This is an ACME client for ESP (ESP32, etc) devices, so your IoT can fetch their own certificate for secure communication. ACME is a protocol (see <a href="https://tools.ietf.org/html/rfc8555">RFC8555</a>) for automatic certificate management. Sites such as letsencrypt.org allow you to obtain free (no charge) certificates in an automated way using the ACME protocol. Now also supporting the ARI protocol, to learn about when to renew a certificate. Also works with Google ACME, next to Letsencrypt.