为啥我的nginx反向代理跨域问题Access-Control-Allow-Origin设置无效？

为啥我的nginx反向代理跨域问题Access-Control-Allow-Origin设置无效？

server {
    listen 80;
    server_name your.domain.com;

    location / {

        # 添加跨域头
        add_header Access-Control-Allow-Origin '*';
        add_header Access-Control-Allow-Credentials true;
        add_header Access-Control-Allow-Methods 'GET, POST, OPTIONS, PUT, DELETE';
        add_header Access-Control-Allow-Headers 'Content-Type, Authorization, X-Requested-With';

        # 处理 OPTIONS 请求
        if ($request_method = 'OPTIONS') {
            add_header Content-Length 0;
            add_header Content-Type text/plain;
            return 204;
        }
        proxy_pass http://backend_server;
        # 保持原有 Host
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

不管怎么设置Access-Control-Allow-Origi还是报错