(Adapted from the upstream project)
Captcha can be enabled for this home server. This file explains how to do that. The captcha mechanism used is Google's ReCaptcha. This requires API keys from Google. If your homeserver is Dendrite then hCapcha can be used instead.
Requires a site/secret key pair from:
http://www.google.com/recaptcha/admin
Must be a reCAPTCHA v2 key using the "I'm not a robot" Checkbox option
Once registered as above, set the following values:
# 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_client_api_enable_registration_captcha: true
matrix_dendrite_client_api_recaptcha_public_key: 'YOUR_SITE_KEY'
matrix_dendrite_client_api_recaptcha_private_key: 'YOUR_SECRET_KEY'
Requires a site/secret key pair from:
https://dashboard.hcaptcha.com/sites/new
matrix_dendrite_client_api_enable_registration_captcha: true
matrix_dendrite_client_api_recaptcha_public_key: 'YOUR_SITE_KEY'
matrix_dendrite_client_api_recaptcha_private_key: 'YOUR_SECRET_KEY'
matrix_dendrite_client_api_recaptcha_siteverify_api: 'https://hcaptcha.com/siteverify'
matrix_dendrite_client_api_recaptcha_api_js_url: 'https://js.hcaptcha.com/1/api.js'
matrix_dendrite_client_api_recaptcha_form_field: 'h-captcha-response'
matrix_dendrite_client_api_recaptcha_sitekey_class: 'h-captcha'