Proper Current user pass-through for docker container

Dockerfile

FROM debian

RUN apt-get update && apt-get install -y sudo acl

ARG USER_NAME
ARG USER_UID
ARG USER_GID

# Reuse existing UID if present; otherwise create user and group
RUN existing_user=$(getent passwd "${USER_UID}" | cut -d: -f1) && \
    if [ -n "$existing_user" ]; then \
        if [ "$existing_user" != "${USER_NAME}" ]; then \
            usermod -l "${USER_NAME}" "$existing_user" && \
            groupmod -n "${USER_NAME}" "$existing_user"; \
        fi; \
    else \
        if ! getent group "${USER_GID}" >/dev/null; then \
            groupadd -g "${USER_GID}" "${USER_NAME}"; \
        fi && \
        useradd -m -u "${USER_UID}" -g "${USER_GID}" -s /bin/bash "${USER_NAME}"; \
    fi

# Give them passwordless sudo 
RUN echo ${USER_NAME} ALL=\(root\) NOPASSWD:ALL > /etc/sudoers.d/${USER_NAME} \
    && chmod 0440 /etc/sudoers.d/${USER_NAME}

USER ${USER_NAME}

run.sh

#!/bin/bash

CONTAINER_TAG="user_passthrough"

# Fail on any error, undefined variable, or failed pipe command
set -euo pipefail

# Build and pass our current user's uid, gid and username
echo "Building container..."
docker build \
    --build-arg USER_UID=$(id -u) \
    --build-arg USER_GID=$(id -g) \
    --build-arg USER_NAME=$(whoami) \
    -t ${CONTAINER_TAG} .

echo "Running container..."
docker run -it \
    -v $PWD:/workspaces/nucleus-infra-bootstrap \
    ${CONTAINER_TAG} bash