源码分析shiro认证授权流程

1. shiro介绍

Apache Shiro是一个强大易用的Java安全框架，提供了认证、授权、加密和会话管理等功能： 

• 认证 - 用户身份识别，常被称为用户“登录”；
• 授权 - 访问控制；
• 密码加密 - 保护或隐藏数据防止被偷窥；
• 会话管理 - 每用户相关的时间敏感的状态。

对于任何一个应用程序，Shiro都可以提供全面的安全管理服务。并且相对于其他安全框架，Shiro要简单的多。

2. shiro源码概况

    先要了解shiro的基本框架(见http://www.cnblogs.com/davidwang456/p/4425145.html)。

    然后看一下各个组件之间的关系：

一下内容参考：http://kdboy.iteye.com/blog/1154644

Subject：即“当前操作用户”。但是，在Shiro中，Subject这一概念并不仅仅指人，也可以是第三方进程、后台帐户（Daemon Account）或其他类似事物。它仅仅意味着“当前跟软件交互的东西”。但考虑到大多数目的和用途，你可以把它认为是Shiro的“用户”概念。 
Subject代表了当前用户的安全操作，SecurityManager则管理所有用户的安全操作。 

SecurityManager：它是Shiro框架的核心，典型的Facade模式，Shiro通过SecurityManager来管理内部组件实例，并通过它来提供安全管理的各种服务。 

Realm： Realm充当了Shiro与应用安全数据间的“桥梁”或者“连接器”。也就是说，当对用户执行认证（登录）和授权（访问控制）验证时，Shiro会从应用配置的Realm中查找用户及其权限信息。 
从这个意义上讲，Realm实质上是一个安全相关的DAO：它封装了数据源的连接细节，并在需要时将相关数据提供给Shiro。当配置Shiro时，你必须至少指定一个Realm，用于认证和（或）授权。配置多个Realm是可以的，但是至少需要一个。 
Shiro内置了可以连接大量安全数据源（又名目录）的Realm，如LDAP、关系数据库（JDBC）、类似INI的文本配置资源以及属性文件等。如果缺省的Realm不能满足需求，你还可以插入代表自定义数据源的自己的Realm实现。

Shiro主要组件还包括： 
Authenticator ：认证就是核实用户身份的过程。这个过程的常见例子是大家都熟悉的“用户/密码”组合。多数用户在登录软件系统时，通常提供自己的用户名（当事人）和支持他们的密码（证书）。如果存储在系统中的密码（或密码表示）与用户提供的匹配，他们就被认为通过认证。 
Authorizer ：授权实质上就是访问控制 - 控制用户能够访问应用中的哪些内容，比如资源、Web页面等等。 
SessionManager ：在安全框架领域，Apache Shiro提供了一些独特的东西：可在任何应用或架构层一致地使用Session API。即，Shiro为任何应用提供了一个会话编程范式 - 从小型后台独立应用到大型集群Web应用。这意味着，那些希望使用会话的应用开发者，不必被迫使用Servlet或EJB容器了。或者，如果正在使用这些容器，开发者现在也可以选择使用在任何层统一一致的会话API，取代Servlet或EJB机制。 
CacheManager :对Shiro的其他组件提供缓存支持。 

3. 做一个demo，跑shiro的源码，从login开始：

第一步：用户根据表单信息填写用户名和密码，然后调用登陆按钮。内部执行如下：

    UsernamePasswordToken token = new UsernamePasswordToken(loginForm.getUsername(), loginForm.getPassphrase());

    token.setRememberMe(true);

    Subject currentUser = SecurityUtils.getSubject();

    currentUser.login(token);

第二步：代理DelegatingSubject继承Subject执行login

 public void login(AuthenticationToken token) throws AuthenticationException {
        clearRunAsIdentitiesInternal();
        Subject subject = securityManager.login(this, token);

        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;
        }
    }

第三步：调用DefaultSecurityManager继承SessionsSecurityManager执行login方法

    public Subject login(Subject subject, AuthenticationToken token) throws AuthenticationException {
        AuthenticationInfo info;
        try {
            info = 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);

        onSuccessfulLogin(token, info, loggedIn);

        return loggedIn;
    }

第四步：认证管理器AuthenticatingSecurityManager继承RealmSecurityManager执行authenticate方法：

    /**
     * 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);
    }

第五步：抽象认证管理器AbstractAuthenticator继承Authenticator, LogoutAware 执行authenticate方法：

public final AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {

        if (token == null) {
            throw new IllegalArgumentException("Method argumet (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);
            }
            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;
    }

第六步：ModularRealmAuthenticator继承AbstractAuthenticator执行doAuthenticate方法

    protected AuthenticationInfo doAuthenticate(AuthenticationToken authenticationToken) throws AuthenticationException {
        assertRealmsConfigured();
        Collection<Realm> realms = getRealms();
        if (realms.size() == 1) {
            return doSingleRealmAuthentication(realms.iterator().next(), authenticationToken);
        } else {
            return doMultiRealmAuthentication(realms, authenticationToken);
        }
    }

接着调用：

    /**
     * Performs the authentication attempt by interacting with the single configured realm, which is significantly
     * simpler than performing multi-realm logic.
     *
     * @param realm the realm to consult for AuthenticationInfo.
     * @param token the submitted AuthenticationToken representing the subject's (user's) log-in principals and credentials.
     * @return the AuthenticationInfo associated with the user account corresponding to the specified {@code token}
     */
    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);
        if (info == null) {
            String msg = "Realm [" + realm + "] was unable to find account data for the " +
                    "submitted AuthenticationToken [" + token + "].";
            throw new UnknownAccountException(msg);
        }
        return info;
    }

