Nginx auth_basic not working for a specific url - authentication

Question

I would like to password protect one of the URLs I have and I am trying to do it with:
location /about/payment {
auth_basic "secured site";
auth_basic_user_file /var/www/my.passwd;
}
The problem is that I am asked for the username and paasword. AS soon as I put the right username and password, I am getting a 404 Error with this log:
*55268 open() "/var/www/mysite.com/deployment/web/about/payment" failed (2: No such file or directory), client: 172.16.0.53, server: ~^(?<branch>\w+)\.mysite\.dev$, request: "GET /about/payment HTTP/1.1", host: "deployment.mysite.dev"
EDIT:
The entire nginx conf file is here
server {
listen 80;
access_log ...;
error_log ...;
server_name ~^(?<branch>\w+)\.mysite\.dev$ ~^(?<branch>\w+)\.mysite\.com$;
root /var/www/git/branches/mysite.com/$branch/web;
location /about/payment {
auth_basic "secured site";
auth_basic_user_file /var/www/mysite.passwd;
}
# strip app_eudev.php/ prefix if it is present
rewrite ^/app_eudev\.php/?(.*)$ /$1 permanent;
# remove trailing slash
rewrite ^/(.*)/$ /$1 permanent;
# sitemap rewrite
rewrite ^/sitemap_(.*)$ /sitemap/$1 last;
location / {
try_files $uri #symfonyapp;
}
location #symfonyapp {
rewrite ^(.*)$ /app_eudev.php/$1 last;
}
location /var/www/dms/ {
internal;
alias /var/www/dms/;
}
location #htmlimages {
root /var/www/dms/;
}
location ~ /html/.*\.(png|gif|jpg|pdf)$ {
root ...;
try_files $uri #htmlimages;
}
location /files {
root ...;
}
location /assets {
root ...;
}
location /img {
root ...
}
location ~ \.php(/|$) {
fastcgi_pass 127.0.0.1:9001;
fastcgi_split_path_info ^(.+\.php)(/.*)$;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param HTTPS off;
}
}

Answer 1

When nginx find matching location that will process request it ignores any other location that could possibly match request.
In your case before you add auth, request to /about/payment was proceeded by location / which finally passed request to PHP. But as soon as you add location /about/payment request to that URL will be processed by this location which has no special directives so nginx will try to serve static files.
You should add directives that pass request to PHP, in this case it's really simple:
location /about/payment {
auth_basic "secured site";
auth_basic_user_file /var/www/my.passwd;
root ...;
try_files $uri #symfonyapp;
}

Answer 2

E.g. for Wordpress site, I wanna lock the URL
location ~* /block-url/ {
auth_basic "Internal Staging Site";
auth_basic_user_file /etc/nginx/.htpasswd;
try_files $uri $uri/ /index.php?$args; # Most important!
}