git clone https://github.com/fogeytron/USPS-php-api-sample-app.git
curl -sS https://getcomposer.org/installer | php
php composer.phar install
You are on your own
https://www.usps.com/business/web-tools-apis/welcome.htm
Once you register you need to do call them and ask them to do two things on your account:
a. Switch your account to use the production servers
b. Change your account permissions to allow access to all the different APIs, by default you only have permissions to use Rate API