Add support for Knot DNS API

The script is actually an adapted version of the `dns_nsupdate.sh` script,
as the `knsupdate` utility is quite similar to `nsupdate`.

README.md

@@ -295,6 +295,7 @@ You don't have to do anything manually!
 1. cyon.ch
 1. Domain-Offensive/Resellerinterface/Domainrobot API
 1. Gandi LiveDNS API
+1. Knot DNS API
 
 **More APIs coming soon...**
 

dnsapi/README.md

@@ -349,6 +349,51 @@ Ok, let's issue a cert now:
 acme.sh --issue --dns dns_gandi_livedns -d example.com -d www.example.com
 ```
 
+## 19. Use Knot (knsupdate) DNS API to automatically issue cert
+
+First, generate a TSIG key for updating the zone.
+
+```
+keymgr tsig generate acme_key algorithm hmac-sha512 > /etc/knot/acme.key
+```
+
+Include this key in your knot configuration file.
+
+```
+include: /etc/knot/acme.key
+```
+
+Next, configure your zone to allow dynamic updates.
+
+Dynamic updates for the zone are allowed via proper ACL rule with the `update` action. For in-depth instructions, please see [Knot DNS's documentation](https://www.knot-dns.cz/documentation/).
+
+```
+acl:
+  - id: acme_acl
+    address: 192.168.1.0/24
+    key: acme_key
+    action: update
+
+zone:
+  - domain: example.com
+    file: example.com.zone
+    acl: acme_acl
+```
+
+Finally, make the DNS server and TSIG Key available to `acme.sh`
+
+```
+export KNOT_SERVER="dns.example.com"
+export KNOT_KEY=`grep \# /etc/knot/acme.key | cut -d' ' -f2`
+```
+
+Ok, let's issue a cert now:
+```
+acme.sh --issue --dns dns_knot -d example.com -d www.example.com
+```
+
+The `KNOT_SERVER` and `KNOT_KEY` settings will be saved in `~/.acme.sh/account.conf` and will be reused when needed.
+
 # Use custom API
 
 If your API is not supported yet, you can write your own DNS API.

dnsapi/dns_knot.sh

@@ -0,0 +1,95 @@
+#!/usr/bin/env sh
+
+########  Public functions #####################
+
+#Usage: dns_knot_add   _acme-challenge.www.domain.com   "XKrxpRBosdIKFzxW_CT3KLZNf6q0HG9i01zxXp5CPBs"
+dns_knot_add() {
+  fulldomain=$1
+  txtvalue=$2
+  _checkKey || return 1
+  [ -n "${KNOT_SERVER}" ] || KNOT_SERVER="localhost"
+  # save the dns server and key to the account.conf file.
+  _saveaccountconf KNOT_SERVER "${KNOT_SERVER}"
+  _saveaccountconf KNOT_KEY "${KNOT_KEY}"
+
+  if ! _get_root "$fulldomain"; then
+    _err "Domain does not exist."
+    return 1
+  fi
+
+  _info "Adding ${fulldomain}. 60 TXT \"${txtvalue}\""
+
+  knsupdate -y "${KNOT_KEY}" <<EOF
+server ${KNOT_SERVER}
+zone ${_domain}.
+update add ${fulldomain}. 60 TXT "${txtvalue}"
+send
+quit
+EOF
+
+  if [ $? -ne 0 ]; then
+    _err "Error updating domain."
+    return 1
+  fi
+
+  _info "Domain TXT record successfully added."
+  return 0
+}
+
+#Usage: dns_knot_rm   _acme-challenge.www.domain.com
+dns_knot_rm() {
+  fulldomain=$1
+  _checkKey || return 1
+  [ -n "${KNOT_SERVER}" ] || KNOT_SERVER="localhost"
+
+  if ! _get_root "$fulldomain"; then
+    _err "Domain does not exist."
+    return 1
+  fi
+
+  _info "Removing ${fulldomain}. TXT"
+
+  knsupdate -y "${KNOT_KEY}" <<EOF
+server ${KNOT_SERVER}
+zone ${_domain}.
+update del ${fulldomain}. TXT
+send
+quit
+EOF
+
+  if [ $? -ne 0 ]; then
+    _err "error updating domain"
+    return 1
+  fi
+
+  _info "Domain TXT record successfully deleted."
+  return 0
+}
+
+####################  Private functions below ##################################
+# _acme-challenge.www.domain.com
+# returns
+# _domain=domain.com
+_get_root() {
+  domain=$1
+  i="$(echo "$fulldomain" | tr '.' ' ' | wc -w)"
+  i=$(_math $i - 1)
+
+  while true; do
+    h=$(printf "%s" "$domain" | cut -d . -f $i-100)
+    if [ -z "$h" ]; then
+      return 1
+    fi
+    _domain="$h"
+    return 0
+  done
+  _debug "$domain not found"
+  return 1
+}
+
+_checkKey() {
+  if [ -z "${KNOT_KEY}" ]; then
+    _err "You must specify a TSIG key to authenticate the request."
+    return 1
+  fi
+}