Nginx proxy_pass from route without trailing slash - nginx

Question

I would like to configure Nginx to have one route on my domain proxy to another URL. More specifically, I'd like my.domain.com/special_route to proxy to another.domain.com and for the URL to remain unchanged in the address bar. For example, I'd like my.domain.com/special_route/some_path to proxy to another.domain.com/some_path, while the URL remains unchanged.
This is the configuration I have added so far:
set $another_url https://another.domain.com;
location ~ /special_route(/?.*)$ {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
add_header 'Access-Control-Allow-Origin' '*';
proxy_pass $another_url$1;
}
It appears to work mostly as intended with one notable exception. my.domain.com/special_route/some_path works, my.domain.com/special_route/ also works. However, my.domain.com/special_route (without the trailing slash) does not work. It appears to proxy to another.domain.com/special_route.
What do I need to change or add to my config to get the base route working without the trailing slash?

Answer 1

When the $1 is empty, it becomes just proxy_pass http://upstream which means the url is passed in full to the backend (/special_route).
The variable need to be updated to / in such cases. This is one possible method:
# tip: it should start with ^/ unless you do mean
# to allow accessing /thing/special_route in the same fashion
location ~ ^/special_route(/?.*)$ {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
# another tip: unless you know what you're doing,
# don't use $proxy_add_x_forwarded_for. Just use $remote_addr
# otherwise people may be able to fake their ip in some cases
proxy_set_header X-Forwarded-For $remote_addr;
add_header 'Access-Control-Allow-Origin' '*';
set $proxy_url $1;
if ($proxy_url = '') {
set $proxy_url /;
}
proxy_pass $another_url$proxy_url;
}