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Spring Security權限管理(源碼) 雜談

最近項目需要用到Spring Security的權限控制,故花了點時間簡單的去看了一下其權限控制相關的源碼(版本為4.2)。

AccessDecisionManager

spring security是通過AccessDecisionManager進行授權管理的,先來張官方圖鎮樓。

AccessDecisionManager

AccessDecisionManager 接口定義了如下方法:

//調用AccessDecisionVoter進行投票(關鍵方法)
void decide(Authentication authentication, Object object,
        Collection<ConfigAttribute> configAttributes) throws AccessDeniedException,
        InsufficientAuthenticationException;

boolean supports(ConfigAttribute attribute);
boolean supports(Class clazz);

接下來看看它的實現類的具體實現:

AffirmativeBased

public void decide(Authentication authentication, Object object,
        Collection<ConfigAttribute> configAttributes) throws AccessDeniedException {
    int deny = 0;

    for (AccessDecisionVoter voter : getDecisionVoters()) {
        //調用AccessDecisionVoter進行vote(我們姑且稱之為投票吧),後面再看vote的源碼。
        int result = voter.vote(authentication, object, configAttributes);

        if (logger.isDebugEnabled()) {
            logger.debug("Voter: " + voter + ", returned: " + result);
        }

        switch (result) {
        case AccessDecisionVoter.ACCESS_GRANTED://值為1
            //只要有voter投票為ACCESS_GRANTED,則通過
            return;

        case AccessDecisionVoter.ACCESS_DENIED://值為-1
            deny++;

            break;

        default:
            break;
        }
    }

    if (deny > 0) {
        //如果有兩個及以上AccessDecisionVoter(姑且稱之為投票者吧)都投ACCESS_DENIED,則直接就不通過了
        throw new AccessDeniedException(messages.getMessage(
                "AbstractAccessDecisionManager.accessDenied", "Access is denied"));
    }

    // To get this far, every AccessDecisionVoter abstained
    checkAllowIfAllAbstainDecisions();
}

源碼中,有個Collection configAttributes 參數,ConfigAttribute是什麼? 這個其實是一個很靈活的東西,不同的情況代表不同的語義,比如在使用了角色控制的時候,傳入的則可能是ROLE__XXX之類的,以便ROLE_VOTER使用。具體的後面在細說。

通過以上代碼可直接看到AffirmativeBased的策略:

  • 只要有投通過(ACCESS_GRANTED)票,則直接判為通過。
  • 如果沒有投通過票且反對(ACCESS_DENIED)票在兩個及其以上的,則直接判為不通過。

UnanimousBased

public void decide(Authentication authentication, Object object,
        Collection<ConfigAttribute> attributes) throws AccessDeniedException {

    int grant = 0;
    int abstain = 0;

    List<ConfigAttribute> singleAttributeList = new ArrayList<ConfigAttribute>(1);
    singleAttributeList.add(null);

    for (ConfigAttribute attribute : attributes) {
        singleAttributeList.set(0, attribute);

        for (AccessDecisionVoter voter : getDecisionVoters()) {
            //配置的投票者進行投票
            int result = voter.vote(authentication, object, singleAttributeList);

            if (logger.isDebugEnabled()) {
                logger.debug("Voter: " + voter + ", returned: " + result);
            }

            switch (result) {
            case AccessDecisionVoter.ACCESS_GRANTED:
                grant++;

                break;

            case AccessDecisionVoter.ACCESS_DENIED:
                //只要有投票者投反對票就立馬判為無權訪問
                throw new AccessDeniedException(messages.getMessage(
                        "AbstractAccessDecisionManager.accessDenied",
                        "Access is denied"));

            default:
                abstain++;

                break;
            }
        }
    }

    // To get this far, there were no deny votes
    if (grant > 0) {
        //如果沒反對票且有通過票,那麼就判為通過
        return;
    }

    // To get this far, every AccessDecisionVoter abstained
    checkAllowIfAllAbstainDecisions();
}

由此可見UnanimousBased的策略:

  • 無論多少投票者投了多少通過(ACCESS_GRANTED)票,只要有反對票(ACCESS_DENIED),那都判為不通過。
  • 如果沒有反對票且有投票者投了通過票,那麼就判為通過。

