Spring Security(3)：配置与自动配置的介绍及源码分析

基于注解的配置（Java Configuration）从Spring Security 3.2开始就已经支持，本篇基于Spring boot注解的配置进行讲解，如果需要基于XML配置（Security Namespace Configuration），可查阅Spring Security官网：https://docs.spring.io/spring-security/site/docs/5.1.5.RELEASE/reference/htmlsingle/#ns-config

基于Maven的Spring及Spring Boot配置不再赘述，想要配置Spring Security，只需要@EnableWebSecurity注解。如果需要自定义一些配置，则需要和继承WebSecurityConfigurerAdapter后，覆盖某些方法：

@EnableWebSecurity
public class MySecurityConfig extends WebSecurityConfigurerAdapter { }

本节主要讲通过@EnableWebSecurity的默认配置。下节来讲通过继承WebSecurityConfigurerAdapter的自定义配置。

[2019/06/04 ADD]

在SpringBoot中，只要你加入spring-boot-starter-security包到项目中，即使不配置@EnableWebSecurity和WebSecurityConfigurerAdapter，SpringBoot也会自动给我们添加这两个配置。具体可以看SpringBootWebSecurityConfiguration及WebSecurityEnablerConfiguration。

/**
 * The default configuration for web security. It relies on Spring Security's
 * content-negotiation strategy to determine what sort of authentication to use. If the
 * user specifies their own {@link WebSecurityConfigurerAdapter}, this will back-off
 * completely and the users should specify all the bits that they want to configure as
 * part of the custom security configuration.
 *
 * @author Madhura Bhave
 * @since 2.0.0
 */
@Configuration
@ConditionalOnClass(WebSecurityConfigurerAdapter.class)
@ConditionalOnMissingBean(WebSecurityConfigurerAdapter.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
public class SpringBootWebSecurityConfiguration {
    @Configuration
    @Order(SecurityProperties.BASIC_AUTH_ORDER)
    static class DefaultConfigurerAdapter extends WebSecurityConfigurerAdapter {
    }
}

/**
 * If there is a bean of type WebSecurityConfigurerAdapter, this adds the
 * {@link EnableWebSecurity} annotation. This will make sure that the annotation is
 * present with default security auto-configuration and also if the user adds custom
 * security and forgets to add the annotation. If {@link EnableWebSecurity} has already
 * been added or if a bean with name {@value BeanIds#SPRING_SECURITY_FILTER_CHAIN} has
 * been configured by the user, this will back-off.
 *
 * @author Madhura Bhave
 * @since 2.0.0
 */
@Configuration
@ConditionalOnBean(WebSecurityConfigurerAdapter.class)
@ConditionalOnMissingBean(name = BeanIds.SPRING_SECURITY_FILTER_CHAIN)
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
@EnableWebSecurity
public class WebSecurityEnablerConfiguration {
}

@EnableWebSecurity虽然只是一个注解，但它实际上做了许多事。下面是丛Spring Security官网摘录下来的：

(1) Require authentication to every URL in your application  #在你的应用程序中对每个URL进行验证
(2) Generate a login form for you  #为你生成一个登录表单
(3) Allow the user with the Username user and the Password password to authenticate with form based authentication  #允许使用用户名和密码使用验证表单进行验证
(4) Allow the user to logout  #允许用户登出
(5) CSRF attack prevention  #CSRF attack攻击防范
(6) Session Fixation protection  #Session Fixation Session保护
(7) Security Header integration  #安全Header集成
 - HTTP Strict Transport Security for secure requests  #严格的HTTP传输安全
 - X-Content-Type-Options integration
 - Cache Control (can be overridden later by your application to allow caching of your static resources)
 - X-XSS-Protection integration
 - X-Frame-Options integration to help prevent Clickjacking
(8) Integrate with the following Servlet API methods  #以下Servlet API方法集成
 - HttpServletRequest#getRemoteUser()
 - HttpServletRequest.html#getUserPrincipal()
 - HttpServletRequest.html#isUserInRole(java.lang.String)
 - HttpServletRequest.html#login(java.lang.String, java.lang.String)
 - HttpServletRequest.html#logout()

