Nginx proxy pass directly to Main UI page

I like to proxy my external subdomain directly to a specific user page and then restrict access to a set of predefined pages. I played around with a number of different configurations for location blocks but could not get it to work. Could not find anything in search either.

any help is very much appreciated.

here is what I like to achieve:
“” proxy to “”
protected via nginx certs and basic auth so that a user only has access to “” = “XX*”