Shiro源码解析-登录篇

本文以循序渐进的方式解析Shiro整个login过程的处理，读者可以边阅读本文边自己看代码来思考体会，如有问题，欢迎评论区探讨！

笔者shiro的demo源码路径：https://github.com/roostinghawk/ShiroDemo.git

1. 入口：Suject.login （比如Spring一般为LoginController）

    @PostMapping("/login")
    public String login(@RequestParam("loginName") String loginName, @RequestParam("password") String password, Model model){
        UsernamePasswordToken usernamePasswordToken = new UsernamePasswordToken(loginName, password);
        Subject subject = SecurityUtils.getSubject();

        try {
            subject.login(usernamePasswordToken); // 入口
        }catch (IncorrectCredentialsException ice){
            model.addAttribute("login","password error");
            return "error";
        }catch (UnknownAccountException uae) {
            model.addAttribute("login","userName error");
            return "error";
        }return "redirect:/index";
    }

2. 接口Subject实现类DelegatingSubject的login方法

    public void login(AuthenticationToken token) throws AuthenticationException {
        clearRunAsIdentitiesInternal();
        Subject subject = securityManager.login(this, token); // 此处调用SecurityManager登录，从此入口向下解析

        PrincipalCollection principals;

        String host = null;

        if (subject instanceof DelegatingSubject) {
            DelegatingSubject delegating = (DelegatingSubject) subject;
            //we have to do this in case there are assumed identities - we don't want to lose the 'real' principals:
            principals = delegating.principals;
            host = delegating.host;
        } else {
            principals = subject.getPrincipals();
        }

        if (principals == null || principals.isEmpty()) {
            String msg = "Principals returned from securityManager.login( token ) returned a null or " +
                    "empty value.  This value must be non null and populated with one or more elements.";
            throw new IllegalStateException(msg);
        }
        this.principals = principals;
        this.authenticated = true;
        if (token instanceof HostAuthenticationToken) {
            host = ((HostAuthenticationToken) token).getHost();
        }
        if (host != null) {
            this.host = host;
        }
        Session session = subject.getSession(false);
        if (session != null) {
            this.session = decorate(session);
        } else {
            this.session = null;
        }
    }

3. 接口SecurityManager实现类DefaultSecurityManager的login方法

    /**
     * First authenticates the {@code AuthenticationToken} argument, and if successful, constructs a
     * {@code Subject} instance representing the authenticated account's identity.
     * <p/>
     * Once constructed, the {@code Subject} instance is then {@link #bind bound} to the application for
     * subsequent access before being returned to the caller.
     *
     * @param token the authenticationToken to process for the login attempt.
     * @return a Subject representing the authenticated user.
     * @throws AuthenticationException if there is a problem authenticating the specified {@code token}.
     */
    public Subject login(Subject subject, AuthenticationToken token) throws AuthenticationException {
        AuthenticationInfo info;
        try {
            info = authenticate(token); // 验证凭证：authenticate(token)
        } catch (AuthenticationException ae) {
            try {
                onFailedLogin(token, ae, subject);
            } catch (Exception e) {
                if (log.isInfoEnabled()) {
                    log.info("onFailedLogin method threw an " +
                            "exception.  Logging and propagating original AuthenticationException.", e);
                }
            }
            throw ae; //propagate
        }

        Subject loggedIn = createSubject(token, info, subject); // 创建Subject：createSubject（涉及到Session的创建，不在此文解析）

        onSuccessfulLogin(token, info, loggedIn); // rememberMe处理

        return loggedIn;
    }

对于1）的代码，继续向下分析，是使用Authenticator的委托来实现

    /**
     * Delegates to the wrapped {@link org.apache.shiro.authc.Authenticator Authenticator} for authentication.
     */
    public AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {
        return this.authenticator.authenticate(token);
    }

实际调用的是抽象类AbstractAuthenticator的authenticate的方法

    public final AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {

        if (token == null) {
            throw new IllegalArgumentException("Method argument (authentication token) cannot be null.");
        }

        log.trace("Authentication attempt received for token [{}]", token);