这么多功能是怎么实现的呢？我们可以查看@EnableWebSecurity的源码，发现该注解会配置3个配置类：

@EnableWebSecurity -> WebSecurityConfiguration.class，WebMvcSecurityConfiguration.class(condition is DispatcherServlet is present)，OAuth2ImportSelector.class(condition is OAuth2ClientConfiguration is present)

@EnableWebSecurity -> @EnableGlobalAuthentication -> AuthenticationConfiguration.class

其中，WebSecurityConfiguration是最主要的配置类。WebMvcSecurityConfiguration，OAuth2ImportSelector这里不再介绍。由于在加载WebSecurityConfiguration的过程中需要用到AuthenticationConfiguration Bean，所以，节下来我们只讲WebSecurityConfiguration。

下面是WebSecurityConfiguration类的源码：

/**
 * Uses a {@link WebSecurity} to create the {@link FilterChainProxy} that performs the web
 * based security for Spring Security. It then exports the necessary beans. Customizations
 * can be made to {@link WebSecurity} by extending {@link WebSecurityConfigurerAdapter}
 * and exposing it as a {@link Configuration} or implementing
 * {@link WebSecurityConfigurer} and exposing it as a {@link Configuration}. This
 * configuration is imported when using {@link EnableWebSecurity}.
 *
 * @see EnableWebSecurity
 * @see WebSecurity
 *
 * @author Rob Winch
 * @author Keesun Baik
 * @since 3.2
 */
@Configuration
public class WebSecurityConfiguration implements ImportAware, BeanClassLoaderAware { }

通过注释可以总结为以下几点：

（1）创建了WebSecurity及上节讲的Security Filter Chain（List<SecurityFilterChain>）的代理对象FilterChainProxy Bean。

（2）创建了其他一些必要的Bean。

（3）如果需要自定义WebSecurity的一些内容，可以继承WebSecurityConfigurerAdapter类或直接实现WebSecurityConfigurer接口，然后在去重写相应方法。当然要用@Configuration声明它为配置类（@EnableWebSecurity中有@Configuration注解，不需要重复添加）。

（A）构建WebSecurity

初始化：WebSecurityConfiguration会先执行一个set方法（通过set方法注入的Bean List<SecurityConfigurer<Filter, WebSecurity>> webSecurityConfigurers）:

@Configuration
public class WebSecurityConfiguration implements ImportAware, BeanClassLoaderAware {

    private List<SecurityConfigurer<Filter, WebSecurity>> webSecurityConfigurers;

    /**
     * Sets the {@code <SecurityConfigurer<FilterChainProxy, WebSecurityBuilder>}
     * instances used to create the web configuration.
     *
     * @param objectPostProcessor the {@link ObjectPostProcessor} used to create a
     * {@link WebSecurity} instance
     * @param webSecurityConfigurers the
     * {@code <SecurityConfigurer<FilterChainProxy, WebSecurityBuilder>} instances used to
     * create the web configuration
     * @throws Exception
     */
    @Autowired(required = false)
    public void setFilterChainProxySecurityConfigurer(
            ObjectPostProcessor<Object> objectPostProcessor,
            @Value("#{@autowiredWebSecurityConfigurersIgnoreParents.getWebSecurityConfigurers()}") List<SecurityConfigurer<Filter, WebSecurity>> webSecurityConfigurers) // [1.2] 
            throws Exception {
        webSecurity = objectPostProcessor
                .postProcess(new WebSecurity(objectPostProcessor)); // [1.4]
        if (debugEnabled != null) {
            webSecurity.debug(debugEnabled);
        }

        Collections.sort(webSecurityConfigurers, AnnotationAwareOrderComparator.INSTANCE);

        Integer previousOrder = null;
        Object previousConfig = null;
        for (SecurityConfigurer<Filter, WebSecurity> config : webSecurityConfigurers) {
            Integer order = AnnotationAwareOrderComparator.lookupOrder(config);
            if (previousOrder != null && previousOrder.equals(order)) {  // [1.3]
                throw new IllegalStateException(
                        "@Order on WebSecurityConfigurers must be unique. Order of "
                                + order + " was already used on " + previousConfig + ", so it cannot be used on "
                                + config + " too.");
            }
            previousOrder = order;
            previousConfig = config;
        }
        for (SecurityConfigurer<Filter, WebSecurity> webSecurityConfigurer : webSecurityConfigurers) {
            webSecurity.apply(webSecurityConfigurer);  // [1.5]
        }
        this.webSecurityConfigurers = webSecurityConfigurers;
    }

