spring security 的callstack分析

5月 17, 2017 | Nix.Huang

在web.xml中有如下的filter声明
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<filter>
<filter-name>springSecurityFilterChain</filter-name>
<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>

<filter-mapping>
<filter-name>springSecurityFilterChain</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

<filter-name>springSecurityFilterChain</filter-name>

<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>

</filter>

<filter-mapping>

<filter-name>springSecurityFilterChain</filter-name>

<url-pattern>/*</url-pattern>

</filter-mapping>

在这里，DelegatingFilterProxy的filter-name是有严格要求的，不能乱定义，默认的为springSecurityFilterChain，其实就是在spring context中FilterChainProxy bean的别名。
在spring context中有如下定义

<global-method-security pre-post-annotations="enabled" />
 <http pattern="/static/**" security="none"/>
 <http pattern="/loggedout.jsp" security="none"/>
 <http >
 <intercept-url pattern="/secure/extreme/**" access="hasAuthority('supervisor')"/>
 <intercept-url pattern="/secure/**" access="authenticated" />
 <intercept-url pattern="/**" access="permitAll" />
 <form-login />
 <logout logout-success-url="/loggedout.jsp" delete-cookies="JSESSIONID"/>
 <csrf disabled="true"/>
 <anonymous enabled="false"/>
 <session-management invalid-session-url="/timeout.jsp">
 <concurrency-control max-sessions="1" error-if-maximum-exceeded="true" />
 </session-management>
 </http>
 
 <authentication-manager> <!--对应ProviderManager实例-->
 <authentication-provider> <!--对应DaoAuthenticationProvider实例-->
 <user-service><!--对应InMemoryUserDetailsManager实例-->
 <user name="rod" password="koala" authorities="supervisor" />
 <user name="dianne" password="emu" authorities="ROLE_user,ROLE_teller" />
 <user name="scott" password="wombat" authorities="ROLE_user" />
 <user name="peter" password="opal" authorities="ROLE_user" />
 </user-service>
 </authentication-provider>
 </authentication-manager>

<global-method-security pre-post-annotations="enabled" />

<http >

<intercept-url pattern="/secure/extreme/**" access="hasAuthority('supervisor')"/>

<intercept-url pattern="/secure/**" access="authenticated" />

<intercept-url pattern="/**" access="permitAll" />

<form-login />

<session-management invalid-session-url="/timeout.jsp">

<concurrency-control max-sessions="1" error-if-maximum-exceeded="true" />

</session-management>

</http>

<authentication-manager>

<authentication-provider>

<user-service>

</user-service>

</authentication-provider>

</authentication-manager>

前面提到的FilterChainProxy是对所有<http>元素封装，当请求到来时，比较请求的路径是否匹配<http>的pattern。如果匹配，就执行该<http>定义的filter链。具体的实现参考FilterChainProxy.doFilterInternal方法。
核心filter UsernamePasswordAuthenticationFilter的作用是完成用户的认证，用spring security的官方说法应该是"authenticate Credential"。主要的逻辑是调用ProviderManager.authenticate方法，在该方法中调用合适的AuthenticationProvider来完成真正的鉴权，本例为<authentication-provider>对应的DaoAuthenticationProvider。
核心filter FilterSecurityInterceptor的作用是判断当前用户是否拥有被请求资源的访问权限，在FilterSecurityInterceptor的父类 AbstractSecurityInterceptor.beforeInvocation方法中，先获取请求资源匹配的<intercept-url>元素对应的access定义，用Collection<ConfigAttribute>表示，然后调用AccessDecisionManager.decide进行是否有访问权限的决策，基于namespace配置时AccessDecisionManager的默认实现为AffirmativeBased。具体的逻辑参考AffirmativeBased.decide方法

调用栈如下：

spring-security-classic-callstack