure重载方法。

  • configure(HttpSecurity)
  • configure(WebSecurity)
  • configure(AuthenticationManagerBuilder)
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/**
 * spring security配置
 *
 * @author ruoyi
 */
@EnableGlobalMethodSecurity(prePostEnabled = true, securedEnabled = true)
public class SecurityConfig extends WebSecurityConfigurerAdapter
{
    /**
     * 自定义用户认证逻辑
     */
    @Autowired
    private UserDetailsService userDetailsService;

    /**
     * 认证失败处理类
     */
    @Autowired
    private AuthenticationEntryPointImpl unauthorizedHandler;

    /**
     * 退出处理类
     */
    @Autowired
    private LogoutSuccessHandlerImpl logoutSuccessHandler;

    /**
     * token认证过滤器
     */
    @Autowired
    private JwtAuthenticationTokenFilter authenticationTokenFilter;

    /**
     * 跨域过滤器
     */
    @Autowired
    private CorsFilter corsFilter;

    /**
     * 允许匿名访问的地址
     */
    @Autowired
    private PermitAllUrlProperties permitAllUrl;

    /**
     * 解决 无法直接注入 AuthenticationManager
     *
     * @return
     * @throws Exception
     */
    @Bean
    @Override
    public AuthenticationManager authenticationManagerBean() throws Exception
    {
        return super.authenticationManagerBean();
    }

    /**
     * anyRequest          |   匹配所有请求路径
     * access              |   SpringEl表达式结果为true时可以访问
     * anonymous           |   匿名可以访问
     * denyAll             |   用户不能访问
     * fullyAuthenticated  |   用户完全认证可以访问（非remember-me下自动登录）
     * hasAnyAuthority     |   如果有参数，参数表示权限，则其中任何一个权限可以访问
     * hasAnyRole          |   如果有参数，参数表示角色，则其中任何一个角色可以访问
     * hasAuthority        |   如果有参数，参数表示权限，则其权限可以访问
     * hasIpAddress        |   如果有参数，参数表示IP地址，如果用户IP和参数匹配，则可以访问
     * hasRole             |   如果有参数，参数表示角色，则其角色可以访问
     * permitAll           |   用户可以任意访问
     * rememberMe          |   允许通过remember-me登录的用户访问
     * authenticated       |   用户登录后可访问
     */
    @Override
    protected void configure(HttpSecurity httpSecurity) throws Exception
    {
        // 注解标记允许匿名访问的url
        ExpressionUrlAuthorizationConfigurer<HttpSecurity>.ExpressionInterceptUrlRegistry registry = httpSecurity.authorizeRequests();
        permitAllUrl.getUrls().forEach(url -> registry.antMatchers(url).permitAll());

        httpSecurity
                // CSRF禁用，因为不使用session
                .csrf().disable()
                // 禁用HTTP响应标头
                .headers().cacheControl().disable().and()
                // 认证失败处理类
                .exceptionHandling().authenticationEntryPoint(unauthorizedHandler).and()
                // 基于token，所以不需要session
                .sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS).and()
                // 过滤请求
                .authorizeRequests()
                // 对于登录login 注册register 验证码captchaImage 允许匿名访问
                .antMatchers("/login", "/register", "/captchaImage").permitAll()
                // 静态资源，可匿名访问
                .antMatchers(HttpMethod.GET, "/", "/*.html", "/**/*.html", "/**/*.css", "/**/*.js", "/profile/**").permitAll()
                .antMatchers("/swagger-ui.html", "/swagger-resources/**", "/webjars/**", "/*/api-docs", "/druid/**").permitAll()
				.antMatchers("/test/*","/policy/*","/type/*").permitAll()
                // 除上面外的所有请求全部需要鉴权认证
                .anyRequest().authenticated()
                .and()
                .headers().frameOptions().disable();
        // 添加Logout filter
        httpSecurity.logout().logoutUrl("/logout").logoutSuccessHandler(logoutSuccessHandler);
        // 添加JWT filter
        httpSecurity.addFilterBefore(authenticationTokenFilter, UsernamePasswordAuthenticationFilter.class);
        // 添加CORS filter
        httpSecurity.addFilterBefore(corsFilter, JwtAuthenticationTokenFilter.class);
        httpSecurity.addFilterBefore(corsFilter, LogoutFilter.class);
    }

    /**
     * 强散列哈希加密实现
     */
    @Bean
    public BCryptPasswordEncoder bCryptPasswordEncoder()
    {
        return new BCryptPasswordEncoder();
    }

