Jenkins create Folder with REST API in groovy skript

i am trying to create a Folder in Jenkins using a groovy script. For that i use an REST API call. My starting point is was basically a curl command:

curl -XPOST "http://userName:YourApiToken@JenkinsURL:Port/createItem?name=FolderName&mode=com.cloudbees.hudson.plugins.folder.Folder" -H "Content-Type:application/x-www-form-urlencoded" 

I got this from https://gist.github.com/marshyski/abaa1ccbcee5b15db92c and found later out that it also works if you put the user into the URL. Using this line in the Windows cmd works perfectly and generates me a new Folder in my Jenkins.

Now i try to do the same thing but from a groovy script. For that i use the following code:

import groovyx.net.http.*  def post = new URL("https://userName:YourApiToken@JenkinsURL:Port/createItem?name=FolderName&mode=com.cloudbees.hudson.plugins.folder.Folder").openConnection(); post.setRequestMethod("POST") post.setDoOutput(true) post.setRequestProperty("Content-Type", "application/x-www-form-urlencoded") def postRC = post.getResponseCode(); println(postRC); if(postRC.equals(200)) {     println(post.getInputStream().getText()); } 

I got this basically from Groovy built-in REST/HTTP client? (i have heard apache Http is deprecated)

Long story short i did not manage to create a folder with the given groovy script. I always get an 403 response (I run the script from windows cmd and inside jenkins with the script console). I also played around with Jenkins-crumb but that seems not necessary because the above cmd command already worked.

So the question is does anyone know what i am missing? why is the groovy script not working but the curl command is? Or has anyone a different approach on how to generate a Folder in Jenkins from a groovy script?