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对于登录功能来说，为了防止暴力破解密码，一般会对登录失败次数进行限定，在一定时间窗口超过一定次数，则锁定账户，来确保系统安全。本文主要讲述一下spring security的账户锁定。

UserDetails

spring-security-core-4.2.3.RELEASE-sources.jar!/org/springframework/security/core/userdetails/UserDetails.java

/**
 * Provides core user information.
 *
 * <p>
 * Implementations are not used directly by Spring Security for security purposes. They
 * simply store user information which is later encapsulated into {@link Authentication}
 * objects. This allows non-security related user information (such as email addresses,
 * telephone numbers etc) to be stored in a convenient location.
 * <p>
 * Concrete implementations must take particular care to ensure the non-null contract
 * detailed for each method is enforced. See
 * {@link org.springframework.security.core.userdetails.User} for a reference
 * implementation (which you might like to extend or use in your code).
 *
 * @see UserDetailsService
 * @see UserCache
 *
 * @author Ben Alex
 */
public interface UserDetails extends Serializable {
    // ~ Methods
    // ========================================================================================================

    /**
     * Returns the authorities granted to the user. Cannot return <code>null</code>.
     *
     * @return the authorities, sorted by natural key (never <code>null</code>)
     */
    Collection<? extends GrantedAuthority> getAuthorities();

    /**
     * Returns the password used to authenticate the user.
     *
     * @return the password
     */
    String getPassword();

    /**
     * Returns the username used to authenticate the user. Cannot return <code>null</code>
     * .
     *
     * @return the username (never <code>null</code>)
     */
    String getUsername();

    /**
     * Indicates whether the user's account has expired. An expired account cannot be
     * authenticated.
     *
     * @return <code>true</code> if the user's account is valid (ie non-expired),
     * <code>false</code> if no longer valid (ie expired)
     */
    boolean isAccountNonExpired();

    /**
     * Indicates whether the user is locked or unlocked. A locked user cannot be
     * authenticated.
     *
     * @return <code>true</code> if the user is not locked, <code>false</code> otherwise
     */
    boolean isAccountNonLocked();

    /**
     * Indicates whether the user's credentials (password) has expired. Expired
     * credentials prevent authentication.
     *
     * @return <code>true</code> if the user's credentials are valid (ie non-expired),
     * <code>false</code> if no longer valid (ie expired)
     */
    boolean isCredentialsNonExpired();

    /**
     * Indicates whether the user is enabled or disabled. A disabled user cannot be
     * authenticated.
     *
     * @return <code>true</code> if the user is enabled, <code>false</code> otherwise
     */
    boolean isEnabled();
}

spring security的UserDetails内置了isAccountNonLocked方法来判断账户是否被锁定

AbstractUserDetailsAuthenticationProvider#authenticate

spring-security-core-4.2.3.RELEASE-sources.jar!/org/springframework/security/authentication/dao/AbstractUserDetailsAuthenticationProvider.java

public abstract class AbstractUserDetailsAuthenticationProvider implements
        AuthenticationProvider, InitializingBean, MessageSourceAware {
    protected MessageSourceAccessor messages = SpringSecurityMessageSource.getAccessor();
    private UserCache userCache = new NullUserCache();
    private boolean forcePrincipalAsString = false;
    protected boolean hideUserNotFoundExceptions = true;
    private UserDetailsChecker preAuthenticationChecks = new DefaultPreAuthenticationChecks();
    private UserDetailsChecker postAuthenticationChecks = new DefaultPostAuthenticationChecks();
    private GrantedAuthoritiesMapper authoritiesMapper = new NullAuthoritiesMapper();

    public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
        Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication,
                messages.getMessage(
                        "AbstractUserDetailsAuthenticationProvider.onlySupports",
                        "Only UsernamePasswordAuthenticationToken is supported"));

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

        boolean cacheWasUsed = true;
        UserDetails user = this.userCache.getUserFromCache(username);

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

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

                if (hideUserNotFoundExceptions) {
                    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 {
            preAuthenticationChecks.check(user);
            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();
        }

        return createSuccessAuthentication(principalToReturn, authentication, user);
    }
    //......
}

