NGINX CORS Issues - ajax

Question

There is a server with NGINX 1.16, which is used to upload files through AJAX
Here are the configuration settings of the NGINX file
location ~ \.php$ {
include snippets/fastcgi-php.conf;
#
# With php-fpm (or other unix sockets):
fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;
# With php-cgi (or other tcp sockets):
#fastcgi_pass 127.0.0.1:9000;
if ($request_method = "OPTIONS") {
add_header Access-Control-Allow-Origin 'http://myserver.com';
add_header Access-Control-Allow-Credentials false;
add_header Access-Control-Allow-Methods 'DELETE,GET,OPTIONS,POST,PUT';
add_header Access-Control-Allow-Headers 'Accept,Authorization,Cache-Control,Content-Type,DNT,If-Modified-Since,Keep-Alive,Origin,User-Agent,X-Requested-With,X-Token-Auth,X-Mx-ReqToken,X-Requested-With';
add_header 'Access-Control-Max-Age' 1728000;
add_header 'Content-Type' 'text/plain charset=UTF-8';
add_header 'Content-Length' 0;
return 204;
}
add_header Access-Control-Allow-Origin 'http://myserver.com';
add_header Access-Control-Allow-Credentials true;
add_header Access-Control-Allow-Methods 'DELETE,GET,OPTIONS,POST,PUT';
add_header Access-Control-Allow-Headers 'Accept,Authorization,Cache-Control,Content-Type,DNT,If-Modified-Since,Keep-Alive,Origin,User-Agent,X-Requested-With,X-Token-Auth,X-Mx-ReqToken,X-Requested-With';
}
Here are the test results for CURL
When you try to upload a file, a CORS error is displayed in the console
Maybe someone came across a similar behavior when СORS is turned on on the server, but an error pops up anyway?
UPD: It has also been noticed that headers are not displayed in the browser. There is an assumption that this is the reason, but then how to “force” the server to give headers?

Answer 1

add_header Access-Control-Allow-Origin 'http://myserver.com'; is wrong in your setting.
location / {
if ($request_method = 'OPTIONS') {
add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
#
# Custom headers and headers various browsers *should* be OK with but aren't
#
add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
#
# Tell client that this pre-flight info is valid for 20 days
#
add_header 'Access-Control-Max-Age' 1728000;
add_header 'Content-Type' 'text/plain; charset=utf-8';
add_header 'Content-Length' 0;
return 204;
}
if ($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';
add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
}
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';
add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
}
}