Question

How do I enable CORS on Ubuntu 20.04 with nginx?

Hello!

I am having a thus far unsurmountable issue with enabling my website, hosted at /var/www/html/, from sending a json object via an ajax post request through a hmtl file to a plumber api I have listening at droplet-ip:3000/myApi. I have configured my plumber api config file in etc/nginx/sites-available/ as follows:

location /myApi/ { 
  proxy_pass http://localhost:3000/; 
  proxy_http_version 1.1; 
  proxy_set_header Upgrade $http_upgrade; 
  proxy_set_header Connection 'upgrade'; 
  proxy_set_header Host $host; 
  proxy_cache_bypass $http_upgrade; 
  add_header 'Access-Control-Allow-Origin' '*'; 
  add_header 'Access-Control-Allow-Credentials' 'true'; 
  add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS'; 
  add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
}

I have my plumber.R file configured with

"Access-Control-Allow-Origin", "*"

And I have a firewall enabled for this droplet with port 8000 and 3000 tcp and udp access.

The error I am still receiving is:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://droplet-ip:3000/myApi. (Reason: CORS request did not succeed). Status code: (null).

Any help here is so very much appreciated! Cheers.

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KFSys
Site Moderator
Site Moderator badge
• January 4, 2023

Hi @friendlylightseagreeneel,

I’ve read a bit more on the subject of passing some values to a reverse proxy API. A few times I’ve seen the following examples:

if ( $request_method !~ ^(GET|POST|HEAD|OPTIONS|PUT|PATCH|DELETE)$ ) {
    return 444;
}
    
set $origin $http_origin;

if ($origin !~ '^https?://(subdom1|subdom2)\.yourdom\.zone$') {
    set $origin 'https://default.yourdom.zone';
}

if ($request_method = 'OPTIONS') {

    add_header 'Access-Control-Allow-Origin' "$origin" always;
    add_header 'Access-Control-Allow-Methods' 'GET, POST, PATCH, PUT, DELETE, OPTIONS' always;
    add_header 'Access-Control-Allow-Headers' 'Content-Type, Accept, Authorization' always;
    add_header 'Access-Control-Allow-Credentials' 'true' always;

    add_header Access-Control-Max-Age 1728000;
    add_header Content-Type 'text/plain charset=UTF-8';
    add_header Content-Length 0;
    return 204;
}
    
if ($request_method ~ '(GET|POST|PATCH|PUT|DELETE)') {
    add_header Access-Control-Allow-Origin "$origin" always;
    add_header Access-Control-Allow-Methods 'GET, POST, PATCH, PUT, DELETE, OPTIONS' always;
    add_header Access-Control-Allow-Headers 'Content-Type, Accept, Authorization' always;
    add_header Access-Control-Allow-Credentials true always;
}

Of course this includes all the necessary options needed. What you can use is :

if ($request_method ~ '(GET|POST|PATCH|PUT|DELETE)') {
    add_header Access-Control-Allow-Origin "$origin" always;
    add_header Access-Control-Allow-Methods 'GET, POST, PATCH, PUT, DELETE, OPTIONS' always;
    add_header Access-Control-Allow-Headers 'Content-Type, Accept, Authorization' always;
    add_header Access-Control-Allow-Credentials true always;
}

An alternative would be:

    set $cors_origin "";
    set $cors_cred   "";
    set $cors_header "";
    set $cors_method "";

    if ($http_origin ~ '^https?://(localhost|mywebsite\.com)$') {
            set $cors_origin $http_origin;
            set $cors_cred   true;
            set $cors_header $http_access_control_request_headers;
            set $cors_method $http_access_control_request_method;
    }

    add_header Access-Control-Allow-Origin      $cors_origin;
    add_header Access-Control-Allow-Credentials $cors_cred;
    add_header Access-Control-Allow-Headers     $cors_header;
    add_header Access-Control-Allow-Methods     $cors_method;

    location /myApi/ { 
      proxy_pass http://localhost:3000/; 
      proxy_http_version 1.1; 
      proxy_set_header Upgrade $http_upgrade; 
      proxy_set_header Connection 'upgrade'; 
      proxy_set_header Host $host; 
      proxy_cache_bypass $http_upgrade; 
  }

Hope that helps!

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