    @Bean // [1.1]
    public static AutowiredWebSecurityConfigurersIgnoreParents autowiredWebSecurityConfigurersIgnoreParents(
            ConfigurableListableBeanFactory beanFactory) {
        return new AutowiredWebSecurityConfigurersIgnoreParents(beanFactory);
    }
}

[1.1] 用static先声明一个autowiredWebSecurityConfigurersIgnoreParents Bean。

[1.2] 这个方法先通过@Value注解通过调用[1.1]的AutowiredWebSecurityConfigurersIgnoreParents.getWebSecurityConfigurers()获取ApplicationContext中所有的WebSecurityConfigurer。具体可以看一下AutowiredWebSecurityConfigurersIgnoreParents的源码。

/**
 * A class used to get all the {@link WebSecurityConfigurer} instances from the current
 * {@link ApplicationContext} but ignoring the parent.
 *
 * @author Rob Winch
 *
 */
final class AutowiredWebSecurityConfigurersIgnoreParents {

    private final ConfigurableListableBeanFactory beanFactory;

    public AutowiredWebSecurityConfigurersIgnoreParents(
            ConfigurableListableBeanFactory beanFactory) {
        Assert.notNull(beanFactory, "beanFactory cannot be null");
        this.beanFactory = beanFactory;
    }

    @SuppressWarnings({ "rawtypes", "unchecked" })
    public List<SecurityConfigurer<Filter, WebSecurity>> getWebSecurityConfigurers() {
        List<SecurityConfigurer<Filter, WebSecurity>> webSecurityConfigurers = new ArrayList<SecurityConfigurer<Filter, WebSecurity>>();
        Map<String, WebSecurityConfigurer> beansOfType = beanFactory
                .getBeansOfType(WebSecurityConfigurer.class);
        for (Entry<String, WebSecurityConfigurer> entry : beansOfType.entrySet()) {
            webSecurityConfigurers.add(entry.getValue());
        }
        return webSecurityConfigurers;
    }
}

通常情况下这个WebSecurityConfigurer List只有一个元素，并且就是我们自己继承WebSecurityConfigurerAdapter配置的MySecurityConfig。

@EnableWebSecurity
public class MySecurityConfig extends WebSecurityConfigurerAdapter { }

在SpringBoot自动配置的情况下，如果我们没有继承，则系统默认会使用SpringBootWebSecurityConfiguration的DefaultConfigurerAdapter。

/**
 * The default configuration for web security. It relies on Spring Security's
 * content-negotiation strategy to determine what sort of authentication to use. If the
 * user specifies their own {@link WebSecurityConfigurerAdapter}, this will back-off
 * completely and the users should specify all the bits that they want to configure as
 * part of the custom security configuration.
 *
 * @author Madhura Bhave
 * @since 2.0.0
 */
@ConditionalOnClass(WebSecurityConfigurerAdapter.class) // 有这个对象
@ConditionalOnMissingBean(WebSecurityConfigurerAdapter.class)  // 但是没有声明这个bean
@ConditionalOnWebApplication(type = Type.SERVLET)
public class SpringBootWebSecurityConfiguration {

    @Configuration  // 声明一个DefaultConfigurerAdapter的配置Bean
    @Order(SecurityProperties.BASIC_AUTH_ORDER)
    static class DefaultConfigurerAdapter extends WebSecurityConfigurerAdapter {

    }
}

[1.3] WebSecurityConfigurer如果有多个的情况下，要对他们的@Order进行检查，不能有相同的Order。

[1.4][1.5] 初始化WebSecurity，并将SecurityConfigurer（WebSecurityConfigurerAdapter）应用于此SecurityBuilder（WebSecurity），覆盖完全相同类的任何SecurityConfigurer。

构建：WebSecurity如何被初始化后，就开始构建，下面就是WebSecurityConfiguration中WebSecurity的构建方法，该方法声明为一个Bean，返回的其实就是上一节讲的Spring Security Filter Chain。

