vue+axios跨域post请求json格式问题

if ($request_method = 'OPTIONS') {
        add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Origin' 'http://localhost:8084';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
        add_header 'Access-Control-Max-Age' 1728000;
        add_header 'Content-Type' 'text/plain charset=UTF-8';
        add_header 'Content-Length' 0;
        return 204;
 }
 if ($request_method = 'POST') {
	      add_header 'Access-Control-Allow-Credentials' 'true';
        add_header 'Access-Control-Allow-Origin' 'http://localhost:8084';
        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' 'http://localhost:8084';
        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';
 }