浅析SpringSecurity的AuthenticationEntryPoint认证入口点及其实现类简介及AccessDeineHandler

一、AuthenticationEntryPoint简介

　　AuthenticationEntryPoint是Spring Security Web一个概念模型接口，顾名思义，他所建模的概念是：“认证入口点”。

　　它在用户请求处理过程中遇到认证异常时，被ExceptionTranslationFilter用于开启特定认证方案(authentication schema)的认证流程。

　　该接口只定义了一个方法：

void commence(HttpServletRequest request, HttpServletResponse response,
            AuthenticationException authException) throws IOException, ServletException;

　　这里参数request是遇到了认证异常authException用户请求，response是将要返回给客户的相应，方法commence实现，也就是相应的认证方案逻辑会修改response并返回给用户引导用户进入认证流程。

　　在该方法被调用前，ExceptionTranslationFilter会做好如下工作：填充属性HttpSession，使用属性名称为AbstractAuthenticationProcessingFilter.SPRING_SECURITY_SAVED_REQUEST_KEY

二、`AuthenticationEntryPoint`源代码

package org.springframework.security.web;

import org.springframework.security.core.AuthenticationException;
import org.springframework.security.web.access.ExceptionTranslationFilter;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public interface AuthenticationEntryPoint {

    /**
     * Commences an authentication scheme.
     * 
     * ExceptionTranslationFilter will populate the HttpSession
     * attribute named
     * AbstractAuthenticationProcessingFilter.SPRING_SECURITY_SAVED_REQUEST_KEY
     * with the requested target URL before calling this method.
     * 
     * Implementations should modify the headers on the ServletResponse as
     * necessary to commence the authentication process.
     *
     * @param request that resulted in an AuthenticationException
     * @param response so that the user agent can begin authentication
     * @param authException that caused the invocation
     *
     */
    void commence(HttpServletRequest request, HttpServletResponse response,
            AuthenticationException authException) throws IOException, ServletException;
}

　　Spring Security Web 为AuthenticationEntryPoint提供了一些内置实现：

1、Http403ForbiddenEntryPoint：设置响应状态字为403，并非触发一个真正的认证流程。通常在一个预验证(pre-authenticated authentication)已经得出结论需要拒绝用户请求的情况被用于拒绝用户请求。

2、HttpStatusEntryPoint：设置特定的响应状态字，并非触发一个真正的认证流程。

3、LoginUrlAuthenticationEntryPoint：根据配置计算出登录页面url，将用户重定向到该登录页面从而开始一个认证流程。

4、BasicAuthenticationEntryPoint：对应标准Http Basic认证流程的触发动作，向响应写入状态字401和头部WWW-Authenticate:"Basic realm="xxx"触发标准Http Basic认证流程。

5、DigestAuthenticationEntryPoint：对应标准Http Digest认证流程的触发动作，向响应写入状态字401和头部WWW-Authenticate:"Digest realm="xxx"触发标准Http Digest认证流程。

6、DelegatingAuthenticationEntryPoint：这是一个代理，将认证任务委托给所代理的多个AuthenticationEntryPoint对象，其中一个被标记为缺省AuthenticationEntryPoint。

三、自定义认证返回

public class ExamAuthenticationEntryPoint implements AuthenticationEntryPoint {
    @Override
    public void commence(HttpServletRequest request, HttpServletResponse response, AuthenticationException e) throws IOException {
        response.setStatus(HttpStatus.UNAUTHORIZED.value());
        OperationInfo info = OperationInfo.failure("请登录后操作");
        HttpResponseUtil.setResponseMessage(response, info);
    }
}

1、实现 AuthenticationEntryPoint 类，覆写 commence 方法。

2、设置ExamAuthenticationEntryPoint

@Override
protected void configure(HttpSecurity http) throws Exception {
    http.csrf()......
    .exceptionHandling().authenticationEntryPoint(new ExamAuthenticationEntryPoint())
    ......
}

四、自定义AccessDeineHandler

　　AuthenticationEntryPoint 用来解决匿名用户访问无权限资源时的异常 —— 也就是未授权的问题

　　AccessDeineHandler 用来解决认证过的用户访问无权限资源时的异常 —— 也就是权限不足的问题

public class CustomAccessDeineHandler implements AccessDeniedHandler {
    @Override
    public void handle(HttpServletRequest request, HttpServletResponse response,
            AccessDeniedException accessDeniedException) throws IOException, ServletException {
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/javascript;charset=utf-8");
        response.getWriter().print(JSONObject.toJSONString(RestMsg.error("没有访问权限!")));
    }
}

//添加自定义异常入口，处理accessdeine异常
http.exceptionHandling().authenticationEntryPoint(new CustomAuthenticationEntryPoint())
.accessDeniedHandler(new CustomAccessDeineHandler());

// 禁用缓存
http.headers().cacheControl();
// 添加JWT filter
http.addFilterBefore(authenticationTokenFilterBean(), UsernamePasswordAuthenticationFilter.class);
//添加未授权处理
http.exceptionHandling().authenticationEntryPoint(new CustomAuthenticationEntryPoint());
//权限不足处理
http.exceptionHandling().accessDeniedHandler(getAccessDeniedHandler());