    /**
     * Creates the Spring Security Filter Chain
     * @return the {@link Filter} that represents the security filter chain
     * @throws Exception
     */
    @Bean(name = AbstractSecurityWebApplicationInitializer.DEFAULT_FILTER_NAME)
    public Filter springSecurityFilterChain() throws Exception {
        boolean hasConfigurers = webSecurityConfigurers != null
                && !webSecurityConfigurers.isEmpty();
        if (!hasConfigurers) {
            WebSecurityConfigurerAdapter adapter = objectObjectPostProcessor
                    .postProcess(new WebSecurityConfigurerAdapter() {
                    });
            webSecurity.apply(adapter);
        }
        return webSecurity.build();
    }

WebSecurity的构建过程很复杂，大概走了下面几步流程：

[1.1] 调用AbstractSecurityBuilder.build()方法。

[1.2] 调用AbstractConfiguredSecurityBuilder.doBuild()方法（核心方法）。

    @Override
    protected final O doBuild() throws Exception {
        synchronized (configurers) {
            buildState = BuildState.INITIALIZING;

            beforeInit(); // Do nothing if no child class override it.
            init(); // [1.2.1]

            buildState = BuildState.CONFIGURING;

            beforeConfigure();  // Do nothing if no child class override it.
            configure();  // [1.2.2]

            buildState = BuildState.BUILDING;

            O result = performBuild();  // [1.2.3]

            buildState = BuildState.BUILT;

            return result;
        }
    }

[1.2.1] 调用WebSecurityConfigurerAdapter的init(final WebSecurity web)方法。这里构建了HttpSecurity对象，把HttpSecurity添加到WebSecurity的securityFilterChainBuilders中（用于构建过滤器链）以及有一个共享对象FilterSecurityInterceptor。HttpSecurity的构建下面会重点介绍，这里先略过。

    public void init(final WebSecurity web) throws Exception {
        final HttpSecurity http = getHttp();  // 构建HttpSecurity对象
        web.addSecurityFilterChainBuilder(http).postBuildAction(new Runnable() {
        // 把该对象添加到WebSecurity对象中用于接下来[1.2.3]构建过滤器链，可以看下面WebSecurity的
        // addSecurityFilterChainBuilder()方法
            public void run() {
                FilterSecurityInterceptor securityInterceptor = http
                        .getSharedObject(FilterSecurityInterceptor.class);
                web.securityInterceptor(securityInterceptor);
            }
        });
    }

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

    private final List<SecurityBuilder<? extends SecurityFilterChain>> securityFilterChainBuilders = new ArrayList<SecurityBuilder<? extends SecurityFilterChain>>();

    /**
     * <p>
     * Adds builders to create {@link SecurityFilterChain} instances.
     * </p>
     *
     * <p>
     * Typically this method is invoked automatically within the framework from
     * {@link WebSecurityConfigurerAdapter#init(WebSecurity)}
     * </p>
     *
     * @param securityFilterChainBuilder the builder to use to create the
     * {@link SecurityFilterChain} instances
     * @return the {@link WebSecurity} for further customizations
     */
    public WebSecurity addSecurityFilterChainBuilder(
            SecurityBuilder<? extends SecurityFilterChain> securityFilterChainBuilder) {
        this.securityFilterChainBuilders.add(securityFilterChainBuilder);
        return this;
    }
}

[1.2.2] 调用WebSecurityConfigurerAdapter的configure(WebSecurity web)，但是什么都没做。我们可以通过继承WebSecurityConfigurerAdapter来覆盖该方法来自定义配置WebSecurity。

[1.2.3] 调用WebSecurity的performBuild()方法，用[1.2.1]的securityFilterChainBuilders构建过滤器链，并交给FilterChainProxy代理，并返回。值得一说的是，FilterChainProxy最终委托给DelegatingFilterProxy来执行，后者也是web.xml的Security配置项（来源于FilterChainProxy的类注释）。

