Spring Security 进阶-原理篇

摘要：过滤器基本都是通过过滤器来完成配置的身份认证权限认证以及登出。密码比对通过进行密码比对注可自定义通过获取通过获取生成身份认证通过后最终返回的记录认证的身份信息

知彼知己方能百战百胜，用 Spring Security 来满足我们的需求最好了解其原理，这样才能随意拓展，本篇文章主要记录 Spring Security 的基本运行流程。

Spring Security 基本都是通过过滤器来完成配置的身份认证、权限认证以及登出。

Spring Security 在 Servlet 的过滤链（filter chain）中注册了一个过滤器 FilterChainProxy，它会把请求代理到 Spring Security 自己维护的多个过滤链，每个过滤链会匹配一些 URL，如果匹配则执行对应的过滤器。过滤链是有顺序的，一个请求只会执行第一条匹配的过滤链。Spring Security 的配置本质上就是新增、删除、修改过滤器。

默认情况下系统帮我们注入的这 15 个过滤器，分别对应配置不同的需求。接下来我们重点是分析下 UsernamePasswordAuthenticationFilter 这个过滤器，他是用来使用用户名和密码登录认证的过滤器，但是很多情况下我们的登录不止是简单的用户名和密码，又可能是用到第三方授权登录，这个时候我们就需要使用自定义过滤器，当然这里不做详细说明，只是说下自定义过滤器怎么注入。

@Override
protected void configure(HttpSecurity http) throws Exception {
    
    http.addFilterAfter(...);
    ...
 }

在开始身份认证流程之前我们需要了解下几个基本概念

SecurityContextHolder 存储 SecurityContext 对象。SecurityContextHolder 是一个存储代理，有三种存储模式分别是：

MODE_THREADLOCAL：SecurityContext 存储在线程中。

MODE_INHERITABLETHREADLOCAL：SecurityContext 存储在线程中，但子线程可以获取到父线程中的 SecurityContext。

MODE_GLOBAL：SecurityContext 在所有线程中都相同。

SecurityContextHolder 默认使用 MODE_THREADLOCAL 模式，SecurityContext 存储在当前线程中。调用 SecurityContextHolder 时不需要显示的参数传递，在当前线程中可以直接获取到 SecurityContextHolder 对象。

//获取当前线程里面认证的对象
SecurityContext context = SecurityContextHolder.getContext();
Authentication authentication = context.getAuthentication();

//保存认证对象 (一般用于自定义认证成功保存认证对象)
SecurityContextHolder.getContext().setAuthentication(authResult);

//清空认证对象 (一般用于自定义登出清空认证对象)
SecurityContextHolder.clearContext();

Authentication 即验证，表明当前用户是谁。什么是验证，比如一组用户名和密码就是验证，当然错误的用户名和密码也是验证，只不过 Spring Security 会校验失败。

Authentication 接口

public interface Authentication extends Principal, Serializable {
       //获取用户权限，一般情况下获取到的是用户的角色信息
       Collection getAuthorities();
       //获取证明用户认证的信息，通常情况下获取到的是密码等信息，不过登录成功就会被移除
       Object getCredentials();
       //获取用户的额外信息，比如 IP 地址、经纬度等
       Object getDetails();
       //获取用户身份信息，在未认证的情况下获取到的是用户名，在已认证的情况下获取到的是 UserDetails (暂时理解为，当前应用用户对象的扩展)
       Object getPrincipal();
       //获取当前 Authentication 是否已认证
       boolean isAuthenticated();
       //设置当前 Authentication 是否已认证
       void setAuthenticated(boolean isAuthenticated);
}

其实这三者很好区分，AuthenticationManager 主要就是为了完成身份认证流程，ProviderManager 是 AuthenticationManager 接口的具体实现类，ProviderManager 里面有个记录 AuthenticationProvider 对象的集合属性 providers，AuthenticationProvider 接口类里有两个方法

public interface AuthenticationProvider {
    //实现具体的身份认证逻辑，认证失败抛出对应的异常
    Authentication authenticate(Authentication authentication)
            throws AuthenticationException;
    //该认证类是否支持该 Authentication 的认证
    boolean supports(Class authentication);
}

