Farrah Abraham -- Signs 1st Endorsement Deal ... SIX FIGURES!!!

Farrah Abraham is following the Kim Kardashian Steps to Fame Playbook to perfection -- TMZ has learned the newly-minted porn star has just inked her first endorsement deal ... and the check has its fair share of zeroes at the end of it.

The Backdoor Teen Mom has signed on to endorse a product called Raspberry Tones ... which bills itself as a "diet and fat-loss" pill. We're told it wasn't the sex tape that caught the company's eye (ok, maybe a little) but rather the bikini pics of Farrah that surfaced last month.

According to our sources, Farrah loved the idea of endorsing a health product and couldn't pass up the payday ... which, we're told, is somewhere in the low six figures.

A rep for the company tells TMZ, "Farrah represents a growing audience of young, active people who take care of their health and use only natural products to look and feel great. Farrah looks fit and fabulous, and takes care of her body, and a lot of health-conscious people can look up to that."