Manage private composer repos during docker build

Dockerfile

FROM php:7.2.26-fpm-stretch
# Fixed version with OS Debian strech for the issue here explained
# https://github.com/docker-library/php/issues/865

# Set defaults for variables used by run.sh
ENV COMPOSER_HOME=/root/.composer  
# Create Composer directory (cache and auth files) & Get Composer
RUN mkdir -p $COMPOSER_HOME \
    && curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer

WORKDIR /var/www

COPY composer.json composer.lock /var/www/

# the following variable exists only during build-time
# pass the correct value during build:
#     $ docker build --build-arg github_token=abcdef123456 # [...]
#
ARG GITHUB_TOKEN=abcdef123456
# Avoid the following line, because leave the environment variable
# in the final image
# ENV GITHUB_TOKEN=$github_token
# The secure way to do it is to prepend the command with the variable definition:
ENV COMPOSER_ALLOW_SUPERUSER=1
RUN echo "Running composer"  \
	&& composer global require hirak/prestissimo \
	&& composer global config github-oauth.github.com "$GITHUB_TOKEN" \
	&& composer install --prefer-dist --no-scripts --no-dev \ 
	&& rm -rf /root/.composer 


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