added hcaptcha doc

docs/configuring-captcha.md

@@ -2,9 +2,11 @@
 
 # Overview
 Captcha can be enabled for this home server. This file explains how to do that.
-The captcha mechanism used is Google's [ReCaptcha](https://www.google.com/recaptcha/). This requires API keys from Google.
+The captcha mechanism used is Google's [ReCaptcha](https://www.google.com/recaptcha/). This requires API keys from Google. If your homeserver is Dendrite then [hCapcha](https://www.hcaptcha.com) can be used instead.
 
-## Getting keys
+## ReCaptcha
+
+### Getting keys
 
 Requires a site/secret key pair from:
 
@@ -12,12 +14,39 @@ Requires a site/secret key pair from:
 
 Must be a reCAPTCHA **v2** key using the "I'm not a robot" Checkbox option
 
-## Setting ReCaptcha Keys
+### Setting ReCaptcha keys
 
 Once registered as above, set the following values:
 
 ```yaml
+# for Synapse
 matrix_synapse_enable_registration_captcha: true
 matrix_synapse_recaptcha_public_key: 'YOUR_SITE_KEY'
 matrix_synapse_recaptcha_private_key: 'YOUR_SECRET_KEY'
+
+# for Dendrite
+matrix_dendrite_enable_registration_captcha: true
+matrix_dendrite_recaptcha_public_key: 'YOUR_SITE_KEY'
+matrix_dendrite_recaptcha_private_key: 'YOUR_SECRET_KEY'
+```
+
+## hCaptcha
+
+### Getting keys
+
+Requires a site/secret key pair from:
+
+<https://dashboard.hcaptcha.com/welcome>
+
+### Setting hCaptcha keys
+
+```yaml
+matrix_dendrite_enable_registration_captcha: true
+matrix_dendrite_recaptcha_public_key: 'YOUR_SITE_KEY'
+matrix_dendrite_recaptcha_private_key: 'YOUR_SECRET_KEY'
+
+matrix_dendrite_recaptcha_siteverify_api: 'https://hcaptcha.com/siteverify'
+matrix_dendrite_recaptcha_api_js_url: 'https://js.hcaptcha.com/1/api.js'
+matrix_dendrite_recaptcha_form_field: 'h-captcha-response'
+matrix_dendrite_recaptcha_sitekey_class: 'h-captcha'
 ```