The acme-challenge is a critical part of the Automated Certificate Management Environment (ACME) protocol, used for the automated issuance of domain-validated TLS certificates. Here's detailed information about this concept:
Overview
The acme-challenge involves proving ownership of a domain name to a Certificate Authority (CA) like Let's Encrypt. This proof is necessary before the CA will issue a certificate for that domain.
Historical Context
How it Works
The acme-challenge process typically includes the following steps:
- Request for Certificate: The domain owner requests a certificate from a CA.
- Challenge Issuance: The CA issues a challenge, which includes a unique token.
- Challenge Response: The domain owner must respond to the challenge by placing the token in a specific location on their web server, usually in the
/.well-known/acme-challenge/ directory.
- Verification: The CA verifies the token by attempting to retrieve it from the domain. If successful, the challenge is considered passed.
- Certificate Issuance: Upon verification, the CA issues the certificate.
Types of Challenges
There are several types of challenges, but the most common are:
- HTTP-01: Involves placing a file with the token in a web server directory.
- DNS-01: Requires creating a TXT record in the domain's DNS zone.
- TLS-ALPN-01: A newer challenge type that uses the TLS Application-Layer Protocol Negotiation extension.
Security Considerations
- The challenge response must be accessible over the internet to allow the CA to verify the ownership.
- The process must be secure to prevent DNS spoofing or other attacks that could compromise the challenge.
Current Use
Today, the acme-challenge is widely used by various services and tools like:
References
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