📄️ Let's Encrypt
Let's Encrypt: free and automated SSL/TLS certificates, ACME protocol, domain validation, automatic renewal, HTTPS security, open and trusted certificate authority.
📄️ HTTP-01 Challenge
Let's Encrypt HTTP-01 Challenge: domain validation via token on port 80, most common method to obtain free SSL/TLS certificates with Certbot, Nginx and Apache.
📄️ DNS-01 Challenge
Let's Encrypt DNS-01 Challenge: validation via TXT record in DNS, wildcard certificates, internal servers, automation with DNS provider APIs.
📄️ TLS-ALPN-01 Challenge
Let's Encrypt TLS-ALPN-01 Challenge: validation via TLS handshake on port 443, alternative when port 80 is blocked.
📄️ Advanced Topics
Let's Encrypt advanced topics: troubleshooting common errors, certificate revocation, backup and migration, Certificate Transparency and monitoring.