Spring Security 实战干货：客户端OAuth2授权请求的入口

1. 前言

在Spring Security 实战干货：OAuth2第三方授权初体验一文中我先对OAuth2.0涉及的一些常用概念进行介绍，然后直接通过一个DEMO来让大家切身感受了OAuth2.0第三方授权功能。今天我们来一步一步分析这其中的机制。

2. 抓住源头

http://localhost:8082/oauth2/authorization/gitee

上面这个请求URL是我们在上一篇文章中提到的客户端进行第三方认证操作的起点，默认格式为{baseUrl}/oauth2/authorization/{clientRegistrationId}，其中clientRegistrationId代表着一个第三方标识，可以是微信、支付宝等开放平台，这里为gitee。用户点击了这个请求后就开始了授权之旅。假如大家都是从零开始的小白，肯定是要从这个入口来一步一步探寻其中的机制的。Spring Security一定是拦截到了/oauth2/authorization后才启用了OAuth2相关的处理逻辑。那就去抓住这个源头！从源码中搜索嘛！IDEA 快捷键CTRL SHIFT R 就可以全局搜索结果了。

IDEA 搜索结果

不出所料找到了三个地方，记下来一个一个看！

OAuth2AuthorizationRequestRedirectWebFilter

先来看第一个OAuth2AuthorizationRequestRedirectWebFilter，它实现了Spring Webflux的WebFilter接口，这显然是Webflux的东西，如果你用到Webflux的话这个会有用，但是不是现在我们用的。

DefaultOAuth2AuthorizationRequestResolver

第二个是干嘛的呢，从名称上看着是一个默认OAuth2授权请求解析器。有时候名称起的好就知道这个东西大致上干嘛的，不得不说优秀框架细节抓的很好。它实现了接口OAuth2AuthorizationRequestResolver:

public interface OAuth2AuthorizationRequestResolver {

   /**
    * 从HttpServletRequest对象中解析封装 OAuth2AuthorizationRequest
    */
   OAuth2AuthorizationRequest resolve(HttpServletRequest request);

   /**
    * 从HttpServletRequest对象以及clientRegistrationId中解析封装 OAuth2AuthorizationRequest
    */
   OAuth2AuthorizationRequest resolve(HttpServletRequest request, String clientRegistrationId);

}

也就是说当我们请求/oauth2/authorization时，DefaultOAuth2AuthorizationRequestResolver 会从/oauth2/authorization对应的HttpServletRequest中提取数据封装到OAuth2AuthorizationRequest请求对象中做进一步使用。

注意：/oauth2/authorization这个默认拦截标识也是可以自定义的。

OAuth2AuthorizationRequest

这里简单提一下OAuth2AuthorizationRequest 封装了我们上一文所描述的一些OAuth2相关概念参数，后续这个请求类我们会用到它。

public final class OAuth2AuthorizationRequest implements Serializable {
    private static final long serialVersionUID = 520L;
    private String authorizationUri;
    private AuthorizationGrantType authorizationGrantType;
    private OAuth2AuthorizationResponseType responseType;
    private String clientId;
    private String redirectUri;
    private Set<String> scopes;
    private String state;
    private Map<String, Object> additionalParameters;
    private String authorizationRequestUri;
    private Map<String, Object> attributes;
    // 其它方法略
}

OAuth2AuthorizationRequestRedirectFilter

就剩下这个线索了，一看到它继承了OncePerRequestFilter我就知道肯定是他了。甚至它的成员变量包含了用来解析OAuth2请求的OAuth2AuthorizationRequestResolver。到这里我们的路子就走对了，开始分析这个过滤器，下面是其核心过滤逻辑，这就是我们想要知道的OAuth2授权请求是如何被拦截处理的逻辑。

protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
      throws ServletException, IOException {

   try {
      OAuth2AuthorizationRequest authorizationRequest = this.authorizationRequestResolver.resolve(request);
      if (authorizationRequest != null) {
         this.sendRedirectForAuthorization(request, response, authorizationRequest);
         return;
      }
   } catch (Exception failed) {
      this.unsuccessfulRedirectForAuthorization(request, response, failed);
      return;
   }

   try {
      filterChain.doFilter(request, response);
   } catch (IOException ex) {
      throw ex;
   } catch (Exception ex) {
      // Check to see if we need to handle ClientAuthorizationRequiredException
      Throwable[] causeChain = this.throwableAnalyzer.determineCauseChain(ex);
      ClientAuthorizationRequiredException authzEx = (ClientAuthorizationRequiredException) this.throwableAnalyzer
         .getFirstThrowableOfType(ClientAuthorizationRequiredException.class, causeChain);
      if (authzEx != null) {
         try {
            OAuth2AuthorizationRequest authorizationRequest = this.authorizationRequestResolver.resolve(request, authzEx.getClientRegistrationId());
            if (authorizationRequest == null) {
               throw authzEx;
            }
            this.sendRedirectForAuthorization(request, response, authorizationRequest);
            this.requestCache.saveRequest(request, response);
         } catch (Exception failed) {
            this.unsuccessfulRedirectForAuthorization(request, response, failed);
         }
         return;
      }

      if (ex instanceof ServletException) {
         throw (ServletException) ex;
      } else if (ex instanceof RuntimeException) {
         throw (RuntimeException) ex;
      } else {
         throw new RuntimeException(ex);
      }
   }
}

doFilterInternal对应的流程如下：

OAuth2AuthorizationRequestRedirectFilter执行流程