接下来就是遍历 ProviderManager 里面的 providers 集合，找到和合适的 AuthenticationProvider 完成身份认证。

在 UserDetailsService 接口中只有一个简单的方法

public interface UserDetailsService {
    //根据用户名查到对应的 UserDetails 对象
    UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;
}

对于上面概念有什么不明白的地方，在们在接下来的流程中慢慢分析

在运行到 UsernamePasswordAuthenticationFilter 过滤器的时候首先是进入其父类 AbstractAuthenticationProcessingFilter 的 doFilter() 方法中

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
        throws IOException, ServletException {
    ...
    //首先配对是不是配置的身份认证的URI,是则执行下面的认证,不是则跳过
    if (!requiresAuthentication(request, response)) {
        chain.doFilter(request, response);

        return;
    }
    ...
    Authentication authResult;

    try {
        //关键方法, 实现认证逻辑并返回 Authentication, 由其子类 UsernamePasswordAuthenticationFilter 实现, 由下面 5.3 详解
        authResult = attemptAuthentication(request, response);
        if (authResult == null) {
            // return immediately as subclass has indicated that it hasn"t completed
            // authentication
            return;
        }
        sessionStrategy.onAuthentication(authResult, request, response);
    }
    catch (InternalAuthenticationServiceException failed) {
        //认证失败调用...由下面 5.1 详解
        unsuccessfulAuthentication(request, response, failed);

        return;
    }
    catch (AuthenticationException failed) {
        //认证失败调用...由下面 5.1 详解
        unsuccessfulAuthentication(request, response, failed);

        return;
    }

    // Authentication success
    if (continueChainBeforeSuccessfulAuthentication) {
        chain.doFilter(request, response);
    }
    //认证成功调用...由下面 5.2 详解
    successfulAuthentication(request, response, chain, authResult);
}

protected void unsuccessfulAuthentication(HttpServletRequest request,
                                          HttpServletResponse response, AuthenticationException failed)
        throws IOException, ServletException {
    SecurityContextHolder.clearContext();
    ...
    rememberMeServices.loginFail(request, response);
    //该 handler 处理失败界面跳转和响应逻辑
    failureHandler.onAuthenticationFailure(request, response, failed);
}

这里默认配置的失败处理 handler 是 SimpleUrlAuthenticationFailureHandler，可自定义。

public class SimpleUrlAuthenticationFailureHandler implements
        AuthenticationFailureHandler {
    ...

    public void onAuthenticationFailure(HttpServletRequest request,
            HttpServletResponse response, AuthenticationException exception)
            throws IOException, ServletException {
        //没有配置失败跳转的URL则直接响应错误
        if (defaultFailureUrl == null) {
            logger.debug("No failure URL set, sending 401 Unauthorized error");

            response.sendError(HttpStatus.UNAUTHORIZED.value(),
                HttpStatus.UNAUTHORIZED.getReasonPhrase());
        }
        else {
            //否则
            //缓存异常
            saveException(request, exception);
            //根据配置的异常页面是重定向还是转发进行不同方式跳转
            if (forwardToDestination) {
                logger.debug("Forwarding to " + defaultFailureUrl);

                request.getRequestDispatcher(defaultFailureUrl)
                        .forward(request, response);
            }
            else {
                logger.debug("Redirecting to " + defaultFailureUrl);
                redirectStrategy.sendRedirect(request, response, defaultFailureUrl);
            }
        }
    }
    //缓存异常,转发则保存在request里面,重定向则保存在session里面
    protected final void saveException(HttpServletRequest request,
            AuthenticationException exception) {
        if (forwardToDestination) {
            request.setAttribute(WebAttributes.AUTHENTICATION_EXCEPTION, exception);
        }
        else {
            HttpSession session = request.getSession(false);

            if (session != null || allowSessionCreation) {
                request.getSession().setAttribute(WebAttributes.AUTHENTICATION_EXCEPTION,
                        exception);
            }
        }
    }
}

这里做下小拓展：用系统的错误处理handler，指定认证失败跳转的URL，在MVC里面对应的URL方法里面可以通过key从request或session里面拿到错误信息，反馈给前端

protected void successfulAuthentication(HttpServletRequest request,
                                        HttpServletResponse response, FilterChain chain, Authentication authResult)
        throws IOException, ServletException {
    ...
    //这里要注意很重要，将认证完成返回的 Authentication 保存到线程对应的 `SecurityContext` 中
    SecurityContextHolder.getContext().setAuthentication(authResult);

    rememberMeServices.loginSuccess(request, response, authResult);

