Username/password authentication strategy

[Alex Schroeder]

I'm hoping to collect pieces of advice that apply to all future
developers on a wiki... I hope you're OK with that?

gemini://transjovian.org/phoebe/page/Design

The first post is a copy of Solderpunk's suggestion on how to do
usernames and passwords.

I'd love it if other people also helped collect these, or comment and
refine them, as we all learn more.