    @Override
    protected Filter performBuild() throws Exception {
        Assert.state(
                !securityFilterChainBuilders.isEmpty(),
                () -> "At least one SecurityBuilder<? extends SecurityFilterChain> needs to be specified. "
                        + "Typically this done by adding a @Configuration that extends WebSecurityConfigurerAdapter. "
                        + "More advanced users can invoke "
                        + WebSecurity.class.getSimpleName()
                        + ".addSecurityFilterChainBuilder directly");
        int chainSize = ignoredRequests.size() + securityFilterChainBuilders.size();
        List<SecurityFilterChain> securityFilterChains = new ArrayList<>(
                chainSize);
        for (RequestMatcher ignoredRequest : ignoredRequests) {
            securityFilterChains.add(new DefaultSecurityFilterChain(ignoredRequest));
        }
        for (SecurityBuilder<? extends SecurityFilterChain> securityFilterChainBuilder : securityFilterChainBuilders) {
            securityFilterChains.add(securityFilterChainBuilder.build());
        }
        FilterChainProxy filterChainProxy = new FilterChainProxy(securityFilterChains);
        if (httpFirewall != null) {
            filterChainProxy.setFirewall(httpFirewall);
        }
        filterChainProxy.afterPropertiesSet();

        Filter result = filterChainProxy;
        if (debugEnabled) {
            logger.warn("\n\n"
                    + "********************************************************************\n"
                    + "**********        Security debugging is enabled.       *************\n"
                    + "**********    This may include sensitive information.  *************\n"
                    + "**********      Do not use in a production system!     *************\n"
                    + "********************************************************************\n\n");
            result = new DebugFilter(filterChainProxy);
        }
        postBuildAction.run();
        return result;
    }

（B）构建HttpSecurity

在WebSecurity的构建过程中，在调用WebSecurityConfigurerAdapter的init(final WebSecurity web)方法时（见上面的[1.2.1] ），调用WebSecurityConfigurerAdapter的getHttp()构建了HttpSecurity对象。

    protected final HttpSecurity getHttp() throws Exception {
        if (http != null) {
            return http;
        }
        // The default strategy for publishing authentication events
        DefaultAuthenticationEventPublisher eventPublisher = objectPostProcessor
                .postProcess(new DefaultAuthenticationEventPublisher());
        localConfigureAuthenticationBldr.authenticationEventPublisher(eventPublisher);

        AuthenticationManager authenticationManager = authenticationManager(); // [2.1]
        authenticationBuilder.parentAuthenticationManager(authenticationManager);
        authenticationBuilder.authenticationEventPublisher(eventPublisher);
        // 插入一些共享对象（如UserDetailService,ApplicationContext）用于下面HttpSecurity的构建
        Map<Class<? extends Object>, Object> sharedObjects = createSharedObjects();

        http = new HttpSecurity(objectPostProcessor, authenticationBuilder,
                sharedObjects);
        if (!disableDefaults) {
            // @formatter:off
            http
                .csrf().and() // [2.2]
                .addFilter(new WebAsyncManagerIntegrationFilter()) // [2.3]
                .exceptionHandling().and() // [2.4]
                .headers().and() // [2.5]
                .sessionManagement().and() // [2.6]
                .securityContext().and() // [2.7]
                .requestCache().and() // [2.8]
                .anonymous().and() // [2.9]
                .servletApi().and() // [2.10]
                .apply(new DefaultLoginPageConfigurer<>()).and() // [2.11]
                .logout(); // [2.12]
            // @formatter:on
            ClassLoader classLoader = this.context.getClassLoader();
            List<AbstractHttpConfigurer> defaultHttpConfigurers =
                    SpringFactoriesLoader.loadFactories(AbstractHttpConfigurer.class, classLoader);

            for (AbstractHttpConfigurer configurer : defaultHttpConfigurers) {
                http.apply(configurer);
            }
        }
        configure(http);
        return http;
    }

    protected void configure(HttpSecurity http) throws Exception {
        logger.debug("Using default configure(HttpSecurity). If subclassed this will potentially override subclass configure(HttpSecurity).");

        http
            .authorizeRequests() // [2.13]
                .anyRequest().authenticated()
                .and()
            .formLogin().and() // [2.14]
            .httpBasic(); // [2.15]
    }

[2.1] 这里实际上使用了配置类AuthenticationConfiguration Bean得到了一个AuthenticationManager，这个过程中，系统会自动配置这些认证对象：

