Slightly tighter CORS config for nginx

cors-nginx.conf

#
# Slightly tighter CORS config for nginx
#
# A modification of https://gist.github.com/1064640/ to include a white-list of URLs
#
# Despite the W3C guidance suggesting that a list of origins can be passed as part of
# Access-Control-Allow-Origin headers, several browsers (well, at least Firefox) 
# don't seem to play nicely with this.
#
# To avoid the use of 'Access-Control-Allow-Origin: *', use a simple-ish whitelisting 
# method to control access instead.
#
# NB: This relies on the use of the 'Origin' HTTP Header.

location / {

    if ($http_origin ~* (whitelist\.address\.one|whitelist\.address\.two)) {
        set $cors "true";
    }

    # Nginx doesn't support nested If statements. This is where things get slightly nasty.
    # Determine the HTTP request method used

    if ($request_method = 'OPTIONS') {
        set $cors "${cors}options";  
    }
    if ($request_method = 'GET') {
        set $cors "${cors}get";  
    }
    if ($request_method = 'POST') {
        set $cors "${cors}post";
    }

    if ($cors = "true") {
        # Catch all incase there's a request method we're not dealing with properly
        add_header 'Access-Control-Allow-Origin' "$http_origin";
    }

    if ($cors = "trueget") {
        add_header 'Access-Control-Allow-Origin' "$http_origin";
        add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,X-Mx-ReqToken,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
    }

    if ($cors = "trueoptions") {
        add_header 'Access-Control-Allow-Origin' "$http_origin";

        #
        # Om nom nom cookies
        #

        add_header 'Access-Control-Allow-Credentials' 'true';
        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,X-Mx-ReqToken,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
        
        #
        # 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 ($cors = "truepost") {
        add_header 'Access-Control-Allow-Origin' "$http_origin";
        add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,X-Mx-ReqToken,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';

    }
}