    /**
     * 身份认证接口
     */
    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception
    {
        auth.userDetailsService(userDetailsService).passwordEncoder(bCryptPasswordEncoder());
    }
}

HttpSecurity常用配置

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@Configuration
@EnableWebSecurity
public class CustomWebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/resources/**", "/signup", "/about").permitAll()
                .antMatchers("/admin/**").hasRole("ADMIN")
                .antMatchers("/db/**").access("hasRole('ADMIN') and hasRole('DBA')")
                .anyRequest().authenticated()
                .and()
            .formLogin()
                .usernameParameter("username")
                .passwordParameter("password")
                .failureForwardUrl("/login?error")
                .loginPage("/login")
                .permitAll()
                .and()
            .logout()
                .logoutUrl("/logout")
                .logoutSuccessUrl("/index")
                .permitAll()
                .and()
            .httpBasic()
                .disable();
    }
}

上述是一个使用Java Configuration配置HttpSecurity的典型配置，其中http作为根开始配置，每一个and()对应了一个模块的配置（等同于xml配置中的结束标签），并且and()返回了HttpSecurity本身，于是可以连续进行配置。他们配置的含义也非常容易通过变量本身来推测，

  • authorizeRequests()配置路径拦截，表明路径访问所对应的权限，角色，认证信息。
  • formLogin()对应表单认证相关的配置
  • logout()对应了注销相关的配置
  • httpBasic()可以配置basic登录
  • etc

WebSecurity常用配置

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@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    public void configure(WebSecurity web) throws Exception {
        web
            .ignoring()
            .antMatchers("/resources/**");
    }
}

AuthenticationManagerBuilder

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@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth
            .inMemoryAuthentication()
            .withUser("admin").password("admin").roles("USER");
    }
}

想要在WebSecurityConfigurerAdapter中进行认证相关的配置，可以使用configure(AuthenticationManagerBuilder auth)暴露一个AuthenticationManager的建造器：AuthenticationManagerBuilder 。如上所示，我们便完成了内存中用户的配置。

除了以上的示例代码，还有另外一种配置方法。

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@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
        auth
            .inMemoryAuthentication()
                .withUser("admin").password("admin").roles("USER");
    }
}

如果你的应用只有唯一一个WebSecurityConfigurerAdapter，那么他们之间的差距可以被忽略，从方法名可以看出两者的区别：

  • 使用@Autowired注入的AuthenticationManagerBuilder是全局的身份认证器，作用域可以跨越多个WebSecurityConfigurerAdapter，以及影响到基于Method的安全控制；
  • 而 protected configure()的方式则类似于一个匿名内部类，它的作用域局限于一个WebSecurityConfigurerAdapter内部。

授权链路

image-20240208154120807

UsernamePasswordAuthenticationFilter

整个调用流程是，先调用其父类 AbstractAuthenticationProcessingFilter.doFilter() 方法，然后再执行 UsernamePasswordAuthenticationFilter.attemptAuthentication() 方法进行验证；

AbstractAuthenticationProcessingFilter:

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public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {

		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;
		#1.判断当前的filter是否可以处理当前请求，不可以的话则交给下一个filter处理
		if (!requiresAuthentication(request, response)) {
			chain.doFilter(request, response);

			return;
		}

		if (logger.isDebugEnabled()) {
			logger.debug("Request is to process authentication");
		}

		Authentication authResult;

		try {
			#2.抽象方法由子类UsernamePasswordAuthenticationFilter实现
			authResult = attemptAuthentication(request, response);
			if (authResult == null) {
				// return immediately as subclass has indicated that it hasn't completed
				// authentication
				return;
			}
			#2.认证成功后，处理一些与session相关的方法 
			sessionStrategy.onAuthentication(authResult, request, response);
		}
		catch (InternalAuthenticationServiceException failed) {
			logger.error(
					"An internal error occurred while trying to authenticate the user.",
					failed);
			#3.认证失败后的的一些操作
			unsuccessfulAuthentication(request, response, failed);

			return;
		}
		catch (AuthenticationException failed) {
			// Authentication failed
			unsuccessfulAuthentication(request, response, failed);

			return;
		}

		// Authentication success
		if (continueChainBeforeSuccessfulAuthentication) {
			chain.doFilter(request, response);
		}
		#3. 认证成功后的相关回调方法 主要将当前的认证放到SecurityContextHolder中
		successfulAuthentication(request, response, chain, authResult);
	}