ProviderManager -> AuthenticationManager

DaoAuthenticationProvider -> AuthenticationProvider

InMemoryUserDetailsManager -> UserDetailsService

User -> MutableUser -> MutableUserDetails -> UserDetails

其中，MutableUser代理了User对象及一个临时的password。系统会自动生成1个MutableUser，name为user（无ROLE）。

具体细节可以看（C）部分。

[2.2] 添加配置器CsrfConfigurer（包含过滤器CsrfFilter *）对CSRF的支持。

[2.3] 添加过滤器WebAsyncManagerIntegrationFilter。

[2.4] 添加配置器ExceptionHandlingConfigurer（包含过滤器ExceptionTranslationFilter *）对异常处理的支持。

[2.5] 添加配置器HeadersConfigurer（包含过滤器HeaderWriterFilter *）支持Adds the Security HTTP headers to the response。

[2.6] 添加配置器SessionManagementConfigurer（包含过滤器SessionManagementFilter *）支持session管理。

[2.7] 添加配置器SecurityContextConfigurer（包含过滤器SecurityContextPersistenceFilter *）支持对SecurityContextHolder的配置。

[2.8] 添加配置器RequestCacheConfigurer（包含过滤器RequestCacheAwareFilter *）支持request cache。

[2.9] 添加配置器AnonymousConfigurer（包含过滤器AnonymousAuthenticationFilter *）支持Anonymous authentication。

[2.10] 添加配置器ServletApiConfigurer（包含过滤器SecurityContextHolderAwareRequestFilter *）支持更多Servlet API。

[2.11] 添加配置器DefaultLoginPageConfigurer（包含过滤器DefaultLoginPageGeneratingFilter，DefaultLogoutPageGeneratingFilter *）支持默认的login和logout。

[2.12] 添加配置器LogoutConfigurer（包含过滤器LogoutFilter *）支持logout。

[2.13] 添加配置器ExpressionUrlAuthorizationConfigurer -> AbstractInterceptUrlConfigurer（包含过滤器FilterSecurityInterceptor *）支持URL based authorization。

[2.14] 添加配置器FormLoginConfigurer -> AbstractAuthenticationFilterConfigurer（包含过滤器UsernamePasswordAuthenticationFilter *）支持通过login认证。

[2.15] 添加配置器HttpBasicConfigurer（包含过滤器BasicAuthenticationFilter *）支持HTTP basic based authentication。

[*] 该过滤器在[1.2.3]中securityFilterChainBuilder.build()时通过调用该配置器的configure()方法把过滤器加到HttpSecurity中。

以上的15个过滤器就和章节2Spring Security(2)：过滤器链（filter chain）的介绍中的15个过滤器一一对应。

（C）构建AuthenticationManager及自动配置时自动创建认证对象

由[2.1]可知，Spring Security会自动创建一些认证对象。那么它们是怎么创建出来的呢？

在[2.1]中，调用了WebSecurityConfigurerAdapter.authenticationManager()方法。从下面的代码可以看到，由于我们并未配置自定义的AuthenticationManagerBuilder（变量名是localConfigureAuthenticationBldr），所以我们用注入的AuthenticationConfiguration，调用AuthenticationConfiguration的getAuthenticationManager()方法，得到了AuthenticationManager对象。

WebSecurityConfigurerAdapter.authenticationManager()：

    private AuthenticationConfiguration authenticationConfiguration;

    /**
     * Gets the {@link AuthenticationManager} to use. The default strategy is if
     * {@link #configure(AuthenticationManagerBuilder)} method is overridden to use the
     * {@link AuthenticationManagerBuilder} that was passed in. Otherwise, autowire the
     * {@link AuthenticationManager} by type.
     *
     * @return the {@link AuthenticationManager} to use
     * @throws Exception
     */
    protected AuthenticationManager authenticationManager() throws Exception {
        if (!authenticationManagerInitialized) {
            configure(localConfigureAuthenticationBldr);
            if (disableLocalConfigureAuthenticationBldr) {
                authenticationManager = authenticationConfiguration
                        .getAuthenticationManager(); // execute here
            }
            else {
                authenticationManager = localConfigureAuthenticationBldr.build();
            }
            authenticationManagerInitialized = true;
        }
        return authenticationManager;
    }

    @Autowired
    public void setAuthenticationConfiguration(
            AuthenticationConfiguration authenticationConfiguration) {
        this.authenticationConfiguration = authenticationConfiguration;
    }

