@jtsimoes Thanks for letting me know and pointing me in the right direction.

@mango I'm looking for exactly this information as well. Searching for 'tag' in the list of all plugins yields no candidates. I feel like anything used on the NBB homepage should be part of the default install, but I found what you pictured above in my widgets

@ A Former User
I just wanted to note that the regex isn't necessary. I just installed and my working config is as follows:

  location /forum/ {
      proxy_pass http://172.17.2.3:4567;
      proxy_redirect off;
      proxy_set_header Host $http_host;
       proxy_set_header X-Forwarded-Host $host;
       proxy_set_header X-Forwarded-Server $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;
      proxy_set_header X-NginX-Proxy true;

      # Socket.IO Support
      proxy_http_version 1.1;
      proxy_set_header Upgrade $http_upgrade;
}

@Violing

I was able to make it work with /forum; no ^~ required. Given what @yariplus stated this seems relevant.
My conf:

location /forum/ {
      proxy_pass http://172.17.2.3:4567;
      proxy_redirect off;
      proxy_set_header Host $http_host;
       proxy_set_header X-Forwarded-Host $host;
       proxy_set_header X-Forwarded-Server $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;
      proxy_set_header X-NginX-Proxy true;

      # Socket.IO Support
      proxy_http_version 1.1;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection "upgrade";
   }

Indented lines are ones that I copied from my other blocks that weren't present in the suggested.