Add HE DDNS DNS API

dnsapi2.md

@@ -89,6 +89,7 @@
 - [165. Use Timeweb Cloud DNS API](#dns_timeweb)
 - [166. Use myLoc.de / webtropia.com DNS API](#dns_myloc)
 - [167. Use Yandex 360 for Business DNS API](#dns_yandex360)
+- [168. Use HE DNS DDNS API](#dns_he_ddns)
 - [Use custom API](#dns_myapi)
 - [Use lexicon DNS API](#dns_lexicon)
 
@@ -2266,6 +2267,31 @@ When using OAuth you will need to complete a one-time authorization procedure:
 - [Report any bugs or issues here.](https://github.com/acmesh-official/acme.sh/issues/5213)
 
 
+<a name="dns_he_ddns"/>
+
+## 168. Use HE DDNS DNS API
+
+This uses the Dynamic DNS API in the Hurricane Electric DNS service (https://dns.he.net/).
+
+1. Add new TXT record for `_acme-challenge.example.com` in HE DNS interface, select "Enable entry for dynamic dns"
+(the content will automatically be like "Acme challenge key", that's fine)
+2. Click the "Generate a DDNS key" button in the DDNS column, click the "Generate a key" button in the form,
+copy the key and Submit the form
+3. Set the HE_DDNS_KEY variable:
+```
+export HE_DDNS_KEY="the_generated_key"
+```
+
+To issue a certificate run:
+```sh
+./acme.sh --issue --dns dns_he_ddns -d example.com
+```
+
+The `HE_DDNS_KEY` will be saved in `~/.acme.sh/account.conf` and will be reused when needed.
+
+Report any bugs or issues [here](https://github.com/acmesh-official/acme.sh/issues/5238)
+
+
 <a name="dns_myapi"/>
 
 ## Use custom API