Andrey Shatokhin

location /folder {
        proxy_pass https://backend;
        proxy_ssl_server_name on;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Port $server_port;
        proxy_set_header Connection "upgrade";
      }

merge_slashes off;
if ($request_uri ~* "\/\/") {
  rewrite ^/(.*)      $scheme://$host/$1    permanent;
}

if ($host != 'demo.ru') { return 301 https://demo.ru$request_uri;}

if ($scheme = 'http') { return 301 https://demo.ru$request_uri;}