Invalid proxy_pass with $upstream variable

[rmartcas]

Checklist

• Have you pulled and found the error with jc21/nginx-proxy-manager:latest docker image?
  • Yes
• Are you sure you're not using someone else's docker image?
  • Yes
• Have you searched for similar issues (both open and closed)?
  • Yes

Describe the bug
After proxy host config update, custom locations fails.
Checking the proxy host number.conf before and after the update i can see this difference:

Before:

location ^~ /jenkins/ {
proxy_set_header Host $host;
proxy_set_header X-Forwarded-Scheme $scheme;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Real-IP $remote_addr;
proxy_pass http://127.0.0.01:8080/jenkins/;
}

After:

location ^~ /jenkins/ {
set $upstream http://127.0.0.01:8080/jenkins/;
proxy_set_header Host $host;
proxy_set_header X-Forwarded-Scheme $scheme;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Real-IP $remote_addr;
proxy_pass $upstream;
}

The same ocurrs with all other custom locations in the proxy host.

Nginx Proxy Manager Version
v2.9.9

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior

With the old proxy_pass http://.... works fine, but with variable set $upstream at begining of the ___location the proxy don't loads all related paths with custom locations

Screenshots

With new $upstream variable:

With old config or reventing the .conf manually and reloading nginx:

Operating System
Linux AMI

Additional context

Proxy host config files, before and after the last update.

proxy_conf_new.conf.txt
proxy_conf_old.conf.txt

[rmartcas]

Some info from stackoverflow that could help.

https://stackoverflow.com/questions/46230270/nginx-using-variable-in-proxy-pass-breaks-routing

[chaptergy]

Unfortunately I am not able to find a way which would allow both the usage of a variable for skipping ___domain caching and a working and generalizable path inclusion.
As the StackOverflow question also describes, proxy_pass expects a full url if it includes a variable, so no path is added to the host. This behaviour is also described in this article.
I have tried just adding the $request_uri variable to no avail, I've also tried using the regex ___location name which did not work and would not generalize well, and I've also tried a suggestion from a forum to use rewrite which did not work either.

Unless some fix is found which would fix both this issue and the one described in the commit, we would have to decide which issue is more relevant, either this one or the caching issue. I would personally say this issue is more relevant and to revert commit
6c1ae77. @jc21

Though the changes added in the commit could possibly also mitigate the issue raised in #633.

[chaptergy]

The changes have been reverted and should be included in the next release when it comes (2.9.13)

[kabadisha]

@shakamus & @chaptergy I took a look at this problem and think I have come up with a solution that works:
#2672
If you could take a look and test, that would be awesome :-)