ConsensusBased

public void decide(Authentication authentication, Object object,
        Collection<ConfigAttribute> configAttributes) throws AccessDeniedException {
    int grant = 0;
    int deny = 0;
    int abstain = 0;

    for (AccessDecisionVoter voter : getDecisionVoters()) {
        //配置的投票者進行投票
        int result = voter.vote(authentication, object, configAttributes);

        if (logger.isDebugEnabled()) {
            logger.debug("Voter: " + voter + ", returned: " + result);
        }

        switch (result) {
        case AccessDecisionVoter.ACCESS_GRANTED:
            grant++;

            break;

        case AccessDecisionVoter.ACCESS_DENIED:
            deny++;

            break;

        default:
            abstain++;

            break;
        }
    }

    if (grant > deny) {
        //通過的票數大於反對的票數則判為通過
        return;
    }

    if (deny > grant) {
        //通過的票數小於反對的票數則判為不通過
        throw new AccessDeniedException(messages.getMessage(
                "AbstractAccessDecisionManager.accessDenied", "Access is denied"));
    }

    if ((grant == deny) && (grant != 0)) {
        //this.allowIfEqualGrantedDeniedDecisions默認為true
        //通過的票數和反對的票數相等,則可根據配置allowIfEqualGrantedDeniedDecisions進行判斷是否通過
        if (this.allowIfEqualGrantedDeniedDecisions) {
            return;
        }
        else {
            throw new AccessDeniedException(messages.getMessage(
                    "AbstractAccessDecisionManager.accessDenied", "Access is denied"));
        }
    }

    // To get this far, every AccessDecisionVoter abstained
    checkAllowIfAllAbstainDecisions();
}

由此可見,ConsensusBased的策略:

  • 通過的票數大於反對的票數則判為通過。
  • 通過的票數小於反對的票數則判為不通過。
  • 通過的票數和反對的票數相等,則可根據配置allowIfEqualGrantedDeniedDecisions(默認為true)進行判斷是否通過。

到此,應該明白AffirmativeBased、UnanimousBased、ConsensusBased三者的區別了吧,spring security默認使用的是AffirmativeBased, 如果有需要,可配置為其它兩個,也可自己去實現。

##投票者
以上AccessDecisionManager的實現類都只是對權限(投票)進行管理(策略的實現),具體投票(vote)的邏輯是通過調用AccessDecisionVoter的子類(投票者)的vote方法實現的。spring security默認注冊了RoleVoter和AuthenticatedVoter兩個投票者。下面來看看其源碼。

AccessDecisionManager

boolean supports(ConfigAttribute attribute);
boolean supports(Class<?> clazz);
//核心方法,此方法由上面介紹的的AccessDecisionManager調用,子類實現此方法進行投票。
int vote(Authentication authentication, S object,
        Collection<ConfigAttribute> attributes);

RoleVoter

private String rolePrefix = "ROLE_";

//只處理ROLE_開頭的(可通過配置rolePrefix的值進行改變)
public boolean supports(ConfigAttribute attribute) {
    if ((attribute.getAttribute() != null)
            && attribute.getAttribute().startsWith(getRolePrefix())) {
        return true;
    }
    else {
        return false;
    }
}

public int vote(Authentication authentication, Object object,
        Collection<ConfigAttribute> attributes) {

    if(authentication == null) {
        //用戶沒通過認證,則投反對票
        return ACCESS_DENIED;
    }
    int result = ACCESS_ABSTAIN;
    //獲取用戶實際的權限
    Collection<? extends GrantedAuthority> authorities = extractAuthorities(authentication);

    for (ConfigAttribute attribute : attributes) {
        if (this.supports(attribute)) {
            result = ACCESS_DENIED;

            // Attempt to find a matching granted authority
            for (GrantedAuthority authority : authorities) {
                if (attribute.getAttribute().equals(authority.getAuthority())) {
                    //權限匹配則投通過票
                    return ACCESS_GRANTED;
                }
            }
        }
    }
    //如果處理過,但沒投通過票,則為反對票,如果沒處理過,那麼視為棄權(ACCESS_ABSTAIN)。
    return result;
}    

很簡單吧,同時,我們還可以通過實現AccessDecisionManager來擴展自己的voter。但是,要實現這個,我們還必須得弄清楚一個東西,那就是Collection attributes這個參數是從哪兒來的,這個是個很關鍵的參數啊。通過一張官方圖能很清晰的看出這個問題來:

