Configuration to use nginx as reverse proxy for Transmission BT with SSL/HTTP2 protected with auth

transmission-ssl

upstream transmission  {
      server 127.0.0.1:9091; #Transmission
}
server {
      listen 443 ssl http2;
      server_name example.com;
      auth_basic            "Server Restricted";
      auth_basic_user_file  /var/www/myWebSite/web/.htpasswd;
      
      # Path to the root of your installation
      error_log /var/www/myWebSite/logs/error.log;
      access_log /var/www/myWebSite/logs/access.log;
      
      ### SSL cert files ###
      ssl_certificate /var/www/myWebSite/ssl/advert.crt;
      ssl_certificate_key /var/www/myWebSite/ssl/advert.key;

      ### Add SSL specific settings here ###
      ssl_session_timeout 10m;
      
      ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
      ssl_ciphers ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv3:+EXP;
      ssl_prefer_server_ciphers on;
      
      location / {
          return 301 https://$server_name/transmission/;
      }
      
      location ^~ /transmission {
      
          proxy_set_header X-Real-IP $remote_addr;
          proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
          proxy_set_header Host $http_host;
          proxy_set_header X-NginX-Proxy true;
          proxy_http_version 1.1;
          proxy_set_header Connection "";
          proxy_pass_header X-Transmission-Session-Id;
          add_header   Front-End-Https   on;
      
          location /transmission/rpc {
              proxy_pass http://transmission;
          }
      
          location /transmission/web/ {
              proxy_pass http://transmission;
          }
      
          location /transmission/upload {
              proxy_pass http://transmission;
          }
      
          location /transmission/web/style/ {
              alias /usr/share/transmission/web/style/;
          }
      
          location /transmission/web/javascript/ {
              alias /usr/share/transmission/web/javascript/;
          }
      
          location /transmission/web/images/ {
              alias /usr/share/transmission/web/images/;
          }
          
          location /transmission/ {
              return 301 https://$server_name/transmission/web;
          }
      }

}

Did not work for me as written above, it would only show some text with none of the JavaScript or styles. Once I commented out the /style, /JavaScript, and /image parts it worked perfectly.

I've been at it for hours.

turns out you only needing this

proxy_pass_header   X-Transmission-Session-Id;

Here's my full confignuration

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name transmission.example.com;

    set $transmissionbt_web 127.0.0.1;

    ssl_certificate /etc/letsencrypt/live/transmission.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/transmission.example.com/privkey.pem;
    include /etc/letsencrypt/options-ssl-nginx.conf;
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;
    add_header Strict-Transport-Security "max-age=31536000" always;
    ssl_trusted_certificate /etc/letsencrypt/live/transmission.example.com/chain.pem;
    ssl_stapling on;
    ssl_stapling_verify on;

    proxy_hide_header X-Frame-Options; # this should allow iframe

    location / {
        proxy_read_timeout  300;
        proxy_set_header    Host                 $host;
        proxy_set_header    X-Forwarded-Proto    $scheme;
        proxy_set_header    X-Forwarded-Protocol $scheme;
        proxy_set_header    X-Real-IP            $remote_addr;
        proxy_pass_header   X-Transmission-Session-Id;
        proxy_set_header    X-Forwarded-Host     $host;
        proxy_set_header    X-Forwarded-Server   $host;
        proxy_set_header    X-Forwarded-For      $proxy_add_x_forwarded_for;
        proxy_pass          http://$transmissionbt_web:9091;
    }
}

I've attempted this solution but it doesn't work for me. The page initially loads, asks for login credentials and starts loading the interface but after a few moments, an error message appears indicating connection problems.

Checking the developer tools, I see a list of RPC calls attempts to the server but for which the UI never gets a response.

Have you guys had the same issue?

Thanks for the ready and working solution, @Zen3515!