SuperTokens is an open source authentication solution offering features like: Different types of login: Email / password, Passwordless (OTP or Magic link based).

SuperTokens.com

Is there an easy way to implement guest accounts? Ie generate a token without signup and then convert to a signed up user later?

I would recommend that you make a JWT based session (using Session.createJWT function) that we have.

Then on sign in, you can get the JWT's payload and merge that with the session's access token payload.