AuthenticationConfiguration.getAuthenticationManager()：

    public AuthenticationManager getAuthenticationManager() throws Exception {
        if (this.authenticationManagerInitialized) {
            return this.authenticationManager;
        }
        // [3.1]
        AuthenticationManagerBuilder authBuilder = authenticationManagerBuilder(
                this.objectPostProcessor, this.applicationContext);
        if (this.buildingAuthenticationManager.getAndSet(true)) {
            return new AuthenticationManagerDelegator(authBuilder);
        }

        // [3.2]
        for (GlobalAuthenticationConfigurerAdapter config : globalAuthConfigurers) {
            authBuilder.apply(config);
        }

        // [3.3]
        authenticationManager = authBuilder.build();

        if (authenticationManager == null) {
            authenticationManager = getAuthenticationManagerBean();
        }

        this.authenticationManagerInitialized = true;
        return authenticationManager;
    }

[3.1] 调用AuthenticationConfiguration.authenticationManagerBuilder()方法，使用了一个默认的AuthenticationManagerBuilder实现类DefaultPasswordEncoderAuthenticationManagerBuilder（同时这也是一个Bean）。

    @Bean
    public AuthenticationManagerBuilder authenticationManagerBuilder(
            ObjectPostProcessor<Object> objectPostProcessor, ApplicationContext context) {
        LazyPasswordEncoder defaultPasswordEncoder = new LazyPasswordEncoder(context);
        AuthenticationEventPublisher authenticationEventPublisher = getBeanOrNull(context, AuthenticationEventPublisher.class);

        DefaultPasswordEncoderAuthenticationManagerBuilder result = new DefaultPasswordEncoderAuthenticationManagerBuilder(objectPostProcessor, defaultPasswordEncoder);
        if (authenticationEventPublisher != null) {
            result.authenticationEventPublisher(authenticationEventPublisher);
        }
        return result;
    }

[3.2] 这个globalAuthConfigurers其实就是AuthenticationConfiguration中声明的3个static bean。由于是static的，所以最早加载。

    @Bean
    public static GlobalAuthenticationConfigurerAdapter enableGlobalAuthenticationAutowiredConfigurer(
            ApplicationContext context) {return new EnableGlobalAuthenticationAutowiredConfigurer(context);
    }

    @Bean
    public static InitializeUserDetailsBeanManagerConfigurer initializeUserDetailsBeanManagerConfigurer(ApplicationContext context) {return new InitializeUserDetailsBeanManagerConfigurer(context);
    }

    @Bean
    public static InitializeAuthenticationProviderBeanManagerConfigurer initializeAuthenticationProviderBeanManagerConfigurer(ApplicationContext context) {return new InitializeAuthenticationProviderBeanManagerConfigurer(context);
    }

[3.3] build()方法会调用AbstractConfiguredSecurityBuilder.doBuild()方法，最终会先后调用[3.2]的3个configurer的init()方法和configure()方法，及调用[3.1]DefaultPasswordEncoderAuthenticationManagerBuilder的父类AuthenticationManagerBuilder的performBuild()方法。

    @Override
    protected final O doBuild() throws Exception {
        synchronized (configurers) {
            buildState = BuildState.INITIALIZING;

            beforeInit();
            // 循环调用[3.2]的3个configurer的init()方法（有些可能没有）
            init();

            buildState = BuildState.CONFIGURING;

            beforeConfigure();
            // 循环调用[3.2]的3个configurer的configure()方法（有些可能没有）
            configure();

            buildState = BuildState.BUILDING;
            // 调用[3.1]DefaultPasswordEncoderAuthenticationManagerBuilder的父类AuthenticationManagerBuilder的performBuild()方法
            O result = performBuild();

            buildState = BuildState.BUILT;

            return result;
        }
    }

通过调用这些方法自动生成了：

ProviderManager -> AuthenticationManager

DaoAuthenticationProvider -> AuthenticationProvider

InMemoryUserDetailsManager -> UserDetailsService

User -> MutableUser -> MutableUserDetails -> UserDetails

（C.1）User & InMemoryUserDetailsManager & DaoAuthenticationProvider：在InitializeUserDetailsBeanManagerConfigurer.config()中，及自动配置类UserDetailsServiceAutoConfiguration中创建

