For JWT - the readme contains info: https://github.com/yglukhov/nim-jwt
For 2FA auth, use: https://github.com/OpenSystemsLab/otp.nim
For OAuth, there is this package (see test folder). I haven't used it: https://github.com/CORDEA/oauth
I have a very old blog post that uses standard cookie auth: https://ttj.dk/blog/2019/01/20/setup-a-website-with-nim