Install composer:
curl -sS https://getcomposer.org/installer | /usr/local/php-7.3-httpd-2.4/bin/php

Update composer phar file
/usr/local/php-7.3-httpd-2.4/bin/php composer.phar selfupdate

Install something:
/usr/local/php-7.3-httpd-2.4/bin/php composer.phar require something/something

Update all installed:
/usr/local/php-7.3-httpd-2.4/bin/php composer.phar update

Or update only one package:
/usr/local/php-7.3-httpd-2.4/bin/php composer.phar something/something

Install AWS SDK:
/usr/local/php-7.3-httpd-2.4/bin/php -d memory_limit=-1 composer.phar require aws/aws-sdk-php

Install zipStream:
/usr/local/php-7.3-httpd-2.4/bin/php composer.phar require maennchen/zipstream-php