    // Fire event
    if (this.eventPublisher != null) {
        eventPublisher.publishEvent(new InteractiveAuthenticationSuccessEvent(
                authResult, this.getClass()));
    }
    //该 handler 就是为了完成页面跳转
    successHandler.onAuthenticationSuccess(request, response, authResult);
}

这里默认配置的成功处理 handler 是 SavedRequestAwareAuthenticationSuccessHandler，里面的代码就不做具体展开了，反正是跳转到指定的认证成功之后的界面，可自定义。

public class UsernamePasswordAuthenticationFilter extends
        AbstractAuthenticationProcessingFilter {
    ...
    public static final String SPRING_SECURITY_FORM_USERNAME_KEY = "username";
    public static final String SPRING_SECURITY_FORM_PASSWORD_KEY = "password";

    private String usernameParameter = SPRING_SECURITY_FORM_USERNAME_KEY;
    private String passwordParameter = SPRING_SECURITY_FORM_PASSWORD_KEY;
    private boolean postOnly = true;

    ...
    //开始身份认证逻辑
    public Authentication attemptAuthentication(HttpServletRequest request,
            HttpServletResponse response) throws AuthenticationException {
        if (postOnly && !request.getMethod().equals("POST")) {
            throw new AuthenticationServiceException(
                    "Authentication method not supported: " + request.getMethod());
        }

        String username = obtainUsername(request);
        String password = obtainPassword(request);

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

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

        username = username.trim();
        //先用前端提交过来的 username 和 password 封装一个简易的 AuthenticationToken
        UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(
                username, password);

        // Allow subclasses to set the "details" property
        setDetails(request, authRequest);
        //具体的认证逻辑还是交给 AuthenticationManager 对象的 authenticate(..) 方法完成,接着往下看
        return this.getAuthenticationManager().authenticate(authRequest);
    }
}

由源码断点跟踪得知，最终解析是由 AuthenticationManager 接口实现类 ProviderManager 来完成

public class ProviderManager implements AuthenticationManager, MessageSourceAware,
        InitializingBean {
    ...
    private List providers = Collections.emptyList();
    ...
    
    public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
        ....
        //遍历所有的 AuthenticationProvider, 找到合适的完成身份验证
        for (AuthenticationProvider provider : getProviders()) {
            if (!provider.supports(toTest)) {
                continue;
            }
            ...
            try {
                //进行具体的身份验证逻辑, 这里使用到的是 DaoAuthenticationProvider, 具体逻辑记着往下看
                result = provider.authenticate(authentication);

                if (result != null) {
                    copyDetails(authentication, result);
                    break;
                }
            }
            catch 
            ...
        }
        ...
        throw lastException;
    }
}

DaoAuthenticationProvider 继承自 AbstractUserDetailsAuthenticationProvider 实现了 AuthenticationProvider 接口

public abstract class AbstractUserDetailsAuthenticationProvider implements
        AuthenticationProvider, InitializingBean, MessageSourceAware {
    ...
    private UserDetailsChecker preAuthenticationChecks = new DefaultPreAuthenticationChecks();
    private UserDetailsChecker postAuthenticationChecks = new DefaultPostAuthenticationChecks();
    ...

    public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
        ...
        // 获得提交过来的用户名
        String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED"
                : authentication.getName();
        //根据用户名从缓存中查找 UserDetails
        boolean cacheWasUsed = true;
        UserDetails user = this.userCache.getUserFromCache(username);

        if (user == null) {
            cacheWasUsed = false;

            try {
                //缓存中没有则通过 retrieveUser(..) 方法查找 (看下面 DaoAuthenticationProvider 的实现)
                user = retrieveUser(username,
                        (UsernamePasswordAuthenticationToken) authentication);
            }
            catch 
            ...
        }

