Nginx solves cross-domain problems (CORS)

foreword

CORS (Cross-Origin Resource Sharing) Cross-origin resource sharing is a mechanism that allows resources (such as html/js/web service) of the current domain (such as html/js/web service) to be accessed by scripts in other domains (domain), usually due to the same domain. The same-origin security policy browser prohibits such cross-origin requests. 
For example, when a.com requests resources from b.com, it involves cross-domain. At present, common cross-domain solutions are generally divided into the following categories:

• jsonp return value to solve get request
• iframe solves cross-domain access
• Nginx solves CORS

Nginx configuration

1 Simple configuration

server {
        listen       80;
        server_name  b.com;
        location /{ add_header 'Access-Control-Allow-Origin' 'http://a.com'; add_header 'Access-Control-Allow-Credentials' 'true'; add_header 'Access-Control-Allow-Methods' 'GET'; } }

• add_header: Authorize requests from a.com

• The second add_header: When this flag is true, whether it can be exposed in response to the request

• The third add_header: Specify the method of the request, which can be GET, POST, PUT, DELETE, HEAD 
  also supports wildcards, such as allowing requests from any domain:

server {
        listen 80;
        server_name b.com;
        location /{
            Access-Control-Allow-Origin: *
        }
    }

2 Advanced configuration

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

Because POST cross-domain requests will first send an OPTIONS sniffing request, all scenarios involve setting OPTIONS.