Supply Git username/password via environment variables, plus sample Jenkinsfile

git-credential-env.sh

#!/bin/sh
[ "${DEBUG:-0}" = "1" ] && set -x

SCRIPT="$0"
command -v readlink 2>/dev/null 1>/dev/null && SCRIPT="$(readlink -f "$0")"

if [ "$1" = "--install" ] ; then
    git config --global credential.helper "/bin/sh $SCRIPT"
    exit $?
fi

printf "username=%s\n" "$GIT_USERNAME"
printf "password=%s\n" "$GIT_PASSWORD"

Jenkinsfile

node('node-label') {
    stage('Checkout') {
        scm checkout
    }

    stage('Tag') {
        sh 'git tag my-tag'
        sh 'sh git-credential-env.sh --install'

        withCredentials([[
            $class: 'UsernamePasswordMultiBinding',
            credentialsId: 'my-git-credential-id',
            usernameVariable: 'GIT_USERNAME',
            passwordVariable: 'GIT_PASSWORD'
        ]]) {
            sh 'git push origin my-tag'
        }
    }
}