接下來,就看看AccessDecisionManager的調用者AbstractSecurityInterceptor。

AbstractSecurityInterceptor

...
//上面說過默認是AffirmativeBased,可配置
private AccessDecisionManager accessDecisionManager;
...
protected InterceptorStatusToken beforeInvocation(Object object) {
    ...
    //抽象方法,子類實現,但由此也可看出ConfigAttribute是由SecurityMetadataSource(實際上,默認是DefaultFilterInvocationSecurityMetadataSource)獲取。
    Collection<ConfigAttribute> attributes = this.obtainSecurityMetadataSource()
            .getAttributes(object);
    ...
    //獲取當前認證過的用戶信息
    Authentication authenticated = authenticateIfRequired();

    try {
        //調用AccessDecisionManager
        this.accessDecisionManager.decide(authenticated, object, attributes);
    }
    catch (AccessDeniedException accessDeniedException) {
        publishEvent(new AuthorizationFailureEvent(object, attributes, authenticated,
                accessDeniedException));

        throw accessDeniedException;
    }
    ...        
}

public abstract SecurityMetadataSource obtainSecurityMetadataSource();

以上方法都是由AbstractSecurityInterceptor的子類(默認是FilterSecurityInterceptor)調用,那就再看看吧:

FilterSecurityInterceptor

...
//SecurityMetadataSource的實現類,由此可��,可通過外部配置。這也說明我們可以通過自定義SecurityMetadataSource的實現類來擴展出自己實際需要的ConfigAttribute
private FilterInvocationSecurityMetadataSource securityMetadataSource;    
...
//入口
public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {
    FilterInvocation fi = new FilterInvocation(request, response, chain);
    //關鍵方法
    invoke(fi);
}

public void invoke(FilterInvocation fi) throws IOException, ServletException {
    if ((fi.getRequest() != null)
            && (fi.getRequest().getAttribute(FILTER_APPLIED) != null)
            && observeOncePerRequest) {
        // filter already applied to this request and user wants us to observe
        // once-per-request handling, so don't re-do security checking
        fi.getChain().doFilter(fi.getRequest(), fi.getResponse());
    }
    else {
        // first time this request being called, so perform security checking
        if (fi.getRequest() != null) {
            fi.getRequest().setAttribute(FILTER_APPLIED, Boolean.TRUE);
        }
        //在這兒調用了父類(AbstractSecurityInterceptor)的方法, 也就調用了accessDecisionManager
        InterceptorStatusToken token = super.beforeInvocation(fi);

        try {
            fi.getChain().doFilter(fi.getRequest(), fi.getResponse());
        }
        finally {
            super.finallyInvocation(token);
        }
        //完了再執行(父類的方法),一前一後,AOP無處不在啊
        super.afterInvocation(token, null);
    }
}

好啦,到此應該對於Spring Security的權限管理比較清楚了。看完這個,不知你是否能擴展出一套適合自己需求的權限需求來呢,如果還不太清楚,那也沒關系,下篇就實戰一下 http://www.linuxidc.com/Linux/2016-12/138096.htm,根據它來開發一套自己的權限體系。

更多Spring Security相關教程見以下內容

Spring Security 學習筆記  http://www.linuxidc.com/Linux/2016-10/135820.htm

Spring Security3.1高級詳細開發指南 PDF http://www.linuxidc.com/Linux/2016-05/131482.htm

Spring Security 學習之數據庫認證 http://www.linuxidc.com/Linux/2014-02/97407.htm

Spring Security 學習之LDAP認證 http://www.linuxidc.com/Linux/2014-02/97406.htm

Spring Security 學習之OpenID認證 http://www.linuxidc.com/Linux/2014-02/97405.htm

Spring Security 學習之X.509認證 http://www.linuxidc.com/Linux/2014-02/97404.htm

Spring Security 學習之HTTP基本認證和HTTP摘要認證 http://www.linuxidc.com/Linux/2014-02/97403.htm

Spring Security 學習之HTTP表單驗證 http://www.linuxidc.com/Linux/2014-02/97402.htm

Spring Security異常之You must provide a configuration attribute  http://www.linuxidc.com/Linux/2015-02/113364.htm

Spring Security 的詳細介紹:請點這裡
Spring Security 的下載地址:請點這裡 

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