初识

Spring Security是通过SecuriyFilterChains过滤器链来保证应用安全的，而这些过滤器链由FilterChainProxy（本质上是个Filter）来管理，每个uri都对应一个SecurityFilterChain，即对应SecurityFilterChain中的Filters。

FilterChainProxy中由SecurityFilterChain维护了很多Filter，debug进入可以看到：

image

SpringSecurity的密码登录就是由UsernamePasswordAuthenticationFilter过滤器来实现的，先上一张登录校验流程图：

spring-security-login

UsernamePasswordAuthenticationFilter

UsernamePasswordAuthenticationFilter 继承了 AbstractAuthenticationProcessingFilter，doFilter()方法由其父类实现。

image

public Authentication attemptAuthentication(HttpServletRequest request,
            HttpServletResponse response) throws AuthenticationException {
    // 判断请求方式
    if (postOnly && !request.getMethod().equals("POST")) {
        throw new AuthenticationServiceException(
            "Authentication method not supported: " + request.getMethod());
    }

    // 获取用户名密码
    String username = obtainUsername(request);
    String password = obtainPassword(request);

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

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

    username = username.trim();

    // 使用用户名密码生成token
    UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(
        username, password);

    // Allow subclasses to set the "details" property
    setDetails(request, authRequest);

    // 根据token，匹配合适的provider认证
    return this.getAuthenticationManager().authenticate(authRequest);
}

ProviderManager

ProviderManager#authenticate() 会获取所有的AuthenticationProvider，然后遍历，找出与封装的 Token 匹配的 Provider，调用其 authenticate()方法。

public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
    Class<? extends Authentication> toTest = authentication.getClass();
    AuthenticationException lastException = null;
    AuthenticationException parentException = null;
    Authentication result = null;
    Authentication parentResult = null;
    boolean debug = logger.isDebugEnabled();

    for (AuthenticationProvider provider : getProviders()) {
        // 遍历所有Providers，找到与token相匹配的provider
        if (!provider.supports(toTest)) {
            continue;
        }

        if (debug) {
            logger.debug("Authentication attempt using "
                         + provider.getClass().getName());
        }

        try {
            // 调用authenticate方法认证，拿到认证结果
            result = provider.authenticate(authentication);

            if (result != null) {
                copyDetails(authentication, result);
                break;
            }
        }
        catch (AccountStatusException | InternalAuthenticationServiceException e) {
            prepareException(e, authentication);
            // SEC-546: Avoid polling additional providers if auth failure is due to
            // invalid account status
            throw e;
        } catch (AuthenticationException e) {
            lastException = e;
        }
    }

    if (result == null && parent != null) {
        // Allow the parent to try.
        try {
            result = parentResult = 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 = parentException = e;
        }
    }

    if (result != null) {
        if (eraseCredentialsAfterAuthentication
            && (result instanceof CredentialsContainer)) {
            // 认证完成，移除密码等敏感信息
            // Authentication is complete. Remove credentials and other secret data
            // from authentication
            ((CredentialsContainer) result).eraseCredentials();
        }

        // If the parent AuthenticationManager was attempted and successful than it will publish an AuthenticationSuccessEvent
        // This check prevents a duplicate AuthenticationSuccessEvent if the parent AuthenticationManager already published it
        if (parentResult == null) {
            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}"));
    }

    // If the parent AuthenticationManager was attempted and failed than it will publish an AbstractAuthenticationFailureEvent
    // This check prevents a duplicate AbstractAuthenticationFailureEvent if the parent AuthenticationManager already published it
    if (parentException == null) {
        prepareException(lastException, authentication);
    }

    throw lastException;
}

provider.supports方法，以token（authentication）的类型为标准，判断是否是UsernamePasswordAuthenticationToken类或其子类，为扩展UsernamePasswordAuthenticationToken提供了基础。

public boolean supports(Class<?> authentication) {
    return (UsernamePasswordAuthenticationToken.class
            .isAssignableFrom(authentication));
}

认证完成后，还会调用eraseCredentials()方法，进行密码擦除工作，比如把密码置空。

AbstractUserDetailsAuthenticationProvider

ProviderManager#authenticate() 方法，进入AbstractUserDetailsAuthenticationProvider 的 authenticate 方法。

public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
    // 支持多语言的信息提示
    Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication,
                        () -> messages.getMessage(
                            "AbstractUserDetailsAuthenticationProvider.onlySupports",
                            "Only UsernamePasswordAuthenticationToken is supported"));

    // 获取用户名
    // Determine username
    String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED"
        : authentication.getName();

    // 先从缓存中获取UserDetails
    boolean cacheWasUsed = true;
    UserDetails user = this.userCache.getUserFromCache(username);

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

        try {
            // 获取UserDetails
            user = retrieveUser(username,
                                (UsernamePasswordAuthenticationToken) authentication);
        }
        catch (UsernameNotFoundException notFound) {
            logger.debug("User '" + username + "' not found");

            if (hideUserNotFoundExceptions) {
                // 隐藏用户不存在异常，统一抛出BadCredentialsException
                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 {
        // 用户状态前置校验：账户锁定、不可用、过期
        preAuthenticationChecks.check(user);
        // 这里主要是校验密码是否正确
        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;
        }
    }

    // 用户状态后置校验：账户密码过期
    postAuthenticationChecks.check(user);

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

    Object principalToReturn = user;

    if (forcePrincipalAsString) {
        principalToReturn = user.getUsername();
    }

    return createSuccessAuthentication(principalToReturn, authentication, user);
}

重点关注获取用户信息retrieveUser()和密码校验additionalAuthenticationChecks()方法，他们都是抽象方法，由其子类 DaoAuthenticationProvider 实现。

DaoAuthenticationProvider

retrieveUser()

protected final UserDetails retrieveUser(String username,
            UsernamePasswordAuthenticationToken authentication)
            throws AuthenticationException {
    prepareTimingAttackProtection();
    try {
        // 根据username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);
    }
}

最终调用了 UserDetailsService 的 loadUserByUsername()方法，来获取用户信息，我们可以实现 UserDetailsService 接口，从数据库中查出用户的信息。

additionalAuthenticationChecks()

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();

    // 校验密码是否相同
    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"));
    }
}

使用了passwordEncoder.matches()方法来匹配密码是否相同。

总结

最后再看下这张流程图，就比较清晰了

spring-security-login.png

可以留言说下你学习源码的感受，你的评论、在看、转发，都能让我高兴好久。