请教：nginx反向链接wss报错：Error during WebSocket handshake: Unexpected response code: 200

按照官方文档的示例，配置了nginx的wss反向链接。如下：

server{
    listen 443;
    listen :443;
    server_name  c.officedog.cn;
    root /alidata/www/cd;

    ssl on;
    ssl_certificate   /etc/nginx/cert/214354783860444.pem;
    ssl_certificate_key  /etc/nginx/cert/214354783860444.key;
    ssl_session_timeout 5m;  
    #ssl_ciphers ECDHE-RSA-AES128-GCM-SHA256:ECDHE:ECDH:AES:HIGH:!NULL:!aNULL:!MD5:!ADH:!RC4;  
    #ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ssl_session_cache shared:SSL:50m;
    ssl_protocols SSLv3 SSLv2 TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers ALL:!ADH:!EXPORT56:RC4 RSA: HIGH: MEDIUM: LOW: SSLv2: EXP;
    ssl_prefer_server_ciphers on;

    location /wss/ {
        proxy_pass http://120.24.64.45:8282/;  指向服务器socket服务器
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header X-real-ip $remote_addr;
        proxy_set_header X-Forwarded-For $remote_addr;
    }

    if ($scheme = http) {
        return 301 https://$server_name$request_uri;
    }

   #其他略

其中，http://120.24.64.45:8282/ 指向socket服务器。

protected $socket = 'websocket://120.24.64.45:8282';

测试一：客户端直接访问 ws://域名:8282 ，能否正常访问。
测试二：客户端访问 wss://域名 ，由nginx反向链接 ws://域名:8282 ，就报错了。报错内容如下:

WebSocket connection to 'wss://c.officedog.cn/' failed: Error during WebSocket handshake: Unexpected response code: 200

环境，阿里云CentOS7，PHP7，nginx。