Spring Security框架下Restful Token的验证方案

项目使用Restful的规范，权限内容的访问，考虑使用Token验证的权限解决方案。

验证方案（简要概括）：

首先，用户需要登陆，成功登陆后返回一个Token串；

然后用户访问有权限的内容时需要上传Token串进行权限验证

代码方案：

Spring MVC + Spring Security + Redis的框架下实现权限验证，此文重点谈谈Spring Security下的Token验证实现。

首先，看看spring security的配置：

<http pattern="/service/secure/**"
          entry-point-ref="serviceUnauthorizedEntryPoint"
          create-session="stateless">
          <!-- Added after moving to Spring Boot 1.3 + Spring Security 4.x, otherwise we could not login with basic auth because of: Expected CSRF token not found TODO: Please, mind, that I did not migrate this XML to Spring Security 4.x except for this element -->
          <csrf disabled="true"/>
          
          <intercept-url pattern="/service/secure/admin/login*" access="permitAll"/>
          
          <custom-filter ref="preTokenAuthenticationFilter" before="PRE_AUTH_FILTER" />
    </http>

接下来详细说明配置以及访问流程：

1. 考虑到支持Restful规范，所以spring security需要设置create-session为stateless状态

2. 当访问权限验证失败是，根据Restful规范返回401 Unauthorized，因此需要设定entry-point-ref，重新指向一个自定义的entrypoint如下：

public class ServiceUnauthorizedEntryPoint implements AuthenticationEntryPoint {

    private static final Logger logger = LoggerFactory.getLogger(ServiceTokenAuthenticationFilter.class);
    
    @Override
    public void commence(HttpServletRequest request, HttpServletResponse response,
            AuthenticationException arg2) throws IOException, ServletException {
        // return 401 UNAUTHORIZED status code if the user is not authenticated
        logger.debug(" *** UnauthorizedEntryPoint.commence: " + request.getRequestURI());
        response.sendError(HttpServletResponse.SC_UNAUTHORIZED);
    }

}

3. Token的验证重点在于PRE_AUTH_FILTER的拦截器

关于FllterChain请看官方解释security-filter-chain

另外关于PRE_AUTH_FILTER拦截器的官方解释preauth，我们在此就采取已经被可靠的验证系统验证过的流程即验证Token的合法性，我们看一下这个拦截器的bean设置

<b:bean id="preTokenAuthenticationFilter"
            class="com.will.security.token.PreRequestHeaderAuthenticationFilter">
            <b:property name="authenticationManager" ref="preAuthenticationManager" />
            <b:property name="authenticationFailureHandler" ref="authFailureHandler"/>
            <b:property name="principalRequestHeader" value="X-Auth-Token"/>
            <b:property name="continueFilterChainOnUnsuccessfulAuthentication" value="false" />
    </b:bean>
    
     <!-- PreAuthentication manager. -->
    <b:bean id="authFailureHandler" class="org.springframework.security.web.authentication.ForwardAuthenticationFailureHandler" >
         <b:constructor-arg value="/service/secure/admin/login/failed" />
    </b:bean>
    
    <b:bean id="preauthAuthProvider" class="org.springframework.security.web.authentication.preauth.PreAuthenticatedAuthenticationProvider">
        <b:property name="preAuthenticatedUserDetailsService">
            <b:bean id="userDetailsServiceWrapper"  class="org.springframework.security.core.userdetails.UserDetailsByNameServiceWrapper">
                <b:property name="userDetailsService" ref="tokenUserDetailsService"/>
            </b:bean>
        </b:property>
        <b:property name="userDetailsChecker">
            <b:bean id="tokenUserDetailsChecker" class="com.will.security.token.TokenUserDetailsChecker" />
        </b:property>
    </b:bean>
    <authentication-manager id="preAuthenticationManager">
         <authentication-provider ref="preauthAuthProvider" />
    </authentication-manager>

PreRequestHeaderAuthenticationFilter里，截取访问的request，然后获取上传的Token串，这里的Token串储存在“SM_UER”的header里，
代码如下：

public class PreRequestHeaderAuthenticationFilter extends
        AbstractCustomPreAuthenticatedProcessingFilter {

    private String principalRequestHeader = "SM_USER";
    private String credentialsRequestHeader;
    private boolean exceptionIfHeaderMissing = true;
    
    @Override
    protected Object getPreAuthenticatedCredentials(HttpServletRequest request) {
　　　　 /*获取principal信息*/
        String principal = request.getHeader(principalRequestHeader);

        if (principal == null && exceptionIfHeaderMissing) {
            // 对于request进行BadException处理
            request.setAttribute(WebAttributes.AUTHENTICATION_EXCEPTION, new BadCredentialsException("No pre-authenticated credentials found in request."));
           
            return "N/A";
        }

        return principal;
    }

    @Override
    protected Object getPreAuthenticatedPrincipal(HttpServletRequest request) {
        if (credentialsRequestHeader != null) {
            return request.getHeader(credentialsRequestHeader);
        }

        return "N/A";
    }

    public void setPrincipalRequestHeader(String principalRequestHeader) {
        Assert.hasText(principalRequestHeader,
                "principalRequestHeader must not be empty or null");
        this.principalRequestHeader = principalRequestHeader;
    }

    public void setCredentialsRequestHeader(String credentialsRequestHeader) {
        Assert.hasText(credentialsRequestHeader,
                "credentialsRequestHeader must not be empty or null");
        this.credentialsRequestHeader = credentialsRequestHeader;
    }

    /**
     * Defines whether an exception should be raised if the principal header is missing.
     * Defaults to {@code true}.
     *
     * @param exceptionIfHeaderMissing set to {@code false} to override the default
     * behaviour and allow the request to proceed if no header is found.
     */
    public void setExceptionIfHeaderMissing(boolean exceptionIfHeaderMissing) {
        this.exceptionIfHeaderMissing = exceptionIfHeaderMissing;
    }
}

如果需要详细了解认证流程建议查看PreAuthenticatedAuthenticationProvider的源码，对于provider的配置也就一目了然了

TokenUserDetailsService的代码如下

public class TokenUserDetailsService implements UserDetailsService {

    private TokenManager tokenManager;
    
    @Override
    public UserDetails loadUserByUsername(String token)
            throws UsernameNotFoundException {
        if (token.equalsIgnoreCase("N/A")) {
            return null;
        }
        
        return tokenManager != null ? tokenManager.getUserDetails(token) : null;
    }
    
    public void setTokenManager(TokenManager tm) {
        this.tokenManager = tm;
    }

}

TokenManager负责Token的生成，验证以及删除等等操作

public interface TokenManager {

    /**
     * Creates a new token for the user and returns its {@link TokenInfo}.
     * It may add it to the token list or replace the previous one for the user. Never returns {@code null}.
     */
    TokenInfo createNewToken(UserDetails userDetails);

    /** Removes all tokens for user. */
    //void removeUserDetails(UserDetails userDetails);

    /** Removes a single token. */
    UserDetails removeToken(String token);

    /** Returns user details for a token. */
    UserDetails getUserDetails(String token);
    
    /** Returns user details for a username. */
    UserDetails getUserDetailsByUsername(String username);

    /** Returns a collection with token information for a particular user. */
    Collection<TokenInfo> getUserTokens(UserDetails userDetails);
    
    
    Boolean validateToken(String token);
    
}

我们可以根据自己的需要比如借助Redis做缓存，或者使用JWT等等，具体可实现自己的TokenManager