整个程序的执行流程如下:

  1. 判断filter是否可以处理当前的请求，如果不可以则放行交给下一个filter
  2. 调用抽象方法attemptAuthentication进行验证，该方法由子类UsernamePasswordAuthenticationFilter实现
  3. 认证成功以后，回调一些与 session 相关的方法；
  4. 认证成功以后，认证成功后的相关回调方法；认证成功以后，认证成功后的相关回调方法；
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protected void successfulAuthentication(HttpServletRequest request,
			HttpServletResponse response, FilterChain chain, Authentication authResult)
			throws IOException, ServletException {

		if (logger.isDebugEnabled()) {
			logger.debug("Authentication success. Updating SecurityContextHolder to contain: "
					+ authResult);
		}

		SecurityContextHolder.getContext().setAuthentication(authResult);

		rememberMeServices.loginSuccess(request, response, authResult);

		// Fire event
		if (this.eventPublisher != null) {
			eventPublisher.publishEvent(new InteractiveAuthenticationSuccessEvent(
					authResult, this.getClass()));
		}

		successHandler.onAuthenticationSuccess(request, response, authResult);
	}
  1. 将当前认证成功的 Authentication 放置到 SecurityContextHolder 中；
  2. 调用其它可扩展的 handlers 继续处理该认证成功以后的回调事件；（实现AuthenticationSuccessHandler接口即可）

UsernamePasswordAuthenticationFilter: 

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public Authentication attemptAuthentication(HttpServletRequest request,
			HttpServletResponse response) throws AuthenticationException {
		#1.判断请求的方法必须为POST请求
		if (postOnly && !request.getMethod().equals("POST")) {
			throw new AuthenticationServiceException(
					"Authentication method not supported: " + request.getMethod());
		}
		#2.从request中获取username和password
		String username = obtainUsername(request);
		String password = obtainPassword(request);

		if (username == null) {
			username = "";
		}

		if (password == null) {
			password = "";
		}

		username = username.trim();
		#3.构建UsernamePasswordAuthenticationToken（两个参数的构造方法setAuthenticated(false)）
		UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(
				username, password);

		// Allow subclasses to set the "details" property
		setDetails(request, authRequest);
		#4. 调用 AuthenticationManager 进行验证（子类ProviderManager遍历所有的AuthenticationProvider认证）
		return this.getAuthenticationManager().authenticate(authRequest);
	}
  1. 认证请求的方法必须为POST
  2. 从request中获取 username 和 password
  3. 封装Authenticaiton的实现类UsernamePasswordAuthenticationToken，（UsernamePasswordAuthenticationToken调用两个参数的构造方法setAuthenticated(false)）
  4. 调用 AuthenticationManager 的 authenticate 方法进行验证；可参考ProviderManager部分

AnonymousAuthenticationFilter

从上图中过滤器的执行顺序图中可以看出AnonymousAuthenticationFilter过滤器是在UsernamePasswordAuthenticationFilter等过滤器之后，如果它前面的过滤器都没有认证成功，Spring Security则为当前的SecurityContextHolder中添加一个Authenticaiton 的匿名实现类AnonymousAuthenticationToken;

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public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
		#1.如果前面的过滤器都没认证通过，则SecurityContextHolder中Authentication为空
		if (SecurityContextHolder.getContext().getAuthentication() == null) {
			#2.为当前的SecurityContextHolder中添加一个匿名的AnonymousAuthenticationToken
			SecurityContextHolder.getContext().setAuthentication(
					createAuthentication((HttpServletRequest) req));

			if (logger.isDebugEnabled()) {
				logger.debug("Populated SecurityContextHolder with anonymous token: '"
						+ SecurityContextHolder.getContext().getAuthentication() + "'");
			}
		}
		else {
			if (logger.isDebugEnabled()) {
				logger.debug("SecurityContextHolder not populated with anonymous token, as it already contained: '"
						+ SecurityContextHolder.getContext().getAuthentication() + "'");
			}
		}

		chain.doFilter(req, res);
	}

	#3.创建匿名的AnonymousAuthenticationToken
	protected Authentication createAuthentication(HttpServletRequest request) {
		AnonymousAuthenticationToken auth = new AnonymousAuthenticationToken(key,
				principal, authorities);
		auth.setDetails(authenticationDetailsSource.buildDetails(request));

