I vibecoded NostrAuth library for dotnet backends so you can just add ".AddNostr()" and your web app has functioning Nostr login. It is small and has no dependencies other than NBitcoin. You can steal it at

GitHub

GitHub - urza/nostr-login: Login to dotnet web app with nostr identity

Login to dotnet web app with nostr identity. Contribute to urza/nostr-login development by creating an account on GitHub.

and test it - come sign my guest book: https://urza.cc