Push to GitHub from Jenkins job

Jenkinsfile

node {
    // This step utilizes the Workspace Cleanup Plugin: https://wiki.jenkins.io/display/JENKINS/Workspace+Cleanup+Plugin
    step([$class: 'WsCleanup'])  
}
node {
    sshagent (credentials: ['<< insert credentialsId here >>']) {
        sh("git clone << your repo here, should be "git@..." like git@github.com:username/reponame.git >>")
    }
}
node {
    // Make whatever changes you want to the files in the cloned repo here. For example, update a certain file with a the latest for the purpose of backing it up.
    //  The curl command below is an example, and it's what I am using for backing up ranger policies into GitHub.
    // sh "curl -X GET --header 'text/json' -H 'Content-Type: text/json' -u user:pass 'http://172.111.92.43:6080/service/plugins/policies/exportJson' > reponame/ranger-policies/policies.json"
}
node {
    sshagent (credentials: ['<< insert credentialsId again here >>']) {
        // "git add", "git commit", and "git push" your changes here. You may have to cd into the repo directory like I did here because the current working directory is the parent directory to the directory that contains the actual repo, created by "git clone" earlier in this Jenkinsfile.
        sh("(cd reponame && git add ranger-policies/policies.json)")
        sh("(cd reponame && git commit -m 'daily backup of ranger-policies/policies.json')")
        sh('(cd reponame && git push git@github.com:username/reponame.git)')
    }
}