		return auth;
	}
	
		/**
	 * Creates a filter with a principal named "anonymousUser" and the single authority
	 * "ROLE_ANONYMOUS".
	 *
	 * @param key the key to identify tokens created by this filter
	 */
	 #.创建一个用户名为anonymousUser 授权为ROLE_ANONYMOUS
	public AnonymousAuthenticationFilter(String key) {
		this(key, "anonymousUser", AuthorityUtils.createAuthorityList("ROLE_ANONYMOUS"));
	}
  1. 判断SecurityContextHolder中Authentication为否为空；
  2. 如果空则为当前的SecurityContextHolder中添加一个匿名的AnonymousAuthenticationToken（用户名为 anonymousUser 的AnonymousAuthenticationToken）

ExceptionTranslationFilter

异常处理过滤器,该过滤器用来处理在系统认证授权过程中抛出的异常（也就是下一个过滤器FilterSecurityInterceptor）,主要是 处理 AuthenticationException 和 AccessDeniedException 。

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public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;

		try {
			chain.doFilter(request, response);

			logger.debug("Chain processed normally");
		}
		catch (IOException ex) {
			throw ex;
		}
		catch (Exception ex) {
			// Try to extract a SpringSecurityException from the stacktrace
			#.判断是不是AuthenticationException
			Throwable[] causeChain = throwableAnalyzer.determineCauseChain(ex);
			RuntimeException ase = (AuthenticationException) throwableAnalyzer
					.getFirstThrowableOfType(AuthenticationException.class, causeChain);

			if (ase == null) {
				#. 判断是不是AccessDeniedException
				ase = (AccessDeniedException) throwableAnalyzer.getFirstThrowableOfType(
						AccessDeniedException.class, causeChain);
			}

			if (ase != null) {
				handleSpringSecurityException(request, response, chain, ase);
			}
			else {
				// Rethrow ServletExceptions and RuntimeExceptions as-is
				if (ex instanceof ServletException) {
					throw (ServletException) ex;
				}
				else if (ex instanceof RuntimeException) {
					throw (RuntimeException) ex;
				}

				// Wrap other Exceptions. This shouldn't actually happen
				// as we've already covered all the possibilities for doFilter
				throw new RuntimeException(ex);
			}
		}
	}

FilterSecurityInterceptor

此过滤器为认证授权过滤器链中最后一个过滤器，该过滤器之后就是请求真正的/persons 服务

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public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		FilterInvocation fi = new FilterInvocation(request, response, chain);
		invoke(fi);
	}

public void invoke(FilterInvocation fi) throws IOException, ServletException {
		if ((fi.getRequest() != null)
				&& (fi.getRequest().getAttribute(FILTER_APPLIED) != null)
				&& observeOncePerRequest) {
			// filter already applied to this request and user wants us to observe
			// once-per-request handling, so don't re-do security checking
			fi.getChain().doFilter(fi.getRequest(), fi.getResponse());
		}
		else {
			// first time this request being called, so perform security checking
			if (fi.getRequest() != null) {
				fi.getRequest().setAttribute(FILTER_APPLIED, Boolean.TRUE);
			}
			#1. before invocation重要
			InterceptorStatusToken token = super.beforeInvocation(fi);

			try {
				#2. 可以理解开始请求真正的 /persons 服务
				fi.getChain().doFilter(fi.getRequest(), fi.getResponse());
			}
			finally {
				super.finallyInvocation(token);
			}
			#3. after Invocation
			super.afterInvocation(token, null);
		}
	}
  1. before invocation重要
  2. 请求真正的 /persons 服务
  3. after Invocation

三个部分中，最重要的是 #1，该过程中会调用 AccessDecisionManager 来验证当前已认证成功的用户是否有权限访问该资源；

before invocation: AccessDecisionManager

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protected InterceptorStatusToken beforeInvocation(Object object) {
		...

