LiteCart USPS Domestic Shipping Module

I need a USPS shipping add-on written for my LiteCart store that taps directly into the USPS Web Tools API and makes only domestic services available at checkout. Shoppers must be able to choose between USPS Ground Advantage and USPS Priority Mail, with the module passing the selected service, cost, and tracking number back into the order record.

The code has to slot into LiteCart’s existing extension structure, respect its event hooks, and include a simple admin screen where I can enter my USPS credentials, choose which of the two services to show, add handling fees, and toggle test or live mode. Clean PHP, no core edits—everything should install by copying the extension folder and running a single SQL patch for settings.

Acceptance criteria
• Module installs on a fresh LiteCart 2.5+ site without manual code changes
• Checkout displays only Ground Advantage and Priority Mail rates for U.S. destinations
• Orders placed with the module record the chosen service and cost in the database and admin panel
• Tracking number pulled from the API (or placeholder in test mode) is stored and visible to the buyer
• Clear README covering setup, API key acquisition, and common troubleshooting steps

If you have already built USPS integrations—or better, something for LiteCart—let me know. I’m ready to test on a staging store and push live as soon as it passes the criteria above.