docker-magento/compose/bin/setup-composer-auth

#!/bin/bash
set -o errexit

MAGENTO_USERNAME_PROP="http-basic.repo.magento.com.username"
MAGENTO_PASSWORD_PROP="http-basic.repo.magento.com.password"
hash composer 2>/dev/null && IS_COMPOSER_ON_HOST=true

if [ $IS_COMPOSER_ON_HOST ]; then
    PUBLIC_KEY="$(composer config --global $MAGENTO_USERNAME_PROP 2>/dev/null)"
    PRIVATE_KEY="$(composer config --global $MAGENTO_PASSWORD_PROP 2>/dev/null)"
fi

if [ -z "$PUBLIC_KEY" ] || [ -z "$PRIVATE_KEY" ]; then
    exec < /dev/tty
    echo
    echo "    Authentication required (repo.magento.com, public_key and private_key):"
    read -r -p "        Username: " PUBLIC_KEY
    read -r -p "        Password: " PRIVATE_KEY
    echo
    exec <&-
fi

if [ -z "$PUBLIC_KEY" ] || [ -z "$PRIVATE_KEY" ]; then
    echo "Please setup Composer auth for repo.magento.com to continue." && exit 1
fi

bin/clinotty composer config --global http-basic.repo.magento.com "$PUBLIC_KEY" "$PRIVATE_KEY"

echo "Composer auth has been setup."