Ensure SSH keys in Jenkins slave

.ciconfig

pipeline {
    agent { dockerfile true }
    environment {
        npm_config_cache = 'npm-cache'
    }
    stages {
        stage('Install') {
            steps {
                echo 'Ensure SSH keys'
                // set the credentials to be able to access private repos
                withCredentials([file(credentialsId: 'sshkey', variable: 'SSHKEY')]) {
                    sh 'mkdir -p ~/.ssh'
                    sh 'cp $SSHKEY ~/.ssh/id_rsa'
                    sh 'chmod 600 ~/.ssh/id_rsa'
                    sh 'echo \'Host github.com\n     StrictHostKeyChecking no\' > ~/.ssh/config'
                }
                echo 'Install'
                sh 'node --version'
                sh 'npm --version'
                sh 'npm i'
            }
        }
        stage('Unit tests') {
           steps {
                sh 'npm t'
           }
        }
    }
}