		Collection<ConfigAttribute> attributes = this.obtainSecurityMetadataSource()
				.getAttributes(object);

		...
		Authentication authenticated = authenticateIfRequired();

		// Attempt authorization
		try {
			#1.重点
			this.accessDecisionManager.decide(authenticated, object, attributes);
		}
		catch (AccessDeniedException accessDeniedException) {
			publishEvent(new AuthorizationFailureEvent(object, attributes, authenticated,accessDeniedException));

			throw accessDeniedException;
		}

		...
	}

authenticated就是当前认证的Authentication，object为当前请求的 url:/persons, getAttributes方法就是使用当前的访问资源路径去匹配我们自己定义的匹配规则。

AccessDecisionManager 是如何授权的？

Spring Security默认使用AffirmativeBased实现AccessDecisionManager 的 decide 方法来实现授权

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public void decide(Authentication authentication, Object object,
			Collection<ConfigAttribute> configAttributes) throws AccessDeniedException {
		int deny = 0;
		#1.调用AccessDecisionVoter 进行vote(投票)
		for (AccessDecisionVoter voter : getDecisionVoters()) {
			int result = voter.vote(authentication, object, configAttributes);

			if (logger.isDebugEnabled()) {
				logger.debug("Voter: " + voter + ", returned: " + result);
			}

			switch (result) {
			#1.1只要有voter投票为ACCESS_GRANTED，则通过 直接返回
			case AccessDecisionVoter.ACCESS_GRANTED://1
				return;
			@#1.2只要有voter投票为ACCESS_DENIED，则记录一下
			case AccessDecisionVoter.ACCESS_DENIED://-1
				deny++;

				break;

			default:
				break;
			}
		}

		if (deny > 0) {
		#2.如果有一个及以上AccessDecisionVoter(姑且称之为投票者吧)都投ACCESS_DENIED，则直接就不通过了
			throw new AccessDeniedException(messages.getMessage(
					"AbstractAccessDecisionManager.accessDenied", "Access is denied"));
		}

		// To get this far, every AccessDecisionVoter abstained
		checkAllowIfAllAbstainDecisions();
	}
  1. 调用AccessDecisionVoter 进行vote(投票)
  2. 只要有投通过（ACCESS_GRANTED）票，则直接判为通过。
  3. 如果没有投通过则 deny++ ,最后判断if（deny>0 抛出AccessDeniedException（未授权）

SpringSecurityFilterChain过滤器加载流程

DelegatingFilterProxy

它的包结构：org.springframework.web.filter，它本身是 Spring Web 包中的类，并不是 SpringSecurity 中的类。因为 Spring 考虑到了多种使用场景，自然希望将侵入性降到最低，所以使用了这个委托代理类来代理真正的 SpringSecurityFilterChain。

DelegatingFilterProxy 实现了 javax.servlet.Filter 接口，使得它可以作为一个 java web 的标准过滤器，其职责也很简单，只负责调用真正的 SpringSecurityFilterChain。

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public class DelegatingFilterProxy extends GenericFilterBean {

   private WebApplicationContext webApplicationContext;
   // springSecurityFilterChain
   private String targetBeanName;
   // <1> 关键点
   private volatile Filter delegate;
   private final Object delegateMonitor = new Object();

   public DelegatingFilterProxy(String targetBeanName, WebApplicationContext wac) {
      Assert.hasText(targetBeanName, "Target Filter bean name must not be null or empty");
      this.setTargetBeanName(targetBeanName);
      this.webApplicationContext = wac;
      if (wac != null) {
         this.setEnvironment(wac.getEnvironment());
      }
   }

   @Override
   protected void initFilterBean() throws ServletException {
      synchronized (this.delegateMonitor) {
         if (this.delegate == null) {
            if (this.targetBeanName == null) {
               this.targetBeanName = getFilterName();
            }
            // Fetch Spring root application context and initialize the delegate early,
            // if possible. If the root application context will be started after this
            // filter proxy, we'll have to resort to lazy initialization.
            WebApplicationContext wac = findWebApplicationContext();
            if (wac != null) {
               this.delegate = initDelegate(wac);
            }
         }
      }
   }

   @Override
   public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
         throws ServletException, IOException {

      // 过滤器代理支持懒加载
      Filter delegateToUse = this.delegate;
      if (delegateToUse == null) {
         synchronized (this.delegateMonitor) {
            delegateToUse = this.delegate;
            if (delegateToUse == null) {
               WebApplicationContext wac = findWebApplicationContext();
               delegateToUse = initDelegate(wac);
            }
            this.delegate = delegateToUse;
         }
      }

      // 让代理过滤器执行实际的过滤行为
      invokeDelegate(delegateToUse, request, response, filterChain);
   }

   // 初始化过滤器代理
   // <2>
   protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
      Filter delegate = wac.getBean(getTargetBeanName(), Filter.class);
      if (isTargetFilterLifecycle()) {
         delegate.init(getFilterConfig());
      }
      return delegate;
   }


