usage example at https://gist.github.com/MarianoGnu/8867253ba5df00c87a599745d25aa55c

http_request.gd

extends HTTPRequest

var last_response = null

func _ready():
	# connect signal to catch body
	self.connect("request_completed", self, "_on_HTTPRequest_request_completed")

func request_url(url):
	self.request(url) # request to REST API
	# wait until request finishes,
	# _on_HTTPRequest_request_completed will be called when this happens too
	yield(self, "request_completed")
	# wait an extra frame to be sure last_response is loaded
	yield(get_tree(), "idle_frame")
	# return last_response as dictionary or array, depending on response
	return last_response
	
func _on_HTTPRequest_request_completed( result, response_code, headers, body ):
	last_response = parse_json(body.get_string_from_utf8())