Definition
HTTP-01
This is the most common challenge type today. Let’s Encrypt gives a token to your ACME client, and your ACME client puts a file on your web server at
http://<YOUR_DOMAIN>/.well-known/acme-challenge/<TOKEN>That file contains the token, plus a thumbprint of your account key. Once your ACME client tells Let’s Encrypt that the file is ready, Let’s Encrypt tries retrieving it (potentially multiple times from multiple vantage points). If our validation checks get the right responses from your web server, the validation is considered successful and you can go on to issue your certificate. If the validation checks fail, you’ll have to try again with a new certificate.