UWSGI not receiving custom headers from nginx server - nginx

Question

The goal is for nginx server to pass a custom request header called X-PA-AUTH_TOKEN to the uwsgi server. Below is the server block in nginx.conf file.
server {
listen 9390 default_server;
server_name _;
location / {
include uwsgi_params;
uwsgi_pass_request_headers on;
uwsgi_pass unix:/run/uwsgi/irm.sock;
uwsgi_pass_header X-PA-AUTH_TOKEN;
if ($request_method = 'OPTIONS') {
add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
#
# Custom headers and headers various browsers *should* be OK with but aren't
#
add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,X-PA-AUTH_TOKEN';
#
# Tell client that this pre-flight info is valid for 20 days
#
add_header 'Access-Control-Max-Age' 1728000;
add_header 'Content-Type' 'text/plain; charset=utf-8';
add_header 'Content-Length' 0;
add_header 'X-PA-AUTH_TOKEN' '0';
return 204;
}
if ($request_method = 'POST') {
add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,X-PA-AUTH_TOKEN';
add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range,X-PA-AUTH_TOKEN';
}
if ($request_method = 'GET') {
add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,X-PA-AUTH_TOKEN';
add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range,X-PA-AUTH_TOKEN';
}
}
}
The uwsgi server receives the conventional headers like 'Content-Type' just fine from the nginx server.
But, the uwsgi server is still not receiving the custom request header X-PA-AUTH_TOKEN from the nginx server when, for example, a POST request is made.
What am I doing wrong here?

Answer 1

I believe by default nginx marks headers with underscores (X-PA-AUTH_TOKEN) as invalid so they get blocked. You can either enable underscores_in_headers: on; in nginx config (docs here) or simply rename your header to be X-PA-AUTH-TOKEN.
Note however that if you enable underscores_in_headers, what you actually receive on the flask side will be renamed to X-Pa-Auth-Token, so i guess it's better to simply rename the header in the first place and not bother with nginx setting.