   // 调用代理过滤器
   protected void invokeDelegate(
         Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain)
         throws ServletException, IOException {
      delegate.doFilter(request, response, filterChain);
   }

}

<1> 可以发现整个 DelegatingFilterProxy 的逻辑就是为了调用 private volatile Filter delegate;

<2> 可以看到，DelegatingFilterProxy 尝试去容器中获取名为 targetBeanName 的类，而 targetBeanName 的默认值便是 Filter 的名称，也就是 springSecurityFilterChain

DelegatingFilterProxy 只是名称和 targetBeanName 叫 springSecurityFilterChain，真正容器中的 Bean(name=”springSecurityFilterChain”) 其实另有其人——通过 debug，我们发现了真正的 springSecurityFilterChain — FilterChainProxy。

SpringSecurityFilterChain 是什么时候被放进去的？

这就得说到老朋友 WebSecurity 了，还记得一般我们都会选择使用 @EnableWebSecurity 和 WebSecurityConfigurerAdapter 来进行 web 安全配置吗，来到 WebSecurity 的源码：

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public final class WebSecurity extends
      AbstractConfiguredSecurityBuilder<Filter, WebSecurity> implements
      SecurityBuilder<Filter>, ApplicationContextAware {

    @Override
	protected Filter performBuild() throws Exception {
		int chainSize = ignoredRequests.size() + securityFilterChainBuilders.size();
		List<SecurityFilterChain> securityFilterChains = new ArrayList<SecurityFilterChain>(
				chainSize);
		for (RequestMatcher ignoredRequest : ignoredRequests) {
			securityFilterChains.add(new DefaultSecurityFilterChain(ignoredRequest));
		}
		for (SecurityBuilder<? extends SecurityFilterChain> securityFilterChainBuilder : securityFilterChainBuilders) {
			securityFilterChains.add(securityFilterChainBuilder.build());
		}
        // <1> FilterChainProxy 由 WebSecurity 构建
		FilterChainProxy filterChainProxy = new FilterChainProxy(securityFilterChains);
		if (httpFirewall != null) {
			filterChainProxy.setFirewall(httpFirewall);
		}
		filterChainProxy.afterPropertiesSet();

		Filter result = filterChainProxy;
		postBuildAction.run();
		return result;
	}
}

<1> 最终定位到 WebSecurity 的 performBuild 方法，我们之前配置了一堆参数的 WebSecurity 最终帮助我们构建了 FilterChainProxy。

并且，最终在 org.springframework.security.config.annotation.web.configuration.WebSecurityConfiguration中被注册为默认名称为 SpringSecurityFilterChain。

FilterChainProxy

它才是真正的 springSecurityFilterChain，我们来看看它的源码（有删减，不影响理解）。

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public class FilterChainProxy extends GenericFilterBean {
   // <1> 包含了多个SecurityFilterChain
   private List<SecurityFilterChain> filterChains;

   public FilterChainProxy(SecurityFilterChain chain) {
      this(Arrays.asList(chain));
   }

   public FilterChainProxy(List<SecurityFilterChain> filterChains) {
      this.filterChains = filterChains;
   }

   @Override
   public void afterPropertiesSet() {
      filterChainValidator.validate(this);
   }

   public void doFilter(ServletRequest request, ServletResponse response,
         FilterChain chain) throws IOException, ServletException {
         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);
	  // <1>
      List<Filter> filters = getFilters(fwRequest);

      if (filters == null || filters.size() == 0) {
         fwRequest.reset();
         chain.doFilter(fwRequest, fwResponse);
         return;
      }

      VirtualFilterChain vfc = new VirtualFilterChain(fwRequest, chain, filters);
      vfc.doFilter(fwRequest, fwResponse);
   }

   /**
    * <1> 可能会有多个过滤器链，返回第一个和请求URL匹配的过滤器链
    */
   private List<Filter> getFilters(HttpServletRequest request) {
      for (SecurityFilterChain chain : filterChains) {
         if (chain.matches(request)) {
            return chain.getFilters();
         }
      }
      return null;
   }

}

看 FilterChainProxy 的名字就可以发现，它依旧不是真正实施过滤的类，它内部维护了一个 SecurityFilterChain，这个过滤器链才是请求真正对应的过滤器链，并且同一个 Spring 环境下，可能同时存在多个安全过滤器链，如 private List filterChains 所示，需要经过 chain.matches(request) 判断到底哪个过滤器链匹配成功，每个 request 最多只会经过一个 SecurityFilterChain。