here is the relevant code for apache:

<VirtualHost *:80>
ServerAdmin admin@unogs.com
ServerName unogs.com
ServerAlias *.unogs.com
ProxyRequests Off
ProxyVia Off
<Proxy *>
        Order deny,allow
        Allow from all
</Proxy>
# edit the next line if you use https
RequestHeader set X-Forwarded-Proto "http"

RewriteEngine On
AllowEncodedSlashes On #important for the admin interface on nodebb
RewriteCond %{REQUEST_URI}  ^/forum/socket.io            [NC]
RewriteCond %{QUERY_STRING} transport=websocket    [NC]
RewriteRule /forum/(.*)           ws://127.0.0.1:4567/forum/$1 [P,L]
ProxyPass /forum/ http://127.0.0.1:4567/forum/ nocanon
ProxyPassReverse /forum/ http://127.0.0.1:4567/forum/

DocumentRoot /mydocroot #where the rest of the site lives
</VirtualHost>

The only real differences between this and the documentation are 'AllowEncodedSlashes On' which is necessary to get the admin interface working. and I have appended the '/' with '/forum/' to make only the forum sub directory reverse proxied.

Next, to get the sub directory working you need to change your nodebb config.json file to the following:

{
    "url": "http://unogs.com/forum",
    "secret": "itsasecret",
    "database": "mongo",
    "port": "4567",
    "mongo": {
        "host": "127.0.0.1",
        "port": "27017",
        "username": "xxx",
        "password": "xxx",
        "database": "xxx"
    }
}

I'm ashamed to say how long it took me to figure this out, but as you can see its working now.

-admin