AbstractUserDetailsAuthenticationProvider的authenticate里头内置了preAuthenticationChecks和postAuthenticationChecks，而preAuthenticationChecks使用的是DefaultPreAuthenticationChecks

默认的DaoAuthenticationProvider继承自AbstractUserDetailsAuthenticationProvider

AbstractUserDetailsAuthenticationProvider#DefaultPreAuthenticationChecks

private class DefaultPreAuthenticationChecks implements UserDetailsChecker {
        public void check(UserDetails user) {
            if (!user.isAccountNonLocked()) {
                logger.debug("User account is locked");

                throw new LockedException(messages.getMessage(
                        "AbstractUserDetailsAuthenticationProvider.locked",
                        "User account is locked"));
            }

            if (!user.isEnabled()) {
                logger.debug("User account is disabled");

                throw new DisabledException(messages.getMessage(
                        "AbstractUserDetailsAuthenticationProvider.disabled",
                        "User is disabled"));
            }

            if (!user.isAccountNonExpired()) {
                logger.debug("User account is expired");

                throw new AccountExpiredException(messages.getMessage(
                        "AbstractUserDetailsAuthenticationProvider.expired",
                        "User account has expired"));
            }
        }
    }

这里会对账户的isAccountNonLocked进行判断，如果被锁定，则在登录的时候，抛出LockedException

实现账户锁定

实现大致思路就是基于用户登录失败次数进行时间窗口统计，超过阈值则将用户的isAccountNonLocked设置为true，那么在下次登录时，则会抛出LockedException。

这里基于AuthenticationFailureBadCredentialsEvent事件来实现
时间窗口统计使用ratelimitj-inmemory组件

        <dependency>
            <groupId>es.moki.ratelimitj</groupId>
            <artifactId>ratelimitj-inmemory</artifactId>
            <version>0.4.1</version>
        </dependency>

分布式场景可以替换为基于redis实现

AuthenticationFailureBadCredentialsEvent

在登录失败的时候，spring security会抛出AuthenticationFailureBadCredentialsEvent事件，基于事件监听机制，可以实现

@Component
public class LoginFailureListener implements ApplicationListener<AuthenticationFailureBadCredentialsEvent> {

    private static final Logger LOGGER = LoggerFactory.getLogger(LoginFailureListener.class);

    //错误了第四次返回true,然后锁定账号,第五次即使密码正确也会报账户锁定
    Set<RequestLimitRule> rules = Collections.singleton(RequestLimitRule.of(10, TimeUnit.MINUTES,3)); // 3 request per 10 minute, per key
    RequestRateLimiter limiter = new InMemorySlidingWindowRequestRateLimiter(rules);

    @Autowired
    UserDetailsManager userDetailsManager;

    @Override
    public void onApplicationEvent(AuthenticationFailureBadCredentialsEvent event) {
        if (event.getException().getClass().equals(UsernameNotFoundException.class)) {
            return;
        }

        String userId = event.getAuthentication().getName();

        boolean reachLimit = limiter.overLimitWhenIncremented(userId);

        if(reachLimit){
            User user = (User) userDetailsManager.loadUserByUsername(userId);

            LOGGER.info("user:{} is locked",user);

            User updated = new User(user.getUsername(),user.getPassword(),user.isEnabled(),user.isAccountNonExpired(),user.isAccountNonExpired(),false,user.getAuthorities());

            userDetailsManager.updateUser(updated);
        }
    }
}

这里排除了用户名错误的情况。然后每失败一次，就进行时间窗口统计，如果超出阈值，则立马更新用户的accountNonLocked属性。那么第四次输错密码时，user的accountNonLocked属性被更新为false，之后第五次无论密码对错，则会抛出LockedException

上面的方案，还需要在时间窗口之后重置这个accountNonLocked属性，这里没有实现。

小结

spring security还是蛮强大的，在AbstractUserDetailsAuthenticationProvider的authenticate里头内置了preAuthenticationChecks，帮你建立关于登录前的各种预校验。具体的实现就交给应用层。