vars/gitSSHCheckout.groovy

def call(body) {
  // evaluate the body block, and collect configuration into the object
  def config = [:]
  body.resolveStrategy = Closure.DELEGATE_FIRST
  body.delegate = config
  body()

  def targetDir = config.targetDir ?: "./"
  def port = config.port ?: "29418"

  checkout(
    scm: [
      $class: 'GitSCM',
      branches: [[name: "${config.branch}"]],
      extensions: [
        [$class: 'CleanCheckout'],
        [$class: 'RelativeTargetDirectory', relativeTargetDir: "${targetDir}"]
      ],
      userRemoteConfigs: [[
        credentialsId: "${config.credentialsId}",
        name: 'origin',
        url: "ssh://${config.credentialsId}@${config.host}:${port}/${config.project}.git"
      ]]
    ]
  )
}