Ads.txt is a simple, flexible, and secure method for publishers and distributors to declare who is authorized to sell their inventory, improving transparency for programmatic buyers.
Ads.txt supports transparent programmatic digital media transactions and can remove the financial incentive from selling counterfeit and misrepresented media. Similar to robots.txt, ads.txt can only be posted to a domain by a publisher’s webmaster, making it valid and authentic.
As a text file, ads.txt is easy to update, making it flexible. The data required to populate the file is readily available in the OpenRTB protocol, making it simple to gather and target. And because publishers sell their inventory through a variety of sales channels, ads.txt supports the following types of supplier relationships:
– Domain owners who sell on exchanges through their own accounts
– Networks and sales houses who programmatically sell on behalf of domain owners
– Content syndication partnerships where multiple authorized sellers represent the same inventory

Additional information on Ads.txt is available in the following link leading to IAB’s ads.txt page:

About ads.txt