        AuthenticationInfo info;
        try {
            info = doAuthenticate(token);
            if (info == null) {
                String msg = "No account information found for authentication token [" + token + "] by this " +
                        "Authenticator instance.  Please check that it is configured correctly.";
                throw new AuthenticationException(msg);
            }
        } catch (Throwable t) {
            AuthenticationException ae = null;
            if (t instanceof AuthenticationException) {
                ae = (AuthenticationException) t;
            }
            if (ae == null) {
                //Exception thrown was not an expected AuthenticationException.  Therefore it is probably a little more
                //severe or unexpected.  So, wrap in an AuthenticationException, log to warn, and propagate:
                String msg = "Authentication failed for token submission [" + token + "].  Possible unexpected " +
                        "error? (Typical or expected login exceptions should extend from AuthenticationException).";
                ae = new AuthenticationException(msg, t);
                if (log.isWarnEnabled())
                    log.warn(msg, t);
            }
            try {
                notifyFailure(token, ae);
            } catch (Throwable t2) {
                if (log.isWarnEnabled()) {
                    String msg = "Unable to send notification for failed authentication attempt - listener error?.  " +
                            "Please check your AuthenticationListener implementation(s).  Logging sending exception " +
                            "and propagating original AuthenticationException instead...";
                    log.warn(msg, t2);
                }
            }

            throw ae;
        }

        log.debug("Authentication successful for token [{}].  Returned account [{}]", token, info);

        notifySuccess(token, info);

        return info;
    }

查看方法doAuthenticate的实现，实际在子类ModularRealmAuthenticator

    protected AuthenticationInfo doAuthenticate(AuthenticationToken authenticationToken) throws AuthenticationException {
        assertRealmsConfigured();
        Collection<Realm> realms = getRealms(); // 看到这里，大家应该明白realm的查找和执行时机了吧（在config中设置SecurityManager的realm）

        if (realms.size() == 1) {
            return doSingleRealmAuthentication(realms.iterator().next(), authenticationToken);
        } else {
            return doMultiRealmAuthentication(realms, authenticationToken);
        }
    }

在demo中，我们使用的单一realm，所以接下来

    protected AuthenticationInfo doSingleRealmAuthentication(Realm realm, AuthenticationToken token) {
        if (!realm.supports(token)) {
            String msg = "Realm [" + realm + "] does not support authentication token [" +
                    token + "].  Please ensure that the appropriate Realm implementation is " +
                    "configured correctly or that the realm accepts AuthenticationTokens of this type.";
            throw new UnsupportedTokenException(msg);
        }
        AuthenticationInfo info = realm.getAuthenticationInfo(token);  // 此处调用的还不是自定义的realm的方法，而是其父类AuthenticatingRealm
        if (info == null) {
            String msg = "Realm [" + realm + "] was unable to find account data for the " +
                    "submitted AuthenticationToken [" + token + "].";
            throw new UnknownAccountException(msg);
        }
        return info;
    }

AuthenticatingRealm的getAuthenticationInfo

    public final AuthenticationInfo getAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {

        AuthenticationInfo info = getCachedAuthenticationInfo(token); // 先从缓存取验证信息
        if (info == null) {
            //otherwise not cached, perform the lookup:
            info = doGetAuthenticationInfo(token); // 此时才会真正的执行自定义的realm
            log.debug("Looked up AuthenticationInfo [{}] from doGetAuthenticationInfo", info);
            if (token != null && info != null) {
                cacheAuthenticationInfoIfPossible(token, info);
            }
        } else {
            log.debug("Using cached authentication info [{}] to perform credentials matching.", info);
        }

        if (info != null) {
            assertCredentialsMatch(token, info); // 真正的密码校验是在realm执行完成之后的
        } else {
            log.debug("No AuthenticationInfo found for submitted AuthenticationToken [{}].  Returning null.", token);
        }

        return info;
    }

大家这时候可能有一个疑问，为什么父类的protected方法会跑到子类执行呢？

这是因为执行的realm实例本身就是自定义的MyRealm，对于子类未实现而在抽象父类中实现的方法，当然是执行父类的方法，而对于已经覆盖的方法，当然也会走到子类的实现，这就是抽象和继承的好处！

接下来看自定义的realm

    /**
     * 提供帐户信息，返回认证信息 （其实realm并不负责校验密码，而是负责把用户信息从数据源中取出来）
     * @param authenticationToken
     * @return
     * @throws AuthenticationException
     */
    @Override
    protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken authenticationToken) throws AuthenticationException {
        String loginName = (String)authenticationToken.getPrincipal();
        User user = userService.findUserByLoginName(loginName);
        if(user == null) {
            //用户不存在就抛出异常
            throw new UnknownAccountException();
        }

        //密码可以通过SimpleHash加密，然后保存进数据库。
        //此处是获取数据库内的账号、密码、盐值，保存到登陆信息info中
        return new SimpleAuthenticationInfo(
                loginName,
                user.getPassword(),
                ByteSource.Util.bytes(Hex.decode(user.getSalt())),
                getName());
    }

4. 自定义realm执行完后，会返回到AuthenticatingRealm的getAuthenticationInfo进行密码校验assertCredentialsMatch （当然前提是取到了该用户）

5. 一步步回溯到DefaultSecurityManager的login方法中进行登录成功后的处理：session保存和rememberMe处理

（在config中设置SecurityManager的realm属性设置）