curl is a tool for interacting with URLs on the command line, e.g.
curl https://curl.haxx.se/
returns the content of the curl website home page.
Preceded by a hyphen, can be specified all together, e.g.
curl -vdX POST https://curl.haxx.se/
v – verbose
X <method> – specify that request method <method> is to be used
GET is the default method. curl -vX GET will tell you that X GET is unnecessary!
d – send a Content-Length: 0 header
By default this doesn't happen, so curl -X POST will return an HTTP 411 if the service doesn't support POST requests with an empty message body