Jenkins Groovy enable security and create a user in groovy script

groovy-create-user.md

This is a snippet that will create a new user in jenkins and if security has been disabled , it will enable it :)

import jenkins.model.*
import hudson.security.*

def instance = Jenkins.getInstance()

def hudsonRealm = new HudsonPrivateSecurityRealm(false)
hudsonRealm.createAccount("MyUSERNAME","MyPASSWORD")
instance.setSecurityRealm(hudsonRealm)
instance.save()

Bonus: Add the created user as admin for jenkins: what if you want that user to be like admin of jenkins who can access anything.. no problem..just add following lines right above the 'instance.save()' statement and run :)

def strategy = new GlobalMatrixAuthorizationStrategy()
strategy.add(Jenkins.ADMINISTER, "myUSERNAME")
instance.setAuthorizationStrategy(strategy)

How to modify this script to this user to a specific existing group in Jenkins?