        try {
            //比对前的检查,例如账户以一些状态信息(是否锁定, 过期...)
            preAuthenticationChecks.check(user);
            //子类实现比对规则 (看下面 DaoAuthenticationProvider 的实现)
            additionalAuthenticationChecks(user,
                    (UsernamePasswordAuthenticationToken) authentication);
        }
        catch (AuthenticationException exception) {
            if (cacheWasUsed) {
                // There was a problem, so try again after checking
                // we"re using latest data (i.e. not from the cache)
                cacheWasUsed = false;
                user = retrieveUser(username,
                        (UsernamePasswordAuthenticationToken) authentication);
                preAuthenticationChecks.check(user);
                additionalAuthenticationChecks(user,
                        (UsernamePasswordAuthenticationToken) authentication);
            }
            else {
                throw exception;
            }
        }

        postAuthenticationChecks.check(user);

        if (!cacheWasUsed) {
            this.userCache.putUserInCache(user);
        }

        Object principalToReturn = user;

        if (forcePrincipalAsString) {
            principalToReturn = user.getUsername();
        }
        //根据最终user的一些信息重新生成具体详细的 Authentication 对象并返回 
        return createSuccessAuthentication(principalToReturn, authentication, user);
    }
    //具体生成还是看子类实现
    protected Authentication createSuccessAuthentication(Object principal,
            Authentication authentication, UserDetails user) {
        // Ensure we return the original credentials the user supplied,
        // so subsequent attempts are successful even with encoded passwords.
        // Also ensure we return the original getDetails(), so that future
        // authentication events after cache expiry contain the details
        UsernamePasswordAuthenticationToken result = new UsernamePasswordAuthenticationToken(
                principal, authentication.getCredentials(),
                authoritiesMapper.mapAuthorities(user.getAuthorities()));
        result.setDetails(authentication.getDetails());

        return result;
    }
}

接下来我们来看下 DaoAuthenticationProvider 里面的三个重要的方法，比对方式、获取需要比对的 UserDetails 对象以及生产最终返回 Authentication 的方法。

public class DaoAuthenticationProvider extends AbstractUserDetailsAuthenticationProvider {
    ...
    //密码比对
    @SuppressWarnings("deprecation")
    protected void additionalAuthenticationChecks(UserDetails userDetails,
            UsernamePasswordAuthenticationToken authentication)
            throws AuthenticationException {
        if (authentication.getCredentials() == null) {
            logger.debug("Authentication failed: no credentials provided");

            throw new BadCredentialsException(messages.getMessage(
                    "AbstractUserDetailsAuthenticationProvider.badCredentials",
                    "Bad credentials"));
        }

        String presentedPassword = authentication.getCredentials().toString();
        //通过 PasswordEncoder 进行密码比对, 注: 可自定义
        if (!passwordEncoder.matches(presentedPassword, userDetails.getPassword())) {
            logger.debug("Authentication failed: password does not match stored value");

            throw new BadCredentialsException(messages.getMessage(
                    "AbstractUserDetailsAuthenticationProvider.badCredentials",
                    "Bad credentials"));
        }
    }

    //通过 UserDetailsService 获取 UserDetails
    protected final UserDetails retrieveUser(String username,
            UsernamePasswordAuthenticationToken authentication)
            throws AuthenticationException {
        prepareTimingAttackProtection();
        try {
            //通过 UserDetailsService 获取 UserDetails
            UserDetails loadedUser = this.getUserDetailsService().loadUserByUsername(username);
            if (loadedUser == null) {
                throw new InternalAuthenticationServiceException(
                        "UserDetailsService returned null, which is an interface contract violation");
            }
            return loadedUser;
        }
        catch (UsernameNotFoundException ex) {
            mitigateAgainstTimingAttack(authentication);
            throw ex;
        }
        catch (InternalAuthenticationServiceException ex) {
            throw ex;
        }
        catch (Exception ex) {
            throw new InternalAuthenticationServiceException(ex.getMessage(), ex);
        }
    }

    //生成身份认证通过后最终返回的 Authentication, 记录认证的身份信息
    @Override
    protected Authentication createSuccessAuthentication(Object principal,
            Authentication authentication, UserDetails user) {
        boolean upgradeEncoding = this.userDetailsPasswordService != null
                && this.passwordEncoder.upgradeEncoding(user.getPassword());
        if (upgradeEncoding) {
            String presentedPassword = authentication.getCredentials().toString();
            String newPassword = this.passwordEncoder.encode(presentedPassword);
            user = this.userDetailsPasswordService.updatePassword(user, newPassword);
        }
        return super.createSuccessAuthentication(principal, authentication, user);
    }
}