InitializeUserDetailsBeanManagerConfigurer：

        @Override
        public void configure(AuthenticationManagerBuilder auth) throws Exception {
            if (auth.isConfigured()) {
                return;
            }
            // 如果使用了Spring Boot, 执行这一步时会使用自动配置，
            // 从UserDetailsServiceAutoConfiguration中Lazy load一个InMemoryUserDetailsManager
            UserDetailsService userDetailsService = getBeanOrNull(
                    UserDetailsService.class);
            if (userDetailsService == null) {
                return;
            }

            PasswordEncoder passwordEncoder = getBeanOrNull(PasswordEncoder.class);
            UserDetailsPasswordService passwordManager = getBeanOrNull(UserDetailsPasswordService.class);
            // 创建DaoAuthenticationProvider，并把UserDetailsService放入其中
            DaoAuthenticationProvider provider = new DaoAuthenticationProvider();
            provider.setUserDetailsService(userDetailsService);
            if (passwordEncoder != null) {
                provider.setPasswordEncoder(passwordEncoder);
            }
            if (passwordManager != null) {
                provider.setUserDetailsPasswordService(passwordManager);
            }
            provider.afterPropertiesSet();

            auth.authenticationProvider(provider);
        }

UserDetailsServiceAutoConfiguration：需要注意的是，Spring Bean容器中，如果同时没有AuthenticationManager，AuthenticationProvider，UserDetailsService时，该自动配置才会生效。（To also switch off the UserDetailsService configuration, you can add a bean of type UserDetailsService, AuthenticationProvider, or AuthenticationManager.）

@Configuration
@ConditionalOnClass(AuthenticationManager.class)
@ConditionalOnBean(ObjectPostProcessor.class)
@ConditionalOnMissingBean({ AuthenticationManager.class, AuthenticationProvider.class,
        UserDetailsService.class })
public class UserDetailsServiceAutoConfiguration {

    private static final String NOOP_PASSWORD_PREFIX = "{noop}";

    private static final Pattern PASSWORD_ALGORITHM_PATTERN = Pattern
            .compile("^\\{.+}.*$");

    private static final Log logger = LogFactory
            .getLog(UserDetailsServiceAutoConfiguration.class);

    @Bean
    @ConditionalOnMissingBean(type = "org.springframework.security.oauth2.client.registration.ClientRegistrationRepository")
    @Lazy
    public InMemoryUserDetailsManager inMemoryUserDetailsManager(
            SecurityProperties properties,
            ObjectProvider<PasswordEncoder> passwordEncoder) {
        SecurityProperties.User user = properties.getUser();
        List<String> roles = user.getRoles();
        return new InMemoryUserDetailsManager(User.withUsername(user.getName())
                .password(getOrDeducePassword(user, passwordEncoder.getIfAvailable()))
                .roles(StringUtils.toStringArray(roles)).build());
    }

    private String getOrDeducePassword(SecurityProperties.User user,
            PasswordEncoder encoder) {
        String password = user.getPassword();
        if (user.isPasswordGenerated()) {
            logger.info(String.format("%n%nUsing generated security password: %s%n",
                    user.getPassword()));
        }
        if (encoder != null || PASSWORD_ALGORITHM_PATTERN.matcher(password).matches()) {
            return password;
        }
        return NOOP_PASSWORD_PREFIX + password;
    }

}

（C.2）ProviderManager ：在AuthenticationManagerBuilder.performBuild()中创建

    @Override
    protected ProviderManager performBuild() throws Exception {
        if (!isConfigured()) {
            logger.debug("No authenticationProviders and no parentAuthenticationManager defined. Returning null.");
            return null;
        }
        ProviderManager providerManager = new ProviderManager(authenticationProviders,
                parentAuthenticationManager);
        if (eraseCredentials != null) {
            providerManager.setEraseCredentialsAfterAuthentication(eraseCredentials);
        }
        if (eventPublisher != null) {
            providerManager.setAuthenticationEventPublisher(eventPublisher);
        }
        providerManager = postProcess(providerManager);
        return providerManager;
    }

 总结：

最后上两张类图，分别是SecurityBuilder和SecurityConfiger。流程实际上就是先调用Builder的add()方法或apply()方法添加和维护一个SecurityConfiger List。最后通过调用Builder的build()方法（实际上是AbstractConfiguredSecurityBuilder的doBuild()方法），调用SecurityConfiger的init()方法和configure()方法构建WebSecurity及过滤器链。