Nginx doesn’t seem to pass any additional custom header to $_SERVER variable. To make this happen you need to:
1. First the custom http header sending out (from your REST client) need to use dash instead of underscore, for example “HTTP-X-REST-USERNAME”.
2. On the server side, in your fastcgi_params file (/etc/nginx/fastcgi_params) add this:
fastcgi_param HTTP_X_REST_USERNAME $http_x_rest_username;
3. Restart server you will see $_SERVER[‘HTTP_X_REST_USERNAME’] inside php land.