摘要：過濾器基本都是通過過濾器來完成配置的身份認證權限認證以及登出。密碼比對通過進行密碼比對注可自定義通過獲取通過獲取生成身份認證通過后最終返回的記錄認證的身份信息

知彼知己方能百戰百勝，用 Spring Security 來滿足我們的需求最好了解其原理，這樣才能隨意拓展，本篇文章主要記錄 Spring Security 的基本運行流程。

Spring Security 基本都是通過過濾器來完成配置的身份認證、權限認證以及登出。

Spring Security 在 Servlet 的過濾鏈（filter chain）中注冊了一個過濾器 FilterChainProxy，它會把請求代理到 Spring Security 自己維護的多個過濾鏈，每個過濾鏈會匹配一些 URL，如果匹配則執行對應的過濾器。過濾鏈是有順序的，一個請求只會執行第一條匹配的過濾鏈。Spring Security 的配置本質上就是新增、刪除、修改過濾器。

默認情況下系統幫我們注入的這 15 個過濾器，分別對應配置不同的需求。接下來我們重點是分析下 UsernamePasswordAuthenticationFilter 這個過濾器，他是用來使用用戶名和密碼登錄認證的過濾器，但是很多情況下我們的登錄不止是簡單的用戶名和密碼，又可能是用到第三方授權登錄，這個時候我們就需要使用自定義過濾器，當然這里不做詳細說明，只是說下自定義過濾器怎么注入。

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

在開始身份認證流程之前我們需要了解下幾個基本概念

SecurityContextHolder 存儲 SecurityContext 對象。SecurityContextHolder 是一個存儲代理，有三種存儲模式分別是：

MODE_THREADLOCAL：SecurityContext 存儲在線程中。

MODE_INHERITABLETHREADLOCAL：SecurityContext 存儲在線程中，但子線程可以獲取到父線程中的 SecurityContext。

MODE_GLOBAL：SecurityContext 在所有線程中都相同。

SecurityContextHolder 默認使用 MODE_THREADLOCAL 模式，SecurityContext 存儲在當前線程中。調用 SecurityContextHolder 時不需要顯示的參數傳遞，在當前線程中可以直接獲取到 SecurityContextHolder 對象。

//獲取當前線程里面認證的對象
SecurityContext context = SecurityContextHolder.getContext();
Authentication authentication = context.getAuthentication();

//保存認證對象 (一般用于自定義認證成功保存認證對象)
SecurityContextHolder.getContext().setAuthentication(authResult);

//清空認證對象 (一般用于自定義登出清空認證對象)
SecurityContextHolder.clearContext();

Authentication 即驗證，表明當前用戶是誰。什么是驗證，比如一組用戶名和密碼就是驗證，當然錯誤的用戶名和密碼也是驗證，只不過 Spring Security 會校驗失敗。

Authentication 接口

public interface Authentication extends Principal, Serializable {
       //獲取用戶權限，一般情況下獲取到的是用戶的角色信息
       Collection getAuthorities();
       //獲取證明用戶認證的信息，通常情況下獲取到的是密碼等信息，不過登錄成功就會被移除
       Object getCredentials();
       //獲取用戶的額外信息，比如 IP 地址、經緯度等
       Object getDetails();
       //獲取用戶身份信息，在未認證的情況下獲取到的是用戶名，在已認證的情況下獲取到的是 UserDetails (暫時理解為，當前應用用戶對象的擴展)
       Object getPrincipal();
       //獲取當前 Authentication 是否已認證
       boolean isAuthenticated();
       //設置當前 Authentication 是否已認證
       void setAuthenticated(boolean isAuthenticated);
}

其實這三者很好區分，AuthenticationManager 主要就是為了完成身份認證流程，ProviderManager 是 AuthenticationManager 接口的具體實現類，ProviderManager 里面有個記錄 AuthenticationProvider 對象的集合屬性 providers，AuthenticationProvider 接口類里有兩個方法

public interface AuthenticationProvider {
    //實現具體的身份認證邏輯，認證失敗拋出對應的異常
    Authentication authenticate(Authentication authentication)
            throws AuthenticationException;
    //該認證類是否支持該 Authentication 的認證
    boolean supports(Class authentication);
}

接下來就是遍歷 ProviderManager 里面的 providers 集合，找到和合適的 AuthenticationProvider 完成身份認證。

在 UserDetailsService 接口中只有一個簡單的方法

public interface UserDetailsService {
    //根據用戶名查到對應的 UserDetails 對象
    UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;
}

對于上面概念有什么不明白的地方，在們在接下來的流程中慢慢分析

在運行到 UsernamePasswordAuthenticationFilter 過濾器的時候首先是進入其父類 AbstractAuthenticationProcessingFilter 的 doFilter() 方法中

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
        throws IOException, ServletException {
    ...
    //首先配對是不是配置的身份認證的URI,是則執行下面的認證,不是則跳過
    if (!requiresAuthentication(request, response)) {
        chain.doFilter(request, response);

        return;
    }
    ...
    Authentication authResult;

    try {
        //關鍵方法, 實現認證邏輯并返回 Authentication, 由其子類 UsernamePasswordAuthenticationFilter 實現, 由下面 5.3 詳解
        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) {
        //認證失敗調用...由下面 5.1 詳解
        unsuccessfulAuthentication(request, response, failed);

        return;
    }
    catch (AuthenticationException failed) {
        //認證失敗調用...由下面 5.1 詳解
        unsuccessfulAuthentication(request, response, failed);

        return;
    }

    // Authentication success
    if (continueChainBeforeSuccessfulAuthentication) {
        chain.doFilter(request, response);
    }
    //認證成功調用...由下面 5.2 詳解
    successfulAuthentication(request, response, chain, authResult);
}

protected void unsuccessfulAuthentication(HttpServletRequest request,
                                          HttpServletResponse response, AuthenticationException failed)
        throws IOException, ServletException {
    SecurityContextHolder.clearContext();
    ...
    rememberMeServices.loginFail(request, response);
    //該 handler 處理失敗界面跳轉和響應邏輯
    failureHandler.onAuthenticationFailure(request, response, failed);
}