第七步：AuthenticatingRealm继承CachingRealm执行getAuthenticationInfo方法

   public final AuthenticationInfo getAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {

        AuthenticationInfo info = getCachedAuthenticationInfo(token); //从缓存中读取
        if (info == null) {
            //otherwise not cached, perform the lookup:
            info = doGetAuthenticationInfo(token);  //缓存中读不到，则到数据库或者ldap或者jndi等去读
            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);
        } else {
            log.debug("No AuthenticationInfo found for submitted AuthenticationToken [{}].  Returning null.", token);
        }

        return info;
    }

1. 从缓存中读取的方法：

    /**
     * Checks to see if the authenticationCache class attribute is null, and if so, attempts to acquire one from
     * any configured {@link #getCacheManager() cacheManager}.  If one is acquired, it is set as the class attribute.
     * The class attribute is then returned.
     *
     * @return an available cache instance to be used for authentication caching or {@code null} if one is not available.
     * @since 1.2
     */
    private Cache<Object, AuthenticationInfo> getAuthenticationCacheLazy() {

        if (this.authenticationCache == null) {

            log.trace("No authenticationCache instance set.  Checking for a cacheManager...");

            CacheManager cacheManager = getCacheManager();

            if (cacheManager != null) {
                String cacheName = getAuthenticationCacheName();
                log.debug("CacheManager [{}] configured.  Building authentication cache '{}'", cacheManager, cacheName);
                this.authenticationCache = cacheManager.getCache(cacheName);
            }
        }

        return this.authenticationCache;
    }

2. 从数据库中读取的方法：

JdbcRealm继承 AuthorizingRealm执行doGetAuthenticationInfo方法

 protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {

        UsernamePasswordToken upToken = (UsernamePasswordToken) token;
        String username = upToken.getUsername();

        // Null username is invalid
        if (username == null) {
            throw new AccountException("Null usernames are not allowed by this realm.");
        }

        Connection conn = null;
        SimpleAuthenticationInfo info = null;
        try {
            conn = dataSource.getConnection();

            String password = null;
            String salt = null;
            switch (saltStyle) {
            case NO_SALT:
                password = getPasswordForUser(conn, username)[0];
                break;
            case CRYPT:
                // TODO: separate password and hash from getPasswordForUser[0]
                throw new ConfigurationException("Not implemented yet");
                //break;
            case COLUMN:
                String[] queryResults = getPasswordForUser(conn, username);
                password = queryResults[0];
                salt = queryResults[1];
                break;
            case EXTERNAL:
                password = getPasswordForUser(conn, username)[0];
                salt = getSaltForUser(username);
            }

            if (password == null) {
                throw new UnknownAccountException("No account found for user [" + username + "]");
            }

            info = new SimpleAuthenticationInfo(username, password.toCharArray(), getName());
            
            if (salt != null) {
                info.setCredentialsSalt(ByteSource.Util.bytes(salt));
            }

        } catch (SQLException e) {
            final String message = "There was a SQL error while authenticating user [" + username + "]";
            if (log.isErrorEnabled()) {
                log.error(message, e);
            }

            // Rethrow any SQL errors as an authentication exception
            throw new AuthenticationException(message, e);
        } finally {
            JdbcUtils.closeConnection(conn);
        }

        return info;
    }

接着调用sql语句：

 private String[] getPasswordForUser(Connection conn, String username) throws SQLException {

        String[] result;
        boolean returningSeparatedSalt = false;
        switch (saltStyle) {
        case NO_SALT:
        case CRYPT:
        case EXTERNAL:
            result = new String[1];
            break;
        default:
            result = new String[2];
            returningSeparatedSalt = true;
        }
        
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            ps = conn.prepareStatement(authenticationQuery);
            ps.setString(1, username);

            // Execute query
            rs = ps.executeQuery();

            // Loop over results - although we are only expecting one result, since usernames should be unique
            boolean foundResult = false;
            while (rs.next()) {

                // Check to ensure only one row is processed
                if (foundResult) {
                    throw new AuthenticationException("More than one user row found for user [" + username + "]. Usernames must be unique.");
                }

                result[0] = rs.getString(1);
                if (returningSeparatedSalt) {
                    result[1] = rs.getString(2);
                }

                foundResult = true;
            }
        } finally {
            JdbcUtils.closeResultSet(rs);
            JdbcUtils.closeStatement(ps);
        }

        return result;
    }

其中authenticationQuery定义如下：

 protected String authenticationQuery = DEFAULT_AUTHENTICATION_QUERY;
 protected static final String DEFAULT_AUTHENTICATION_QUERY = "select password from users where username = ?";

4. 小结

Apache Shiro 是功能强大并且容易集成的开源权限框架，它能够完成认证、授权、加密、会话管理等功能。认证和授权为权限控制的核心，简单来说，“认证”就是证明你是谁？ Web 应用程序一般做法通过表单提交用户名及密码达到认证目的。“授权”即是否允许已认证用户访问受保护资源。

参考文献：

http://kdboy.iteye.com/blog/1154644

http://www.ibm.com/developerworks/cn/java/j-lo-shiro/