.well-known/.well-known/HTTP-01-Challenge
The HTTP-01 Challenge is a method used in the Automated Certificate Management Environment (ACME) protocol to verify domain ownership during the process of issuing a TLS certificate. Here are the detailed aspects:
- Context: The .well-known directory is a standardized path on web servers where specific resources can be found. This directory is used for various protocols to discover information or services related to the domain.
- Function: In the context of ACME, the .well-known/.well-known/HTTP-01-Challenge directory is utilized by Certificate Authorities (CAs) like Let's Encrypt to confirm that the requester of a certificate has control over the domain. Here's how it works:
- A challenge-response is initiated by the CA, where a unique token and a thumbprint of the account key are provided.
- The token is placed in a file under the .well-known/acme-challenge/ directory on the web server.
- The CA attempts to retrieve this file via HTTP to verify that the token matches what was sent.
- History:
- The concept of using a well-known URI for discovery purposes was formalized in RFC 8615.
- The specific use for the HTTP-01 Challenge was introduced with the ACME protocol, which was standardized in RFC 8555.
- Security Considerations:
- The challenge ensures that only those with actual control over the server can issue certificates, reducing the risk of unauthorized certificates being issued.
- However, there are known risks like DNS cache poisoning or server misconfiguration that could compromise the verification process.
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