@matty @graf I built the registration microservice on Truth Social, and it involves configurable "challenges" including email verification and SMS verification. Captcha could be a challenge. "I am not a robot" could be a challenge. Etc. Admins can enable and order the challenges however they want.

But for a Fediverse server, IP rate limiting is good enough. "By approval" mode is also a good default unless you have a reason not to be, such as wanting to be a public square. To those who say "then you'll get a flood of approval requests": first of all, enable rate limiting. Second, this is significantly less damage, as it is only an inconvenience to you as an admin rather than an inconvenience to your users and potentially the whole network.