import jenkins.model.Jenkins
import hudson.security.HudsonPrivateSecurityRealm
import hudson.security.FullControlOnceLoggedInAuthorizationStrategy

def jenkins = Jenkins.instance
def realm = new HudsonPrivateSecurityRealm(false)
if (realm.getAllUsers().isEmpty()) {
    realm.createAccount("admin", "admin")
}
jenkins.setSecurityRealm(realm)

def strategy = new FullControlOnceLoggedInAuthorizationStrategy()
strategy.setAllowAnonymousRead(true)
jenkins.setAuthorizationStrategy(strategy)

jenkins.save()