跨域The 'Access-Control-Allow-Origin' header contains multiple values '*, *', but only one is allowed.解决方案

使用Ajax跨域请求资源，Nginx作为代理，出现：The 'Access-Control-Allow-Origin' header contains multiple values '*, *', but only one is allowed 错误。

服务端允许跨域配置：

#region 设置允许跨域，允许复杂请求
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");
            if (HttpContext.Current.Request.HttpMethod == "OPTIONS")
            {
                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,PATCH,OPTIONS");
                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept, Authorization");
                //HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000");
                HttpContext.Current.Response.End();
            }
            #endregion

　　Nginx的配置：

 add_header 'Access-Control-Allow-Origin' '*';
        location / {
            if ($request_method = 'OPTIONS') {
            add_header Access-Control-Allow-Origin *;
                add_header Access-Control-Allow-Methods GET,POST,PUT,DELETE,PATCH,OPTIONS;
                return 200;
            }
            proxy_pass http://xx:8002/;
            #proxy_pass http://localhost:62249/;

　　contains multiple values "*" 意思就是设置了2次跨域，但是只有一个是允许的，移除其中的任意一个就好了。如果服务器设置了允许跨域，使用Nginx代理里面就不需要了（或者就不用使用Nginx了）