import jenkins.model.*
import com.cloudbees.plugins.credentials.*
import com.cloudbees.plugins.credentials.common.*
import com.cloudbees.plugins.credentials.domains.*
import com.cloudbees.plugins.credentials.impl.*
import com.cloudbees.jenkins.plugins.sshcredentials.impl.*
import hudson.plugins.sshslaves.*;

domain = Domain.global()
store = Jenkins.instance.getExtensionList('com.cloudbees.plugins.credentials.SystemCredentialsProvider')[0].getStore()

credId = 'jenkinsgithub'
username = 'jenkins'
privateKeyStr = "-----BEGIN RSA PRIVATE KEY-----\nMIIJ..."
privateKeySource = new BasicSSHUserPrivateKey.DirectEntryPrivateKeySource(privateKeyStr)
description = "Jenkins GitHub SSH Credentials"

privateKey = new BasicSSHUserPrivateKey(
        CredentialsScope.GLOBAL,
        credId,
        username,
        privateKeySource,
        "",
        description
)

store.addCredentials(domain, privateKey)