CORS实现跨域时授权问题（401错误）的解决

前几天的文章Spring通过CROS协议解决跨域问题 中提到了如何解决跨域问题的基本思路,解决了跨域请求时浏览器403错误。

Response to preflight request doesn't pass access control check:
No 'Access-Control-Allow-Origin' header is present on the requested resource.
Origin 'null' is therefore not allowed access. 
The response had HTTP status code 403

如果我们访问的资源是不需要授权的，也就是在HTTP请求头中不包含authentication头那么以上做法就足够了。但是如果该资源是需要权限验证的，那么这个时候跨域请求的预检测option请求，由于不会携带身份信息而被拒绝。浏览器会报出401错误。错误信息如下：

Failed to load resource:
the server responded with a status of 401 (Unauthorized)
XMLHttpRequest cannot load http://localhost/api/test.
Response for preflight has invalid HTTP status code 401

既然知道了问题的原因，答案也就很容易得出：对需要进行跨域请求的资源（api），当服务端检测到是OPTONS请求时候统统放行，给出HTTP.OK(200)的状态和必要的响应头，哪怕它是不带身份信息的。
这个问题既可以通过编写对应的后端代码实现，也可以通过设置服务器配置文件实现。也就是如何设置响应头和返回200状态码的办法了。

shiro中可以在自己实现的身份验证filter中加入以下代码：

  @Override
    protected boolean preHandle(ServletRequest servletRequest, ServletResponse servletResponse) throws Exception {
 HttpServletRequest request = (HttpServletRequest) servletRequest;
 HttpServletResponse response = (HttpServletResponse) servletResponse;
 if(request.getMethod().equals(RequestMethod.OPTIONS.name()))
 {
     response.setStatus(HttpStatus.OK.value());
     return false;
 }
 return super.preHandle(request, response);
    }

CorsFilter
org.apache.catalina.filters.CorsFilter
     
     
CorsFilter
/*
     

add_header 'Access-Control-Allow-Methods' 'GET,OPTIONS,PUT,DELETE' always;
add_header 'Access-Control-Allow-Credentials' 'true' always;
add_header 'Access-Control-Allow-Origin' '$http_origin' always;
add_header 'Access-Control-Allow-Headers' 'Authorization,DNT,User-Agent,Keep-Alive,Content-Type,accept,origin,X-Requested-With' always;

if ($request_method = OPTIONS ) {
    return 200;
}

Header always set Access-Control-Allow-Origin "http://waffle"
Header always set Access-Control-Allow-Methods "POST, GET, OPTIONS"
Header always set Access-Control-Allow-Credentials "true"
Header always set Access-Control-Allow-Headers "Authorization,DNT,User-Agent,Keep-Alive,Content-Type,accept,origin,X-Requested-With"

RewriteCond %{REQUEST_METHOD} OPTIONS
RewriteRule ^(.*)$ $1 [R=200,L]

$http({
  method: 'POST',
  url: scope.webdav.url,
  withCredentials: true,
  headers: {
    Authorization: 'Basic ' + btoa(user + ':' + password),
    'Content-Type': 'application/vnd.google-earth.kml+xml; charset=utf-8'
  },
  data: getKml()
})