這里默認配置的失敗處理 handler 是 SimpleUrlAuthenticationFailureHandler，可自定義。

public class SimpleUrlAuthenticationFailureHandler implements
        AuthenticationFailureHandler {
    ...

    public void onAuthenticationFailure(HttpServletRequest request,
            HttpServletResponse response, AuthenticationException exception)
            throws IOException, ServletException {
        //沒有配置失敗跳轉的URL則直接響應錯誤
        if (defaultFailureUrl == null) {
            logger.debug("No failure URL set, sending 401 Unauthorized error");

            response.sendError(HttpStatus.UNAUTHORIZED.value(),
                HttpStatus.UNAUTHORIZED.getReasonPhrase());
        }
        else {
            //否則
            //緩存異常
            saveException(request, exception);
            //根據配置的異常頁面是重定向還是轉發進行不同方式跳轉
            if (forwardToDestination) {
                logger.debug("Forwarding to " + defaultFailureUrl);

                request.getRequestDispatcher(defaultFailureUrl)
                        .forward(request, response);
            }
            else {
                logger.debug("Redirecting to " + defaultFailureUrl);
                redirectStrategy.sendRedirect(request, response, defaultFailureUrl);
            }
        }
    }
    //緩存異常,轉發則保存在request里面,重定向則保存在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);
            }
        }
    }
}

這里做下小拓展：用系統的錯誤處理handler，指定認證失敗跳轉的URL，在MVC里面對應的URL方法里面可以通過key從request或session里面拿到錯誤信息，反饋給前端

protected void successfulAuthentication(HttpServletRequest request,
                                        HttpServletResponse response, FilterChain chain, Authentication authResult)
        throws IOException, ServletException {
    ...
    //這里要注意很重要，將認證完成返回的 Authentication 保存到線程對應的 `SecurityContext` 中
    SecurityContextHolder.getContext().setAuthentication(authResult);

    rememberMeServices.loginSuccess(request, response, authResult);

    // Fire event
    if (this.eventPublisher != null) {
        eventPublisher.publishEvent(new InteractiveAuthenticationSuccessEvent(
                authResult, this.getClass()));
    }
    //該 handler 就是為了完成頁面跳轉
    successHandler.onAuthenticationSuccess(request, response, authResult);
}

這里默認配置的成功處理 handler 是 SavedRequestAwareAuthenticationSuccessHandler，里面的代碼就不做具體展開了，反正是跳轉到指定的認證成功之后的界面，可自定義。

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;

    ...
    //開始身份認證邏輯
    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();
        //先用前端提交過來的 username 和 password 封裝一個簡易的 AuthenticationToken
        UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(
                username, password);

        // Allow subclasses to set the "details" property
        setDetails(request, authRequest);
        //具體的認證邏輯還是交給 AuthenticationManager 對象的 authenticate(..) 方法完成,接著往下看
        return this.getAuthenticationManager().authenticate(authRequest);
    }
}

由源碼斷點跟蹤得知，最終解析是由 AuthenticationManager 接口實現類 ProviderManager 來完成

public class ProviderManager implements AuthenticationManager, MessageSourceAware,
        InitializingBean {
    ...
    private List providers = Collections.emptyList();
    ...
    
    public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
        ....
        //遍歷所有的 AuthenticationProvider, 找到合適的完成身份驗證
        for (AuthenticationProvider provider : getProviders()) {
            if (!provider.supports(toTest)) {
                continue;
            }
            ...
            try {
                //進行具體的身份驗證邏輯, 這里使用到的是 DaoAuthenticationProvider, 具體邏輯記著往下看
                result = provider.authenticate(authentication);

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

DaoAuthenticationProvider 繼承自 AbstractUserDetailsAuthenticationProvider 實現了 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 {
        ...
        // 獲得提交過來的用戶名
        String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED"
                : authentication.getName();
        //根據用戶名從緩存中查找 UserDetails
        boolean cacheWasUsed = true;
        UserDetails user = this.userCache.getUserFromCache(username);

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

            try {
                //緩存中沒有則通過 retrieveUser(..) 方法查找 (看下面 DaoAuthenticationProvider 的實現)
                user = retrieveUser(username,
                        (UsernamePasswordAuthenticationToken) authentication);
            }
            catch 
            ...
        }

        try {
            //比對前的檢查,例如賬戶以一些狀態信息(是否鎖定, 過期...)
            preAuthenticationChecks.check(user);
            //子類實現比對規則 (看下面 DaoAuthenticationProvider 的實現)
            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();
        }
        //根據最終user的一些信息重新生成具體詳細的 Authentication 對象并返回 
        return createSuccessAuthentication(principalToReturn, authentication, user);
    }
    //具體生成還是看子類實現
    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;
    }
}

接下來我們來看下 DaoAuthenticationProvider 里面的三個重要的方法，比對方式、獲取需要比對的 UserDetails 對象以及生產最終返回 Authentication 的方法。

public class DaoAuthenticationProvider extends AbstractUserDetailsAuthenticationProvider {
    ...
    //密碼比對
    @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();
        //通過 PasswordEncoder 進行密碼比對, 注: 可自定義
        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"));
        }
    }

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

    //生成身份認證通過后最終返回的 Authentication, 記錄認證的身份信息
    @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);
    }
}